Thoracic Imaging Flashcards

Question

Perilymphatic Nodules

Answer 1

Perilymphatic nodules follow the anatomic locations of pulmonary lymphatics, which can be seen in three locations in the lung: 1. subpleural 2. Peribronchovascular 3. Septal (within the interlobular septa separating the hexagonal secondary pulmonary lobules). Sarcoidosis is by far the most common cause of perilymphatic nodules, typically with an upper-lobe distribution. The nodules may become confluent creating the galaxy sign. The differential of perilymphatic nodules includes: Sarcoidosis, pneumoconiosis (silicosis and coal workers pneumoconiosis, are reactions to inorganic dust inhalation, the imaging may look identical to sarcoidosis with perilymphatic nodules, but there is usually a history of exposure (e.g. a sandblaster who develops silicosis)), and Lymphangitic carcinomatosis

Answer 2

Randomely distributed nodules usually occur via hematogenous spread and have an angiocentric distribution. The differential of random nodules includes: Hematogenous metastases, septic emboli (embolic infection has a propensity to cavitate but early emboli may be irregular or solid), pulmonary langerhans's cell histiocystosis (PLCH, a smoking-related lung disease that progresses from airway-associated and random nodules to irregular cysts. PLCH is usually distinguishable from other causes of random nodules due to the presence of cysts and non-angiocentric distribution).

Answer 3

A miliary pattern is innumerable tiny random nodules disseminated hematogenously, suggestive of the appearance of millet seeds. The differential of miliary nodules includes: disseminated tuberculosis, disseminated fungal infection, disseminated hematogenous metastases.

Answer 4

Tree-in-bud nodules are multiple small nodules connected to linear branching structures, which resembles a budding tree branch in springtime as seen on CT. The linear branching structures represent the impacted bronchioles, which are normally invisible on CT, and the nodules represent the impacted terminal bronchioles. Tree-in-bud nodules are due to mucs, pus, or fluid impacting bronchioles and terminal bronchioles. Tree-in-bud nodules are almost always associated with small airways infection, such as endobronchial spread of tuberculosis. The differential of tree-in-bud nodules include: Mycobacteria tuberculosis and aytpical mycobacteria, bacterial pneumonia, aspiration pneumonia, airway-infasive aspergillus (aspergillus is an opportunistic fungus with several patterns of disease. The airway-invasive pattern is seen in immunocompromised patients and may represent either as bronchopneumonia or small airways infection)

Answer 5

A cavitary lesion has a thick, irregular wall, often with a solid mural component. Although the findings of benign and malignant cavitary nodules overlap, a maximum wall thickness of = 4mm is usually benign and a wall thickness of \>15 mm is usually malignant. Spiculated margins also suggest malignancy. A solitary cavitary lesion is most likely cancer or infection. Primary bronchogenic carcinoma (while both squamous cell and adenocarcinoma can cavitate, squamous cell cavitates more frequently. Small cell carcinoma is never known to cavitate.) Tuberculosis (classically produces an upper-lobe cavitation).

Answer 6

Multiple cavitary lesions are typically vascular or spread through the vascular system: Septic emboli, vasculitis (including Wegener granulomatosis, which is especially prone to cavitate), metastases (of which squamous cell carcinoma and uterine carcinosaroma are known to cavitate).

Answer 7

A cyst is an air-containing lucency with a thin, nearly imperceptible wall. In general, cystic lung disease is usually due to a primary airway abnormality.

Answer 8

Lymphangiomyomatosis (LAM) - a diffuse cystic lung disease caused by smooth muscle proliferation of the distal airways. LAM causes uniformly distributed, thin-walled cysts in a diffuse distribution. It is classically associated with chylous effusion. Emphysema - which tends to be upper lobe predominant in a smoker Pulmonary Langerhans cell histiocytosis - which features irregular cysts and nodules predominantly in the upper lungs. Diffuse cystic bronchiectasis - Bronchiectasis is dilation of the bronchioles. Although cystic fibrosis is the most common cause of bronchiectasis and has an upper-lobe predominance, congenital or post-infectious causes can have a diffuse or lower-lobe distribution. Pneumocystis jiroveci pneumonia - which features cysts in late-stage disease. Lymphoid interstitial pneumonia (LIP) - an exceptionally rare disease usually associated with Sjogren syndrome and characterized by alveolar distortion from lymphocytic infiltrate and multiple cysts.

Answer 9

The differential for a single lung cyst includes: Bulla - an air filled cyst measuring \>1 cm. A giant bulla occupies at least 30% of the volume of the thorax. Bleb - air filled cystic structure contiguous with the pleura measuring \<1 cm. Rupture of a bleb is the most common cause of spontaneous pneumothorax. Pneumatocele - air-filled space caused by prior lung trauma or infection.

Answer 10

The differential diagnosis of basal-predominant fibrotic change includes: Idiopathic pulmonary fibrosis (IPF) - clinical syndrome of progressive pulmonary fibrosis of unknown etiology and is most common cause of basilar fibrosis. It almost always features basilar honeycombing. End-stage asbestosis - Asbestosis is an asbestos-induced inflammatory process ultimately producing pulmonary fibrosis. Usually other signs of asbestos exposure are present, such as pleaural plaques. Nonspecific interstitial pneumonia (NSIP), fibrotic form - NSIP is an idiopathic pneumonia. It is a lung response to injury commonly associated with collagen vascular disease and drug reaction. The two histologic subtypes are cellular and fibrotic forms, of which the latter may produce basal-predominant fibrosis. In contrast to IPF, honeycombing is usually absent.

Answer 11

Although IPF is the most common cuase of pulmonary fibrosis, fibrosis primarily affecting the upper lobes should raise concern for an alternative diagnoses, such as: End-stage sarcoidosis (Sarcoidosis is a disease that primarily affects the upper lobes. The late stage of sarcoidosis leads to upper-lobe predominant fibrosis), Chronic hypersensitivity pneumonitis (may cause upper-lobe fibrosis in long-standing disease), end-stage silicosis (the late stage of silicosis may lead to fibrosis with an upper lobe predominance)

Answer 12

S. pneumoniae is the most common cause of CAP. Atypical pneumonia, including Mycoplasma, viral, and Chlamydia, typically infects young and otherwise healthy patients (Mycoplasma has a varied appearance and can produce consolidation, areas of ground glass attenuation, centrilobular nodules, and tree-in-bud nodules). Legionella most commonly occurs in elderly smokers. Infections tend to be severe. (Peripheral consolidation often progresses to lobar and multifocal pneumonia) Infection by Klebsiella and other gram-negatives occurs in alcoholics and aspirators. (Klebsiella classically leads to voluminous inflammatory exudates causing the bulging fissure sign)

Answer 13

HAP occurs in hospitalized patients and is due to aspiration of colonized secretions. HAP is caused by a wide variety of organisms, but the most important pathogens include MRSA and resistant gram-negatives including Pseudomonas.

Answer 14

HCAP defined as pneumonia in a nursing home resident or in a patient with a \>2 day hospitalization over the past 90 days. Pathogens are similar to HAP.

Answer 15

Ventilator associated pneumonia is caused by infectious agents not present at the time mechanical ventilation was started. Most infections are polymicrobial and primarily involve gram-negative rods such as Pseudomonas and Actinetobacter.

Answer 16

Any of the above pathogens, plus opportunistic infections including Pneumocystis, fungi such as Aspergillus, Nocardia, CMV etc., can be seen in immunocompromised patients.

Answer 17

Lobar pneumonia is consolidation of a single lobe. It is usually bacterial in origin and is the most common presentation of community acquried pneumonia. The larger bronchi remain patent, causing air bronchograms.

Answer 18

Lobular pneumonia manifests as patchy consolidation with poorly defined airspace opacities, usually involving several lobes, and most commonly due to S. aureus.

Answer 19

Interstitial pneumonia is caused by inflammatory cells located predominately in the interstitial tissue of the alveolar septa causing diffuse or patchy ground glass opacification. It can be caused by viral pneumonia, Mycoplasma, Chlamydia, or Pneumocystis.

Answer 20

Round pneumonia is an infectious mass-like opacity seen only in children, most commonly due to Streptococcus pneumoniae. Infection remains somewhat confined due to incomplete formation of pores of Kohn.

Answer 21

Necrosis of the lung parenchyma typically due to Stayphylococcus aureas, pseudomonas, or anaerobic bacteria. An air-fluid level is almost always present. An abscess is usually sphericl, with equal dimensions on frontal and lateral views.

Answer 22

Pulmonary gangrene is a very rare complication of pneumonia where there is extensive necrosis or sloughing of a pulmonary segment of lobe. Pulmonary gangrene is a severe manifestation of pulmonary abscess.

Answer 23

Empyema is infection within the pleural space. There are three stages in the development of an empyema: 1. Free-flowing exudative effusion (can be treated with needle aspiration or simple drain) 2. Development of fibrous strands (requires large-bore chest tube and fibrinolytic therapy) 3. Fluid becomes solid and jelly-like (usually requries surgery). Although pneumonia is often associated with a parapneumonic effusion, most pleural effusions associateed with pneumonia are not empyema, but are instead a sterile effusion caused by increased capillary permeability. An empyema confomrs to the shape fo the pleural space, causing a longer air-filled level on the lateral radiograph. This is in contrast to an abscess, discussed above, which typically is spherical and has the same dimensions on the frontal and lateral radiographs. The split pleura sign describes enchancing parietal and visceral pleura of an empyema seen on contrast-enhanced study.

Answer 24

Thin-walled gas-filled cyst that may be post-traumatic or develop as a sequela of pneumonia, typically from Staphylococcus aureus or Pneumocystis. Pneumatoceles almost always resolve.

Answer 25

Bronchopleural fistula is an abnormal communication between the airway and the pleural space. It is caused by rupture of the visceral pleura. By far the most common cause of BPF is surgery; however, other etiologies include lung abscess, empyema, and trauma. On imaging, new or increasing gas is present in a pleural effusion. A connection between the bronchial tree and the pleura is not always apparent, but is helpful when seen. The treatment of BPF is controversial and highly individualized.

Answer 26

Extension of an empyema to the chest wall, most commonly secondary to tuberculosis. Other causative organisms include Nocardia and Actinomyces.

Answer 27

Tuberculosis cause by Mycobacterium tuberculosis, remains an important disease despite remarkable progress in public health and antituberculous therapy over the past century. Tuberculosis remains a significant problem in developing countries. In the United States, TB is seen primarily in the immigrant population and immunocompromised individuals. Initial exposure to TB can lead to two clinical outcomes: 1. Contained disease (90%) results in calcified granulomas and/or calcified hilar lymph nodes. In a patient with normal immunity, the tuberculous bacilli are sequestered with a caseating granulomatous response. 2. Primary tuberculosis results when the host cannot contain the organism. Primary tuberculosis is seen more commonly in children and immunocompromised patients. Reactivation (post-primary) TB is reactivation of a previously latent infection.

Answer 28

Primary tuberculosis represents infection from the first exposure to TB. Primary TB may inovle the pulmonary parenchyma, the airways, and the pleura. Primary TB often causes adenopathy. As many as 15% of patients infected with primary TB have no radiographic changes and the imaging appearance of primary tuberculosis is nonspecific. The four imaging manifestations of primary TB (of which any, non, or all may be present) are ill-defined consolidation, pleural effusion, lymphadenopathy, and miliary disease. Primary TB may occur in any lobe, but the most typical locations are the lower lobes or right middle lobe. It can be difficult to distinguish between primary and post-primary TB, and in clinical practice, the treatment (antituberculous therapy) is the same. Classic imaging findings are not always seen but include: Ghon focus (initial focus of parenchyal infection, usually located in the upper part of the lower lobe or the upper lobe. Ranke complex (Ghon focus and lymphadenopathy). Cavitation is rare in primary TB, in contrast to reactivation TB. Adenopathy is common in primary TB, typically featuring central low-attenuation and peripheral enhancement, especially in children. In contrast, post-primary TB does not feature prominent adenopathy.

Answer 29

Reactivation TB, also called post-primary TB, usually occurs in adolescents and adults and is caused by reactivation of a dormant infection acquried earlier in life. Clinical manifestations of reactivation TB include chronic cough, low-grade fever, hemoptysis, and night sweats. Reactivation TB most common occurs in the upper lobe apical and posterior segments. In an immunocompetent patient, the imaging hallmarks of reactivation TB are upper-lobe predominant disease with cavitation and lack of adenopathy. Focal upper lobe consolidation and endobronchial spread are common. Although not specific to TB, tree-in-bud nodules suggest active endobronchial spread. In an immunosuppressed patient (such as HIV), low-attenuation adenopathy is a typical additional finding, similar to the adenopathy seen in primary TB. Low density lymph nodes may mimic immune reconstitution syndrome in HIV patients. A tuberculoma is a well-defined rounded opacity usually in the upper lobes.

Answer 30

Healed TB is evident on radiolgraphy as apical scarring, usually with upper lobe volume loss and superior hilar retraction. Calcified granulomas may be present as well, which indicate containment of the initial infection by a delayed hypersensitivity response.

Answer 31

Miliary tuberculosis is a diffuse random distribution of tiny nodules seen in hematogenously disseminated TB. Miliary TB can occur in primary or reactivation TB.

Answer 32

The classic presentation of atypical mycobacteria is an elderly woman with cough, low-grade fever, and weight-loss, called Lady Windermere syndrome. Mycobacterium avium intracellulare and M. kansasii are the two most ommon organisms. Classic radiographic findings are bronchiectasis and tree-in-bud nodules, most common in the right middle lobe or lingula.

Answer 33

"Hot-tub" lung is a hypersensitivity pneumonitis in response to atypical mycobacteria which are often found in hot tubs. There is no active infection and the typical patient is otherwise healthy. Imaging is similar to other causes of hypersensitivity pneumonitis, featuring centrilobular nodules.

Answer 34

Endemic fungi can cause community acquired pneumonia in normal individuals, wieth each subtype having a specific geographic distribution. Most infected patients are asymptomatic.

Answer 35

Histoplasma capsulatum is localized to the Ohio and Mississippi river valleys, in soil contaminated with bat or bird guano. The most common sequela of infection is a calcified granuloma. A less common radiologic manifestation is a pulmonary nodule (histoplasmoma), which can mimic a neoplasm. Chronic infection can mimic reactivation TB with upper lobe fibrocavitary consolidation. Fibrosisng mediastinitis is a rare complication of Histoplasma infection of mediastinal lymph nodes leading to pulmonary venous obstruction, bronchial stenosis, and pulmonary artery stenosis. Affected lymph nodes tend to calcify.

Answer 36

Coccidioides immitis is found in the southwestern US and has a variety of radiologic appearances, including multifocal consolidation, multiple pulmonary nodules, and miliary nodules. Blastomyces dermatitidis is found in central and southeastern US. Infection is usually asymptomatic, but may present as flu-like illness that can progress to multifocal consolidation, ARDS, or miliary disease.

Answer 37

Immunosuppressed patients are susceptible to the same organisms that infect immunocompetent patients; however, one must be aware of several additional opportunistic organisms that may present in the immunocompromised. An immunocompromised patient with a focal air space opacity is most likely to have a bacterial pneumonia (most commonly pneumococcus), but TB should also be considered if the CD4 count is low. In contrast, multifocal opacities have a wider differential diagnosis including Pneumocystis pneumonia and opportunistic fungal infection such as Cryptococcus or Aspergillus.

Answer 38

Pneumocystsis jiroveci (previously called Pneumocystis carinii) is an opportunistic fungus that may cause pneumonia in individuals with CD4 counts \<200 cells/cc. The incidence of Pneumocystis pneumonia is decreasing due to routine antibiotic prophylaxis. Chest radiograph findings can be normal but a classic finding of Pneumocystis pneumonia is bilateral perihilar (central) airspace opacities with peripheral sparing. The classic CT appearance is geometric perihilar ground glass opacification, sometimes with crazy paving (ground glass and thickening of the interlobular septa). A normal CT rules out Pneumocystis pneumonia; however, the disease can hide in a normal chest radiograph. Pneumocystis pneumonia has a propensity to cause upper lobe pneumatoceles, which may predispose to pneumothorax or pneumomediastinum.

Answer 39

Cryptococcus is an opportunisitc organism and ist he most common fungal infection in AIDS patients. Pulmonary infection usually coexists with cryptococcal meningitis (Typically CD4 count is less than 100 cells/cc in affected individuals) In the immunosuppressed, Cryptococcus can have a wide range of appearances ranging from ground glass attenuation to focal consolidation to cavitating nodules. Cryptococcus can also prsent as miliary disease, often associated with lymphadenopathy or effusions.

Answer 40

Aspergillus is an ubiquitous soil fungus that manifests as five distinct categories of pulmonary disease. Aspergillus only affects individuals with abnormal immunity or preexisting pulmonary disease. Depending on the manifestation, the predisposing abnormality may include asthma, immunocompromised state, prior infection, or structural/congenital abnormality.

Answer 41

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to aspergillus seen most commonly in patients with long-standing asthma. Patients present clinically with recurrent wheezing, low-grade fever, cough, and sputum production. The sputum contains fragments of aspergillus hyphae. The key finding on CT is upper lobe bronchiectasis and mucoid impaction, which can be high attenuation or even calcified. This combination of mucoid impaction within the bronchiectatic airways represents the finger-in-glove sign (The finger-in-glove sign is not specific to ABPA and can also be seen in segmental bronchial atresia and many other diseases including cystic fibrosis (less commonly seen on a case-by-case basis).

Answer 42

An aspergilloma is a conglomeration of intertwined aspergillus fungal hyphae and cellular debris (a mycetoma or "fungus ball") in a preexisting pulmonary cavity (The aspergilloma is mobile and will change position when the patient is imaged in a different position) The most common causes of a preexisting cavity are prior tuberculosis and sarcoidosis (less common causes include congenital anomalies such as bronchogenic cyst or sequestration, and post-infectious/post-traumatic pneumatocele) If an aspergilloma is symptomatic, hemoptyssi is the most common symptom. When a crescent of air is seen outlining the mycetoma against the wall of the cavity, the correct term is Monod sign. The air crescent sign is reserved for angioinvasive aspergillus.

Answer 43

Semi-invasive aspergillosis is a necrotizing granulomatous inflammation (analogous in pathology to reactivation TB) in response to chronic aspergillus infection. Semi-invasive aspergillosis is seen in debilitated, diabetic, alcoholic, and COPD patients. Clinical symptoms include cough, chronic fever, and less commonly hemoptysis. On CT, there are segmental areas of consolidation, often with cavitation and pleural thickening, which progress slowly over months or years.

Answer 44

Airway-invasive aspergillosis is aspergillus infection deep to the airway epithelial cells. It is seen only in the immunocompromised, including neutropenic and AIDS patients. The spectrum of clinical disease ranges from bronchilitis to bronchopneumonia. The main CT findings of airway-invasive aspergillosis are centrilobular and tree-in-bud nodules. When bronchopneumonia is present, radiograph and CT findings are indistinguishable from other causes of bronchopneumonia, such as Staph aureus.

Answer 45

Angioinvasive aspergillosis is an aggressive infection characterized by invasion and occlusion of arteriorles and smaller pulmonary arteries by fungal hyphae. Angioinvasive aspergillosis is seen almost exclusively in the severely immunocompromised, including patients on chemotherapy, stem cell or solid organ transplant recipients, and in AIDS. The CT halo sign represents a halo of ground glass attenuation surrounding a consolidation. The ground glas is thought to correspond to hemorrhagic infarction of the lung.

Answer 46

Can be seen in viral infection, Wegener granulomatosis, Kaposi sarcoma, hemorrhagic metastasis, angioinvasive aspergillus, and others.

Answer 47

Visually similar to Monod sign surrounding a mycetoma, represents a crescent of air from retraction of infarcted lung. It is a good prognostic sign as it indicates taht the patient is in the recovery phase.

Answer 48

The radiographic severity of pulmonary edema typically progresses through three stages, corresponding to progressively increased pulmonary venous pressures Vascular redistrubution is the first radiographic sign of increased pulmonary venous pressure. Imaging shows increased caliber of the upper lobe vessels compared to the lower lobe vessels. Interstitial edema is caused by increased fluid within the pulmonary veins, which surround the periphery of each hexagonal secondary pulmonary lobule. On radiography, there are incrased intertitial markings, indistinctness of the pulmonary vasculature, peribronchial cuffing, and Kerley B and A lines (Kerley B lines are seen at the peripheral lung and represent thickened interlobular septa, Kerley A lines radiate outward from the hila and may represent dilation of lymphatic channels. They are not thought to be clinically relevant) Alveolar edema is caused by filling of the alveoli with fluid. On imaging, perihilar (central) opacifications are present. Pleural effusions and cardiomegaly are often present. CT findings of pulmonary edema include dependent ground glass opacification and interlobular septal thickening. Intrathoracic causes of pulmonary edema, such as heart failure, generally cause patchy ground glass, while systemic cause of pulmonary edema (e.g., sepsis or low protein states) often cause diffuse ground glass. Pulmonary edema is usually symmetric and dependent. A classic cause of asymmetric pulmonary edema is isolated right upper lobe pulmonary edema, caused by acute mitral regurgitation secondary to myocardial infarction and papillary muscle rupture. A complication of aggressive thoracentesis is reexpansion pulmonary edema, caused by rapid reexpansion of a lung in a state of collapse for more than three days.

Answer 49

The vascular pedicleis the transverse width of the upper mediastinum. (The right border of the vascular pedicle is the interface of the superior vena cava (SVC) and the right mainstem bronchus The vascular pedicle width is normally \<58 mm An interval increase in vascular pedicle width (both \>63 and \>70 mm have been proposed as cutoffs) on sequential supine AP ICU-type chest radiographs generally correlates with increased pulmonary capillary wedge pressure (\>18 mm Hg) and fluid overload

Answer 50

The endotracheal tube tip should be approximately 4-6 cm above the carina with the neck in neutral alignment. However, in situations with low pulmonary compliance (e.g., ARDS), a tip position closer to the carina may reduce barotrauma. Direct intubation of either the right or left mainstem bronchus (right mainstem bronchus far more common) is an emergent finding that can cause complete atelectasis of the un-intubated lung.

Answer 51

The tip of a central venous catheter, including a PICC, should be in the lower SVC or the cavoatrial junction. Azygos malposition is seen in approximately 1% of bedside-placed PICCs. Azygos malposition is associated with increased risk of venous perforation and catheter-associated thrombosis, and repositioning is recommended. A dialysis catheter should be located in the right atrium.

Answer 52

The tip of a Swan-Ganz pulmonary artery catheter should either be in the main, right, or left pulmonary artery. If the tip is distal to the proximal interlobar pulmonary artery, there is a risk of pulmonary artery rupture or pseudoaneurysm. Other complications of pulmonary artery catheter placement include intracardiac catheter knot and arrythmia.

Answer 53

Lung cancer is the leading cause of cancer death in the USA. Including all subtypes, the 5-year survival is 15%. Tobacco smoking is thought to cause 80-90% of lung cancersl (almost all cases of squamous cell and small cell carcinoma are seen in smokers. Adenocarcinoma is also associated with smoking, but primary bronchogenic carcinoma arising in a lifelong nonsmoker with no history of secondhand exposure is almost always adenocarcinoma). Occupational and environmental exposures, including beryllium, radon, arsenic, etc., remain an important risk factor for lung cancer. Asbestos exposure increases the risk of lung cancer by a factor of five, synergistic with smoking. Pulmonary fibrosis increases the risk of lung cancer by a factor of ten. Pulmonary scarring, such as from prior TB, also increases the risk of lung cancer.

Answer 54

Pulmonary nodules are very common and the vast majority are benign; however, nodules are often followed with serial CT scans to screen for development of lung cancer. Calcified nodules are usually benign. Although less commonly seen, ground glass nodules ( or mixed attenuation nodules containing both solid and ground glass) are more likely to be malignant than a solid nodule. Central, laminar, and diffuse calcifications are almost always benign. Popcorn calcification, suggestive of a pulmonary hemartoma, is benign. Intra-lesional fat, suggestive of hamartoma or lipoid granuloma is benign. Small nodules are usually benign. A nodule \<3 mm has a 0.2% chance of being cancer and a 4-7 mm nodule is malignant in 2.7% of cases. Any calcification in a small nodule is usually benign. Non-round shape, including oblong, polygonal, triangular, or geometric is probably benign. Subpleural location is often benign. Clustering of nodules suggests an infectious process. Large size is the single most important risk factor for malignancy, regardless of morphology; 0.8 to 3 cm nodules have 18% risk of being lung cancer and massess \>3 cm have a very high chance of being malignant. Irregular edge or spiculated margin is concerning. Round shape (as opposed to oblong) is suggestive of malignancy. A cavitary nodule or nodule containing small cystic spaces is suspicious for malignancy.

Answer 55

Follow-up is not recommended for a solitary pulmonary nodule if the nodule is small (\<4 mm) and the patient doesn't have a history of smoking or other risk factors. Any interval nodule growth is suspicious. A 26% increase in diameter (for instance, from 1.0 to 1.26 cm) is doubling in volume. (Doubling time for lung cancers ranges from 42 days in very aggressive tumors to over 4 years in indolent lesions such as bronchioalveolar carcinoma.) A nodule that has not changed in size over 2 years is very likely, but no definitely, benign. Follow-up of ground glass nodules, which are often indolent bronchioloalveolar carcinoma, may be appropriate beyond 2 years. A decrease in size of a suspicious nodule on a single follow up study is not sufficient to establish a benign etiology (transient decrease in size of a malignant lesion can occur with collapse of aerated alveoli or necrosis) The Fleischner Society (2005) suggests the following follow-up recommendations for noncalcified nodules in patients older than 35 without a history of malignancy. A high-risk patient is defined as a patient with a history of smoking or other risk factors for lung cancer. (refer to more recent Fleischner guidelines).

Answer 56

Lung cancer can be thought of as two types: "small-cell" and all other histologic types that are not small cell, such as adenocarcinoma, squamous cell carcinoma, etc. However, although previously small cell and non-small cell used separate staging systems, the 2009 staging revision unifies the staging of all types. Small cell is usually disseminated at diagnosis and has a much worse prognosis.

Answer 57

Adenocarcinoma is the most common subtype of lung cancer. It is related to smoking, but less strongly than squamous cell. Adenocarcinoma tends to occur in the peripheral lung. The typical radiographic appearance of adenocarcinoma is of a pulmonary nodule, which often has a spiculated margin due to reactive fibrosis. Cavitation can occur but is less commonly seen compared to squamous cell. A useful pathologic marker is TTF-1 (thyroid transcription factor), which is positive in primary lung adenocarcinoma and negative in pulmonary metastases from an extrathoracic adenocarcinoma.

Answer 58

Squamous cell carcinoma is slightly less common toay than adenocarcinoma. Prior to filtered cigarettes, SCC was more common. The majoirty of SCC arise centrally from main, lobar, or segmental bronchi, where the tumor tends to cause symptoms early due to bronchial obstruction. SCC may also present as a hilar mass. Common radiographic findings are lobar atelectasis, mucoid impaction, consolidation, and bronchiectasis. SCC has a propensity to cavitate.

Answer 59

(BAC) refers to a spectrum of well-differentiated adenocarcinoma that demonstrates lepidic growth. The hallmark of lepidic growth is a spreading of malignant cells using the alveolar walls as a scaffold. (The opposite of lepidic growth is hilic growth, demonstrated by most other forms of lung cancer, which describes cancer growth by invasion and destruction of lung parenchyma) A spectrum of lesions have been called BAC ranging from small peripheral tumors with 100% survival to lesions causing widespread advanced disease. Despite this variability BAC is most commonly indolent and is often negative on PET. To create more uniformity in the pathological, clinical, and research domains, a new classification for the spectrum of the adenocarcinoma subtypes formerly called BAC has recently been proposed. This classification is primarily based on the pathology of the lesion and differentiation of these entities on imaging is difficult. In clinical radiologic practice, this spectrum of lesions is routinely still referred to as BAC. This textbook will continue the common practice and refer to these lesions as BAC. (Adenomatous hyperplasia (AAH): a precursor lesion, Adenocarcinoma in situ: a preinvasive lesion, minimally invasive adenocarcinoma, adenocarcinoma predominantly invasive with some nonmucinous lepidic component: formerly nonmucinous BAC, invasive mucinous adenocarcinoma: formerly mucinous BAC nonmucinous and mucinous subtypes of BAC occur with approximately equal prevalence)

Answer 60

(adenocarcinoma, predominantly invasive with some nonmucinous lepidic component) classically presents as a ground glass or solid nodule with air bronchograms and has a better prognosis compared to the mucinous subtype.

Answer 61

(Invasive mucinous adenocarcinoma) tends to present with chronic consolidation. It has a worse prognosis compared with non-mucinous BAC.

Answer 62

Small cell carcinoma is the third most common lung cancer cell type (after adenocarcinoma and squamous cell). Neoplastic cells are of neuroendocrine origin and are associated with various paraneoplastic syndromes. Small cell carcinoma is strongly associated with smoking. Small cell tends to occur in central bronchi with invasion through the bronchial wall, typically presenting as a large hilar or parahilar mass. Involvment of the SVC may cause SVC syndrome. Small cell rarely presents as a solitary pulmonary nodule. Small cell is considered a disseminated disease and is generally not amenable to surgery.

Answer 63

Large cell carcinoma is a wastebasket patholigic diagnosis for tumors that are not squamous, adenocarcinoma, or small cell. Large cell carcinoma is strongly associated with smoking and has a poor prognosis. Large cell carcinoma often occurs in the lung periphery, wher it presents as a large mass.

Answer 64

Neoplastic carcinoid cells originate from neuroendocrine cells in the bronchial walls. A common presentation of carcinoid is an endobronchial mass distal to the carina, which may cause obstructive atelectasis. Up to 20% of cases present as a pulmonary nodule. Carcinoid may be typical (low-grade) or the more aggressive atypical variant. Typical carcinoids without nodal or distant metastses have an excellent prognosis (92% 5-year survival). Atypical carcinoids tend to arise peripherally and have a worse prognosis. Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is an extremely uncommon precursor lesion to typical carcinoid tumor, characterized by multiple foci of neuroendocrine hyperplasia or tumorlets (carcinoid foci \<5 mm in size) and bronchiolitis obliterans.

Answer 65

A nodule is defined as \<3 cm and a mass is \>3 cm. Adenocarcinoma, including subtypes formerly called BAC, comprises approximately 50% of cancers presenting as a solitary pulmonary nodule.

Answer 66

Atelectasis due to bronchial obstruction is a common presentation of lung cancer. Despite the presence of atelectasis, volume loss is variable, secondary to the volume-displacing effects of desquamated cells, mucus, and fluid. Obstructive pneumonia is a common presentation of lung cancer, caused by bronchial obstruction and parenchymal consolidation by inflammatory cells and lipid-laden macrophages. If two foci of atelectasis are present simultaneously that cannot be explained by a single endobronchial lesion, a benign process is much more likely. However, CT and bronchoscopy are still needed for workup.

Answer 67

Consolidation that is indistinguishable from pneumonia can be seen with BAC (mucinous subtype). Although BAC and pneumonia may appear similar, BAC is usually a non-resolving consolidation with (near) normal white blood cell count.

Answer 68

A hilar mass is a common presentation of squamous cell and small cell carcinoa. Hilar enlargement may be due to a primary central tumor or nodal metastasis from a parenchymal neoplasm. Tumor may compress and narrow the bronchus. A tapered bronchus is highly specific for lung cancer.

Answer 69

A superior sulcus tuor is a lung cancer occurring in the lung apex. A Pancoast tumor is a type of superior sulcus tumor with involvement of the sympathetic ganglia causing a Horner syndrome, with ipsilateral ptosis, miosis, and anhidrosis. A superior sulcus tumor is a stage T3 tumor.

Answer 70

Lymphangitic carcinomatosis represents diffuse spread of neoplasm through the pulmonary lymphatics, typically seen in late-stage disease. On imaging, carcinomatosis manifests as nodular interlobular septal thickening, which is usually asymmetric.

Answer 71

Pleural effusions are relatively common in lung cancer, and may be due to lymphatic obstruction or pleural metastases. A malignant effusion is the presence of malignant cells within the effusion. A malignant effusion is an M1a lesion, which precludes curative resection. Not all effusions associated with lung cancer are malignant effusions, so cytologic evaluation is necessary.

Answer 72

Pneumothorax is not a common presentation of lung cancer, but can be seen with peripheral tumors that cavitate or invade into the pleura.

Answer 73

The 7th edition fo the TNM system, published 2009, is based on data collected on over 100,000 patients with lung cancer from 1990 to 2000. Staging of small cell lung cancer was previously simplified to "limited-stage" or "extensive-stage". The new 7th TNM system, however, recommends that the same TNM staging system be used for both small cell and non-small cell lung cancer.

Answer 74

For early stagesup to IIB and sometimes IIIA, surgery is usually performed. Neoadjuvant or adjuvant chemotherapy and radiotherapy can be used. Stage IIIB (N3 - contralateral or supraclavicular nodes; or T4/N2) is unresectable. Stage IV disease is generally not treated surgically unless there is a solitary adrenal or brain metastasis.

Answer 75

T1: Tumor = 3 cm surrounded by lung or visceral pleura. (T1a: Tumor = 2 cm; 5-year survival rate 77%; T1b: \>2 cm and = 3 cm; 5 year survival rate 71%) T2: Tumor \>3 cm and =7 cm, or local invasion of the visceral pleura, or endobronchial lesions \>2 cm from the carina. (T2a: \>3 cm and = 5 cm; 5-year survival rate 58%; T2b: \>5 and =7 cm; 5-year survival rate 49%) T3: Tumor \>7 cm, or local invasion of chest wall, diaphragm, pleura, or superior sulcus tumor, or endobronchial lesion \<2 cm from carina. (T3: 5-year survival rate 35% T3: Separate tumor nodule in the same lobe; 5-year survival rate 28%) T4: Separate tumor nodule in a different lobe in the ipsilateral lung, or tumor of any size with invasion of mediastinal structures included carina, heart, great vessels, or vertebral bodies (T4: 5-year survival rate 22%)

Answer 76

The color coding of the lymph nodes on the diagram below represents the nodal staging of lung cancer for an example of a left-sided mass: N0: No lymph node metastases. N1: Ipsilateral hilar or intrapulmonary lymph nodes. N2: Ipsilateral mediastinal nodes. N3: Contralateral lymph nodes or supraclavicular nodes on either side.

Answer 77

M0: No metastatic disease. M1a: Local thoracic metastatic disease (Separate tumor nodule in contralateral lung; 5-year survival rate 3%. Malignant pleural or pericardial effusion; 5-year survival rate 2%) M1b: Distant or extrathoracic metastatic disease (Median survival 6 months. 1-year survival rate 22%)

Answer 78

Clinically, the term pulmonary hypertension is used to encompass both pulmonary arterial and pulmonary venous hypertension. The term pulmonary arterial hypertension (PAH) is generally reserved for the WHO class 1 entities. It may be clinically difficult to distinguish pulmonary arterial from pulmonary venous hypertension. Furthery complicating the distinction, venous hypertension may be a cause of arterial hypertension. Pulmonary arterial hypertension is defined as pulmonary arterial systolic pressure \>/= 25 mm Hg at rest or \>/= 30 mm Hg during exercise. Elevated pulmonary venous pressures are present when pulmonary capillary wedge pressure (an approximation of pulmonary venous pressure) is \>/=18 mm Hg.

Answer 79

There are a number of causes of pulmonary hypertension including chronic thromboembolic disease, chronic respiratory disease, chronic heart disease, and idiopathic causes. The classification in widest usein the radiology literature is the hemodynamic division of precapillary and postcapillary etiologies (In precapillary causes of pulmonary hypertension, the primary abnormailty is either the pulmonary arterial system or pulmonary arterial blood flow. Abnormalities of the pulmonary parenchyma leading to chronic alveolar hypoxia are also included in this category. In postcapillary causes of pulmonary hypertension, an abnormality of the pulmonary veins or elevation of pulmonary venous pressure leads to pulmonary arterial hypertension.) In contrast, the World Health Organization (WHO) clinical classification, based on the 2003 World Symposium on Pulmonary Hypertension, describes five groups of pulmonary hypertension based on etiology. There is no correlation between the pre/postcapillary classification and the WHO classification, and in fact there can be both pre- and postcapillary etiologies within a single WHO group. Group 1: Pulmonary arterial hypertension (PAH). (Primary pulmonary hypertension (PPH) may be idiopathic or familial. Congenital left-to-right shunts, such as atrial septal defect (ASD) and ventricular septal defect (VSD), may cause PAH and shunt reversal (Eisenmenger syndrome). PAH may be caused by pulmonary venous or capillary involvement, wuch as pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis. Group 2: Pulmonary venous hypertension (Left-sided heart disease (left atrial, left ventricular, or mitral/aortic valve disease) may cause elevated pulmonary venous pressure in chronic disease) Group 3: Pulmonary hypertension associated with chronic hypoxemia. (COPD, interstitial lung disease, and sleep apnea can cause pulmonary hypertension in chronic disease) Group 4: Pulmonary hypertension due to chronic thromboembolic disease. Group 5: Pulmonary hypertension due to miscellaneous disorders. (Sarcoidosis is a rare cause of pulmonary hypertension, Compression of pulmonary vessels, which can be due to neoplasm, fibrosing mediastinitis, etc., may cause pulmonary hypertension)

Answer 80

A main pulmonary artery diameter \>/= 2.9 cm suggests the presence of pulmonary hypertension, although pulmonary hypertension may be present in a normal caliber pulmonary artery. A main pulmonary artery diameter larger than the aortic root diameter is also suggestive of pulmonary hypertension. Pulmonary artery calcifications are pathognomonic for chronic pulmonary artery hypertension. Pulmonary hypertension may cause mosaic attenuation due to perfusion abnormalities, most commonly seen in chronic thromboembolic pulmonary hypertension (CTEPH) Pulmonary hypertension may be associated with ground glass centrilobular nodules, especially in pulmonary veno-occlusive disease. An enlarged pulmonary artery may mimic a mediastinal mass. The hilum convergence sign is helpful to onfirm that the apparent "mass" in fact represents the pulmonary artery. The hilum convergene sign describes the appearance of hilar pulmonary artery branches converging into an enlarged pulmonary artery. In contrast, the hilum overlay sign describes the visualization of hilar vessels through a mass. It indicates that a mediastinal mass is present, which cannot be in the middle mediastinum. Usually this means the mass is in the anterior mediastinum.

Answer 81

The pathologic hallmark of primary pulmonary hypertension (PPH) is the plexiform lesion in the wall of the muscular arteries, which is a focal disruption of the elastic lamina by an obstructing plexus of endothelial channels. There is a relative paucity of prostacyclins and nitric oxide expressed by endothelial cells. PPH may be idiopathic (females \> males) or familial (approximately 10% of cases) On imaging, there is typically enlargement of the main pulmonary arteries with rapidly tapering peripheral vessels.

Answer 82

Congenital left-to-right cardiac shunts, such as ventricular septal defects (VSD), atrial septal defect (ASD), and a partial anomalous pulmonary venous return, cause increased flow through the pulmonary arterial bed. This chronically increased flow may eventually lead to irreversible vasculopathy characterized by pulmonary hypertension and reversal of the congenital shunt, known as Eisenmenger syndrome. Imaging of PAH secondary to a congenital shunt is similar to that of PPH. There is enlargmenet of the central and main pulmonary arteries, with peripheral tapering.

Answer 83

PAH secondary to pulmonary veno-occlusive disease is caused by fibrotic obliteration of the pulmonary veins and venules. Pulmonary veno-occlusive disease may be idiopathic but is associated with pregnancy, drugs (especially bleomycin), and bone marrow transplant. Imaging features pulmonary arterial enlargement. Pulmonary edema and ground glass centrilobular nodules are often present.

Answer 84

Left-sided cardiovascular disease leads to elevated pulmonary venous pressure, which is a cause of pulmonary hypertension. Any left-sided lesion may cause pulmonary venous hypertension, including left ventricular outflow tract lesions, mitral stenosis, and obstructing intra-atrial tumor/thrombus.

Answer 85

COPD, sleep apnea, and interstitial lung disease can all lead to pulmonary hypertension. Chronic hypoxic vasoconstriction is thought to invoke vascular remodeling leading to hypertrophy of pulmonary arterial vascular smooth muscle and intimal thickening. Chronic lung disease can further contribute to obliteration of pulmonary microvascularture through emphysema and the perivascular fibrotic changes of pulmonary fibrosis.

Answer 86

Chronic occlusion of the pulmonary arterial bed can lead to pulmonary arterial hypertension, which is a complication affecting 1-5% of patients who develop acute pumonary embolism (PE). Due to the high prevalence of PE, a PE-protocol CT is typically the first step in workup of newly diagnosed pulmonary hypertension. Characteristic imaging features are peripheral , eccetric filling defects (in contrast to acute emboli which tend to be central) in the pulmonary arterial tree. Fibrous strands are sometimes visible on cross-sectional imaging. Mosaic perfusion may be present. CTEPH may cause secondary corkscrew bronchial arteries that are tortuous and dilated. Treatment of CTEPH is surgical thromboendarterectomy (similar to caroitd endarectomy).

Answer 87

Progressive proliferation of fibrous tissue within the mediastinum may lead to encasement and compression of mediastinal structures. The most common causes of fibrosing mediastinitis are histoplasmosis and tuberculosis. Fibrous encasement of the pulmonary veins leads to permanent histological changes within the endothelial cells. Fibrosisng mediastinitis may also enase the pulmonary artereis, creating a precapillary pulmonary hypertension. Imaging features of fibrosing mediastinitis include increased mediastinal soft tissue, often with calcified lymph nodes due to prior granulomatous infection.

Answer 88

Diagnosis of pulmonary embolism (PE) can be challenging because the presenting symptoms are both common and nonspecific, including dyspnea, tachycardia, and pleuritic chest pain. Most pulmonary emboli originate in the deep veins of the thighs and pelvis. The risk factors for deep venous thrombosis are widely prevalent in a hospital environment, including: (Immobilization, malignancy, catheter use, obesity, oral contraceptive use, and thrombophilia. Approximately 25% of patients with PE don't have any identifiable risk factor.) The Wells score assigns point values to clinical suspicion and various symptoms suggestive of pulmonary embolism. D-dimer is sensitive for thromboembolic disease and has a high negative predictive value, but is of little value in the typical inpatient population as there are many false positives.

Answer 89

CT pulmonary angiogram is the most common method to image for PE, where an embolism is typically seen as a central intraluminal pulmonary artery filling defect. Pulmonary emboli tend to lodge at vessel bifurcations. An eccentric, circumferential filling defect suggests chronic thromboembolic disease. Associated pulmonary abnormalities are commonly seen in patients with PE, including wedge-shaped consolidation, pleural effusion, and linear bands of subsegmental atelectasis. These findings, however, are nonspecific. In particular, pleural effusions and consolidation are seen approximately equally in patients with or without pulmonary embolism.

Answer 90

While a CT pulmonary angiogram is the standard tool to evaluation for pulmonary embolism, it is important to be aware of plain film finding that could suggest pulmonary embolism in case the diagnosis is not clinically suspected. The Fleishner sign describes widening of the pulmonary artereis due to clot. Hampton's hump is a peripheral wedge-shaped opacity representing pulmonary infarct. Westermark sign is regional oligemia in the lung distal to the pulmonary artery thrombus.

Answer 91

Pulmonary embolism may cause acute right heart strain. After evaluation of the pumonary arterial tree, one should always examine the heart for imaging findings of right heart dysfunction. Massive PE may cause acute right ventricular dilation with bowing of the intraventricular septum to the left. An elevated RV:LV ration (caused by RV enlargement) is linearly correlated with increased mortality.

Answer 92

Hilar lymph nodes may simulate a large PE. Cardiac motion causes blurring of the left lower lobe pulmonary arteries, which may simulate small peripheral emboli. Respiratory motion overall decreases accuracy in evaluation of small pulmonary arteries. Mucus-impacted bronchi may simulate PE. Transient disruption fo contrast bolus occurs when onopacified blood from the IVC enters the right atrium and is pumped into the lungs. Unopacified pulmonary veins may simulate PE on a single CT slice; however, one may distinguish between a pulmonary artery and vein by tracing the vessel back to the heart.

Answer 93

The lung has a limited repertoire of responses to injury. Common responses to injury range from recruiting lymphocytes or macrophages, increasing inflammatory debris, and instigating a fibrotic reaction. The idiopathic interstitial pneumonias (IIPs) are seven different patterns of injury response. These patterns can be associated with collagen vascular disease, durg reaction, occupational exposure, or they may be idiopathic. A disease can only be classified as an IIP if there is no other explanation for the pathologic changes. Each of the seven entities has both a clinical syndrome and a separate pathologic diagnossi. Sometimes the clinical syndrome and the pathologic terms have different names and sometimes they share the same name, but in every case there is an acronym. In order to understand the histopathological responses to injury, it is important to review the normal alveolar anatomy.

Answer 94

Idiopathic pulmonary fibrosis (IPF) is the most common idiopathic interstitial pneumonia and has the second-worse prognosis of all, with a mean survival of 2-4 years. The mean survival of IPF is not much different compared to lung cancer. Of all the interstitial pneumonias, only acute interstitial pneumonitis (AIP) has a worse prognosis. Clinical symptoms of IPF include dry cough and dyspnea. IPF usually affects patients \>50 years old. The pathologic diagnosis corresponding to the clinical syndrome of IPF is usual intrestitial pneumonia (UIP), which features interstitial fibroblastic foci and chronic alvolar inflammation. IPF is the clinical syndrome of UIP with unknown cause and is the most common cause of UIP. IPF has a much worse clinical outcome compared to secondary causes of UIP. Other triggers of lung injury that may result in a UIP pattern include: (Collagen vascular disease (rheumatoid arthritis much more commonly than scleroderma), drug injury, Asbestosis. An imaging clue to the presence of asbestosis is calcified plaques indicative of prior asbestos exposure) On imaging, early UIP features irregular reticulation in the posterior subpleural lung bases. In later stages of UIP, reticulation becomes fibrosis, traction bronchiectasis develops, and posterior subpleural honeycombing becomes prominent. The lung bases are most severly affected. The CT diagnosis of late UIP is very specific based on these findings, in particular the presence and posterior basal location of honeycombing. Surgical biopsy can often be avoided if these characteristic imaging features are present.

Answer 95

NSIP is both the name of the clinical syndrome and the corresponding pathologic diagnosis. Affected patients are typically younger (40-50 years old) compared to IPF. Symptoms are similar to IPF with chronic dry cough and dyspnea. Histologically, NSIP features thickened alveolar septa from chronic inflammation. In contrast to IPF/UIP, there is less fibrotic change. NSIP has a better 5-year survival compared to IPF. Unlike IPF, NSIP does respond to steroids. NSIP may be idiopathic or associated with other diseases. NSIP is the most common pulmonary manifestation in patients with collagen vascular disease. (NSIP may also be caused by drug reaction or occupational exposure. NSIP may be associated with dermatomyositis) There are two forms of NSIP. An important imaging feature of NSIP, regardless of the form , is the presence of ground glass opacities (GGO), which are nearly always bilateral. A key feature differentiating NSIP from IPF is the presence of ground glass in NSIP. Fibrotic NSIP predominantly features GGO with fine reticulation and traction bronchiectasis (Honeycombing is usually absent in NSIP. If honeycombing is present, consider UIP. Fibrotic NSIP has a worse prognosis compared to cellular NSIP, but a better prognosis compared to UIP) Cellular NSIP also features GGO, but without significant fibrotic changes (Cellular NSIP is much less common than fibrotic NSIP and has a better prognosis compared to fibrotic NSIP) A key imaging finding (not always seen but very specific) is sparing of immediate subpleural lung. This feature is NOT seen in UIP, and can be seen in both cellular and fibrotic NSIP. Like UIP, NSIP tends to affect the posterior peripheral lower lobes. Other diagnoses should be considered (e.g., chronic hypersensitivity pneumonitis or sarcoidosis) if there is primarily upper lobe disease.

Answer 96

Cryptogenic organizing pneumonia (COP) is the clinical syndrome of organizing pneumonia (OP) without known cause. The clinical syndrome of COP was previously called bronchiolitis obliterans organizing pneumonia (BOOP), which is a term still in general use. COP clincially responds to steroids with a good prognosis and may resolve completely, although recurrences are common. Organizing pneumonia (OP) is the pathologic pattern of granulation tissue polyps that fill the distal airways and alveoli. Organizing pneumonia may be a response to infection, drug reaction, or inhalation. CT of OP shows mixed consolidation and ground glass opacities in a peripheral and peribronchovascular distribution. The reverse halo sign (also known as the atoll sign) is relatvitly specific for OP and features a central lucency surrounded by a ground class halo. (The reverse halo sign should not be confused with the halo sign that is typical of invasive aspergillus, which shows a central opacity with peripheral ground glass)

Answer 97

Respiratory bronchiololitis - interstitial lung disease (RB-ILD) is both the clinical syndrome and the pathologic diagnosis of this smoking-related interstitial lung disease Respiratory bronchiolitis (RB, without the ILD) is very common in smokers, where pigmented macrophages are found in respiratory bronchioles. RB is usually asymptomatic , but if symptoms are present (usually cough and shortness of breath), the clinical syndrome is called RB-ILD. Histologically, RB-ILD is characterized by sheets of macrophages filling the terminal airways, with relative sparring of the alveoli. The key imaging feature of RB-ILD are centrilobular nodules and patchy ground opacities. In contrast to NSIP, the distribution of ground glass in RB-ILD is more random than the peripherally predominant pattern of NSIP.

Answer 98

Like RB-ILD desquamative interstitial pneumonia (DIP) is both the clinical syndrome and the pathologic diagnosis. RB, RB-ILD, and DIP represent a continuous spectrum of smoking-related lung disease. Like RB, brown-pigmented macrophages are invovled in DIP; however, sheets of these abnormal macrophages also extend into the alveoli in DIP. Imaging of DIP shows diffuse basal-predominant patchy or subpleural ground glass opacification, more extensive than RB-ILD. Although the predominant abnormality is ground glass, a few cysts may also be present.

Answer 99

Lymphoid interstitial pneumonia (LIP) is both a clinical syndrome and the pathologic diagnosis. LIP is exceptionally rare as an isolated idiopathic disease and is more commonly associated with Sjogren syndrome or HIV. The histologic hallmark of LIP is diffuse infiltration of the interstitium by lymphocytes and other immune cells, with resultant distortion fo the alveoli. Imaging findings of LIP include diffuse or lower-lobe predominant ground glass. Scattered thin-walled perivascular cysts are often present, which are thought to be due to air trapping from peribronchiolar cellular debris. LIP may be complicated by pneumothorax in advanced disease.

Answer 100

Acute interstitial pneumonia (AIP), synonymous with diffuse alveolar damage (DAD), is the pathologic diagnosis seen in the clinical syndrome of acute respiratory distress syndrome (ARDS). Unlike the other IIPs, AIP is the only syndrome with an acute onset and has the worst prognosis. The primary cause of AIP is surfactant destruction. Two phases of AIP are recognized: Early (exudative) and chronic (organizing). The early (exudative) phase features hyaline membranes, diffuse alveolar infiltration by immune cells, and noncardiogenic pulmonary edema. The chronic (organizing) phase features alveolar wall thickening due to granulation tissue. The chronic phase usually begins one week after the initial injury.

Answer 101

(HSP) is a common lung disease caused by a hypersensitivity reaction to inhaled organic antigens, such as bird proteins or thermophilic actinomycetes, although a history of antigen exposure is not always elicited. HSP is characterized by three distinct phases, from acute to subacute to chronic. Acute HSP is characterized by inflammatory exudate filling the alveoli, which manifests on imaging as nonspecific groundglass or consolidation. Small, ill-defined centrilobular nodules may also be present. The imaging hallmark of subacute HSP is centrilobular ground glass nodules. Mosaic attenuation (geographic areas of relative lucency) and ground glass can also be seen. (mosaic attenuation can be secondary to mosaic perfusion on inspiration and air trapping on expiration. The abnormalities of subacute HSP involve the entire axial cross-section of lung. The head-cheese sign describes the combination of patchy ground glass and areas of lucency due to mosaic perfusion or air trapping.) Chronic HSP, from long-term exposure to the offending antigen, leads to upper-lobe predominant pulmonary fibrosis. Often the findings of subacute disease, including centrilobular nodules, ground glass, and mosaic attenuation, may be superimposed. (unlike IPF, honeycombing is not common in HSP, but when present may involve the upper lobes. If there is relative sparing of the bases, chronic HSP is much more likely than IPF)

Answer 102

A pneumoconiosis is a lung disease secondary to inorganic dust inhalation. In contrast, hypersensitivity pneumonitis is caused by organic dust inhalation. Silicosis and coal workers pneumoconiosis (CWP) are the two most common pneumoconioses. They often have indistinguishable imaging findings even though they are due to different inhaled dusts and have different histologic findings. (Silicosis is due ot inhalation of silica dust, which miners may be exposed to. CWP is caused byy inhalation of coal dust, which does not contain any silica. The most characteristic finding of uncomplicated disease is multiple upper lobe predominant centrilobular and subpleural nodules. Eggshell lymph node calcifications are commonly seen in silicosis, less commonly in CWP. Silicosis or CWP can become complicated with large conglomerate masses or progressive massive fibrosis. Both silicosis and CWP confer an increased risk of TB. Caplan syndrome is seen in patients with rheumatoid arthritis and either CWP or silicosis (more common in CWP) and represents necrobiotic rheumatoid nodules superimposed on the smaller centrilobular and subpleural nodules of the pneumoconiosis.) Asbestosis is lung disease caused by inhalation of asbestos fibers. End-stage asbestosis can lead to pulmonary fibrosis with a UIP pathology (Unlike the other inhalational lung diseases, asbestosis predominantly affects the lower lobes because the asbestos particles are too large to be removed by the alveolar macrophages and lymphatic system. The radiographic/CT appearance and distribution of advanced asbestosis may be indistinguishable from IPF; however, an important clue seen in asbestosis is evidence of asbestos exposure, suh as pleural thickening and plaques. Even though pleural plaques (which may or may not be calcified) are due to asbestos exposure, they are not a component of asbestosis, do not lead to fibrosis, and are usually asymptomatic.)

Answer 103

Simple pulmonary eosinophilia (also known as Loffler syndrome) is characterized by transient and migratory areas of focal consolidation, with an elevated eosinophil count in the peripheral smear. An identical appearance can be seen as a response to injury, especially with parasitic disease and drug reactions. The term simple pulmonary eosinophilia is reserved for idiopathic cases.

Answer 104

Chronic eosionphilic pneumonia is an important consisderation in the differential diagnosis of chronic consolidation. Chronic eosinophilic pneumonia causes extensive alveolar filling and interstitial infiltration with inflammatory esoinophils. Consolidation is patchy and peripheral, with an upper lobe predominance. Unlike simple pulmonary eosinophilia, the pattern of consolidation can remain unchanged for months. Chronic eosinophilic pneumonia responds rapidly to steroids.

Answer 105

Also called allergic angiitis and granulomatosis, Churg-Strauss is a systemic small-vessel vasculitis associated with asthma and periopheral eosinophilia. P-ANCA is positive, which is not very specific. P-ANCA can also be positive in collagen vascular disease and microscopic polyangitis. Imaging findings of Churg-Strauss are varied. The most common appearance is peripheral consolidation or ground glass.

Answer 106

Microscopic polyangiitis is the most common cause of pulmonary hemorrhage with renal failure. P-ANCA is positive. Imaging shows diffuse central-predominant ground glass representing hemorrhage.

Answer 107

Wegener granulomatosis (WG) is a systemic small-vessel vasculitits with a classic clinical triad of sinusitis, lung involvement, and renal insufficiency. C-ANCA is positive, which is very specific for Wegener granulomatosis. In the upper airways, WG may cause nasopharyngeal and eustachian tube obstruction. Involvement of the larynx and bronchi is common, leading to airway stenosis. In the lungs, WGk may cause multiple cavitary nodules that don't respond to antiobiotc theraphy. An intra-cavitary fluid level suggests superimposed infection.

Answer 108

The lung has a diverse but finite repertoire of responses ot injury, including pulmonary edema (due to increased capillary permeability), ARDS, organizing pneumonia, eosinophilic pneumonia, bronchiolitis obliterans, pulmonary hemorrhage, NSIP, and UIP. Pulmonary drug reaction, most commonly to cytotoxic drugs, may elicit any of these injury responses.

Answer 109

Up to 40% of patients develop radiographic abnormalities after external radiotherapy, although most patients are asymptomatic. The radiographic abnormality is largerly confined to the radiation port, usually with non-anatomic linear margins. Radiation pneumonitis is the early stage of radiation injury, which can occur within 1 month of radiotherapy and is most severe 3-4 months after treatment. Radiation pneumonitis features ground glass centered on the radiation port, although extension out of the port is relatively common. Radiation fibrosis is the late stage of radiation injury. Fibrosis becomes apparent approximately 6-12 months after therapy. The key imaging finding is the distribution of fibrosis and traction bronchiectasis within the radiation port, although fibrosis may extend outside the port in 20%.

Answer 110

Sarcoidosis is an idiopathic systemic disorder of noncasseating granulomas that become coalescent to form nodules and masses throughout the body. Pulmonary sarcoidosis may progress to pulmonary fibrosis with honeycombing. Unlike IPF (the most common cause of pulmonary fibrosis), the fibrotic changes of sarcoid have a mid and upper-lung predominance, similar to end-stage hypersensitivity pneumonitis. A historical staging system has been used for radiographic findings (not CT) in sarcoidosis; however, there is not always stepwise progression through the stages. (Stage 0: normal radiograph, Stage 1: Hilar or mediastinal adenopathy only, without lung changes. Stage 2: Adenopathy with lung changes. Stage 3: Diffuse lung disease without adenopathy. Stage 4: End-stage fibrosis) The most common radiographic finding in saroidosis is symmetric adenopathy. Lymph nodes may contain stippled or eggshell calcification in up to 50%. The most common CT finding in sarcoidosis, in addition to adenopathy, is upper-lobe predominant perilymphatic nodules of variable sizes, representing sarcoid granulomas. Bronchial involvement may cause mosaic perfusion due to air trapping. Sarcoiosis may involve other organs, including the spleen, brain, and rarely bone.

Answer 111

PLCH is a smoking-related lung disease - nearly 100% of adults with PLCH are smokers. (The other smoking-relate interstitial lung diseases (aside from emphysema) are RB-ILD and DIP. Multiple smoking-related lung diseases may be present simultaneously) PLCH may present as a spontaneous pneumothorax. Disease is most often isolated to the lungs; however, lucent bone lesions, diabetes insipidus from inflammation of the pituitary stalk (hypophysitis), and skin involvement can occasionally be seen. ( In addition to LCH, the differential diagnosis for disease affecting the lungs and bones includes malignancy, tuberculosis, fungal disease (including blastomycosis, histoplasmosis, and coccidiomycosis), sarcoidosis, and Gaucher disease (pulmonary involvment is rare and may resemble DIP)) The first detectable abnormality is nodules associated with airways. As the disease progresses, the nodules cavitate and resultant irregular cysts predominate. The natural progression is from nodules -\> cavitary nodueles -\> irregular cysts. Radiographic and CT findings include upper lobe predominant cysts and irregular peribronchovacular nodules, both sparing and costophrenic sulci. PLCH is generally steroid responsive and smoking cessation is critical.

Answer 112

Pulmonary alveolar proteinosis (PAP) is an idiopathic disase causing filling of the alveoli with a proteinaceous lipid-rich material. On chest radiogrphy, PAP may resemble pulmonary edema with perihilar opacificatin; however, the heart is normal in size in PAP and pleural effusions are not typically seen. The CT hallmark of PAP is the crazy paving pattern of smooth interlobular septal thickening in areas of patchy or geometric ground glass. Although initially described for PAP, the crazy paving pattern is not specific for PAP, and can also be seen in Pneumocystis pneumonia, cryptogenic orgazinizing pneumonia, bronchoalveolar carcinoma, and lipoid pneumonia, among others. Patients with PCP are susceptible to superimposed infection, classically with Nocardia, which typically presents as a consolidation. Treatment of PAP is bronchoalveolar lavage.

Answer 113

Diffuse cystic lung disease caused by bronchiolar obstruction and lung destruction due to proliferation of immature smooth muscle cells in small vessels, lymphatics, and bronchioles. Approximately 1% of patients with tuberous slcerosis (triad of seizures, mental retardation, and adenoma sebaceum) have a lung disease that is nearly identical to LAM. Almost all cases of sporadic LAM are in women of childbearing age. Some cases respond to anti-estrogen therapy. LAM is associated with pneumothorax and chylous pleural effusion. CT of LAM shows numerous thin-walled lung cysts. In contrast to LCH, the cysts tend to be round and regular. Also LAM affects all five lobes while LCH is upper-lobe predominant.

Answer 114

The anterior mediastinum is the spae between the sternum and the pericardium inferiorly and ascending aorta and brachiocephalic vessels superiorly. The anterior mediastinum can be thought of as two compartments - the prevascular compartment superiorly and the precardiac compartment inferiorly. The contents of the prevascular anterior mediastinum include: (Thymus, lymph nodes, enlarged thyroid gland, if it extends inferiorly into the mediastinum) The precardiac anterior mediastinum is a potential space.

Answer 115

The anterior border of the middle mediastinum is the anterior pericardium and the posterior borders are the posterior pericardium and posterior tracheal wall. The contents of the middle mediastinum include: (Heart and pericardium. Some authors place the heart in the anterior mediastinum. However, for the purpose of differential diagnosis, disease of the heart and pericardium have more in common with the other vascular structures of the middle mediastinum. Ascending aorta and aortic arch. Great vessels including SVC, IVC, pulmonary arteries and veins, and brachiocephalic vessels. Trachea and bronchi. Lymph nodes. Phrenic, vagus, and recurrent laryngeal nerves (all of which pass through the AP window).

Answer 116

The anterior border of the posterior mediastinum is the posterior trachea and posterior pericardium. The posterior border is somewhat loosely defined as the anterior aspect of the vertebral bodies; however, paraspinal masses are generally included in the differential of a posterior mediastinal mass. The contents of the possterior mediastinum include: (Esophagus, Descending thoracic aorta, Azygous and hemiazygos veins, thoracic duct, vagus nerves, and lymph nodes)

Answer 117

Interfaces between anatomic structures in the lungs, mediastinum, and pleura may be displaced or thickened in the presence of a mediastinal mass or abnormality. With the exception of the right paratracheal stripe, it is generally uncommon to see these interfaces in the absence of pathology. (a "line" is a thin interface formed by tissue (typically \<1 mm in thickness) with air on both sides) (A "stripe" is a thicker interface formed between air and adjacent soft tissue) (An "interface" is formed by the contact of two soft tissue structures of different densities) The anterior junction line is formed by four layers of pleura (parietal and visceral pleura of each lung) at the anterior junction of the right and left lungs. (On a frontal radiograph, the anterior junction line is a vertical line projecting over the superior two-thirds of the sternum. Abnormal convexity or displacement of this line suggests an anterior mediastinal mass) The posterior junction line is also formed by four layers of pleura (parietal and visceral pleura of each lung), but at the posterior junction of the right and left lungs. (On a frontal radiograph, the posterior junction line is a vertical line projecting through the trachea on the frontal view, more superior than the anterior junction line. Unlike the anterior junction line, the posterior junction line is seen above the clavicles because the posterior lungs extend more superiorly than the anterior lungs. Abnormal convexity or displacement of this line suggests a posterior mediastinal mass or aortic aneurysm.) The right and left paratrachearl stripes are formed by two layers of pleura where the medial aspect of each lung abuts the lateral wall fo the trahea and intervening mediastinal fat. (The right paratracheal stripe is the most commonly seen of these landmarks, seen in up to 97% of normal PA chest radiographs. Thickening fo the right paratracheal stripe is most commonly due to pleural thickening, although a paratracheal or tracheal mass (including adenopathy or thyroid or traheal neoplasm) can also be a cause. Thickening of the left paratracheal stripe has a similar differential. In addition, however, a mediastinal hematoma should also be considered, especially in trauma.) The posterior tracheal stripe is the only interface seen on the lateral radiograph, representing the interface of the posterior wall of the trachea with the two plerual layers of the medial right lung. The right and left paraspinal lines are actually interfaces but appear as lines due to Mach effect and are formed by 2 layers of pleura abutting the posterior mediastinum. (In contrast to the posterior junction line, the paraspinal lines are located inferiorly in the thorax, typically from the 8th through 12th ribs. A paraspinal line abnormality suggests a posterior mediastinal mass lesion, including hematoma, neurogenic tumor, aortic aneurysm, extramedullary hematopoiesis, esophageal mass, and osteophyte.) The azygoesophageal recess is an interface formed by the contact of the posteromedial right lower lobe and the retrocardiac mediastinum. (The azygoesophageal recess extends from the subcarinal region to the diaphragm inferiorly. Distortion of the azygoesophageal recess may be due to esophageal mass, hiatal hernia, left atrial enlargement, and adenopathy.)

Answer 118

The AP window is a mediastinal space nestled underneath the aortic arch (which forms the superior, anterior, and posterior boundaries) and the top of the pulmonary artery. The medial border of the AP window is formed by the esophagus, trachea, and left mainstem bronchus. On a normal frontal radiograph, the AP window is a shallow concave contour below the aortic knob and above the pulmonary artery. Abnormal convexity (outwards bulging) of the AP window suggests a mass arising from or involving structures that normally live within the AP window, including: (Lymph nodes: Adenopathy is the most common cause of an AP window abnormality. Left phrenic nerve: Injury may cause paralysis of the left hemidiaphragm. Recurrent laryngeal nerve: The AP window should be carefully evaluated in new-onset hoarseness, especially if associated with diaphragmatic paralysis. Left vagus nerve. Ligamentum arteriosum. Left bronchial arteries.) A thoracic aortic aneurysm may also cause convexity of the AP window.

Answer 119

The retrosternal clear space is a normal area of lucency posterior to the sternum seen on the lateral radiograph only. It correlates to the prevascular space on CT. Obliteration of the retrosternal clear space suggests an anterior mediastinal mass, right ventricular dilation, or pulmonary artery enlargement. Increase in the retrosternal clear space can be seen in epmhysema.

Answer 120

The left superior intercostal vein (LSIV) is a normal vein that is not often seen on radiography. When visible, the LSIV produces the aortic nipple, appearing as a small round shadow to the left of the aortic knob on the frontal radiograph. The LSIV may be dilated as a collateral pathway in SVC obstruction.

Answer 121

A better (but considerably less catchy) differential for an anterior mediastinal mass includes: Thymic epithelial neoplasm, such as thymoma if the patient is middle aged or older, or has a history of myasthenia gravis. Less common would be thymic carcinoma. Germ cell tumor, including teratoma, if the patient is a young adult. Thyroid lesion, if there is extension fo the mas above the thoracic inlet. Lymphoma.

Answer 122

Thymoma is the most common primary tumor of the anterior mediastinum and typically occurs in middle-aged or older individuals, between 45-60 years. Thymoma is associated with myasthenia gravis (MG). Approximately 33% of patients with thymoma have MG, and 10% of patients with MG have a thymoma. In addition to MG, thymomas are often associated with other diseases including red cell aplasia, hypogammaglobulinemia, paraneoplastic syndromes, and malignancies such as lymphoma or thyroid cancer. Thymoma can be pathologically classified as low-risk or high-risk based on histology, and non-invasive or invasive based on whether the capsule is intact. (Approximately 30% of thymomas are invasive. If invasive, the tumor may invade adjacent structures including the airways, chest wall, great vessels, and phrenic nerves. Elevation of a hemidiaphragm is suggestive of phrenic nerve invasion. Invasive thymoma may spread along pleural and pericardial surfaces, called drop metastases. However, hematogenous metastases are exceedingly rare.) Thymoma is histologically classifed by the WHO system into A, AB, B1, B2, B3, and C subtypes, with progressively worse prognosis. (Type A tumors are relatively uncommon, but are usually encapsulated. Type B tumors contain increasing number of epithelial cells, which represent the malignant component. Type C represents thymic carcinoma, which may metastasize hematogenously.)

Answer 123

Unlike invasive thymoma, thymic carcinoma is histologically malignant, very aggressive, and often metastasizes hematogenously to lungs, liver, brain, and bone. Prognosis is poor. Distinction between invasive thymoma and thmic carcinoma is difficult on CT, unless there is evidence of distant metastatic disease.

Answer 124

Thymic carcinoid is of neural crest origin. 50% of thymic carcinoids are hormonally active, often secreting ACTH and causing Cushing syndrome. Thymic carcinoid is associated with multiple endocrine neoplasia (MEN) I and II. On imaging, thymic carcinoid is generally indistinguishable from thymoma and thymic carcinoma on CT. If carcinoid is suspected, a preoperative Indium - 111 Octreotide scan can be performed.

Answer 125

A thymic cyst may be secondary to radiation theraphy (e.g., administered to treat Hodgkin disease), may be associated with AIDS (especially when multilocular), or may be congenital. When congenital, thymic cysts arise from remnants of the thymopharyngeal duct. A congenital thymic cyst may occur anywhere along the course of thymic descent from the neck, but most commonly in the anterior mediastinum. Thymic cyst is typically evident on CT as a simple fluid-attenuation cyst in the anterior mediastinum.

Answer 126

Thymolipoma is a benign fat-containing lesion with interspersed soft tissue. It may become quite large and drape over the mediastinum.

Answer 127

Several different types of germ cell tumors may arise in the anterior mediastinum from primitive germ cell elements, most of which are benign. Malignant GCT occurs more commonly in males. Teratoma is the most common anterior mediastinal germ cell tumor, usually encapsulated and predominantly cystic in nature, but fat and calcification are common. A fat/fluid level is specific for teratoma, but is not commonly seen. Teratoma can rarely be malignant, especially if large in size and irregular in shape. Seminoma is the most common malignant anterior mediastinal germ cell tumor. It occurs almost exclusively in men.

Answer 128

Benign and malignant thyroid masses may extend into the mediastinum, including goiter, thryoid neoplasm, and an enlarged gland due to thyroiditis. The key to diagnosis is to show continuity superiorly with the thyroid.

Answer 129

Both Hodgkin disease and non-Hodgkin lymphoma are important differential considerations for an anterior mediastinal mass. Hodgkin disease commonly involves the thorax, most often the superior mediastinal lymph nodes including prevascular, AP window, and paratracheal nodal stations. Non-Hodgkin lymphoma is a diverse group of diseases, which less commonly involve the thorax compared to Hodgkin disease. Calcification is rare in untreated lymphoma.

Answer 130

Lymph node calcification, low attenuation, and avid enhancement are unusual features for lymphoma. An alternative diagnosis should be considered if these imaging findings are seen. Eggshell calcification of lymph nodes is often present in silicosis and coal workers pneumoconiosis, less commonly in sarcoidosis. Given the greater prevalence of saroidosis, however, eggshell calcification may be seen more commonly in sarcoid overall. Dense calcification within a lymph node can be seen in sarcoidosis or as a sequela of prior granulomatous disease. Low attenuation lymph nodes, while nonspecific, should raise concern for active tuberculosis. Low attenuation lymph nodes can also be seen in fungal infection, lymphoma, and metastatic disease. Avid lymph node enhancement can be seen in Castleman disease, sarcoidosis, tuberculosis, and vascular metastases. Avidly enhancing vascular metastases include: (Renal cell carcinoma, thyroid carcinoma, lung carcinoma, sarcoma, melanoma)

Answer 131

Castleman disease, also known as angiofollicular lymph node hyperplasia, is a cause of highly vascular thoracic lymph node enlargement, of uncertain etiology. Localized Castleman disease is seen in children or young adults. Surgical resection is usually curative. Multicentric Castleman disease manifests in older patients or in association with AIDS. Multicentric disease often results in systemic illness including fever, anemia, and lympoma. It is typically treated with chemotherapy. The key imaging finding of Castleman disase is avidly enchancing adenopathy.

Answer 132

A precardiac anterior mediastinal mass is in contact witht he diaphragm. Epicardial fat pad - A prominent epicardial fat pad sihouettes the cardiac border on a frontal radiograph and may simulate cardiomegaly. Pericardial cyst - A pericardial cyst is a benign cystic lesion thought to be congenital. Most are located at the right cardiophrenic angle (between the heart and the diaphragm). Imaging shows a cystic lesion abutting the pericardium, which may change in shape on subsequent studies. Morgagni hernia - Morgagni hernia is a diaphragmatic hernia through the foramen of Morgagni, containing omental fat and often bowel. A Morgagni hernia usually occurs on the right. An anterior mediastinal mass in contact with the diaphragm containing bowel gas is diagnostic for a Morgagni hernia. If the bowel gas is absent, a key to diagnosis on CT is the detection of omental vessels in the mass which can be traced into the upper abdomen.

Answer 133

Lymphadenopathy - Lymphadenopathy is an important cause of a middle mediastinal mass on radiography. Ascending aortic or aortic arch aneurysm - An abnormality of the ascending aorta or aortic arch may appear as a middle mediastinal mass on radiography. Enlarged pulmonary artery (PA) - An enlarged pulmonary artery (PA) can simulate a mass on a chest radiograph. As previously discussed, the hilum convergence sign can help distinguish between an enlarged PA and a mediastinal mass. The hilum convergence sign shows the peripheral pulmonary arteries converging into the "mass" if the mass represents an enlarged pulmonary artery. Foregut duplication cyst - Foregut duplication cysts include bronchogenic cysts, esophageal duplication cysts, and neurenteric cysts. Foregut duplication cysts may occur in the middle or posterior mediastinum.

Answer 134

Neurogenic tumor - A neurogenic tumor may arise from either a peripheral nerve or the sympathetic ganglia. Most adult tumors are peripheral nerve sheath tumors and the vast majority of tumors in children are of sympathetic ganglionic origin. Overall, neurogenic tumors are the most common posterior mediastinal masses. Peripheral nerve tumors (more common in adults) include: Schwannoma (most common), neurofibroma, and malignant peripheral nerve sheath tumor. Sympathetic ganglion tumors (more common in children/young adults) include: Ganglioneuroma (most common), a benign tumor of sympathetic ganglion cells. Neuroblastoma, a malignant tumor of ganglion cells seen in early childhood. Ganglioneuroblastoma, intermediate in histology between ganglioneuroma and neuroblastoma, seen in older children than neuroblastoma. Hiatal Hernia - A hiatal hernia is protrusion of a portion of the stomach through the esophageal hiatus. The esophageal hiatus is an elliptical opening in the diaphragm just to the left of midline. On radiography, air or an air-fluid level is present above the diaphragm. Descending thoracic aortic aneurysm - Thoracic aortic aneurysm may appear as a posterior mediastinal mass on radiography. Extramedullary hematopoiesis - Extramedullary hematopoiesis causes soft tissue paravertebral masses in patients with severe hereditary anemias including thalassemia and sickle cell anemia. The masses are of uncertain origin but may represent herniation of vertebral marrow or may represent elements of the reticuloendothelial system. On imaging, lobulated soft tissue masses are typically bilateral and inferior to T6. Lateral meningocele - A lateral meningocele is lateral herniation of the spinal meninges through either an intervertebral foramen or a defect in the vertebral body. Lateral meningocele is associated with neurofibromatosis. Esophageal neoplasm - Esophageal carcinoma can present on radiography as abnormal convexity of the asygoesophageal recess, mediastinal widening, or a retrotracheal mass. Benign mesenchymal esophageal tumors, such as leiomyoma, fibroma, or lipoma may appear similar on radiography. Foregut duplication cyst - A foregut duplication cyst, a remnant of the fetal foregut, may present as a middle or psoterior mediastinal mass. Paraspinal abscess - A clue to vertebral body pathology on radiography may be paraspinal line displacement.

Answer 135

Relapsing polychondritis - Relapsing polychondritis is a multisystemic disease of unknown etiology characterized by recurrent inflammation of cartilaginous structures. The nose, ear, joints, larynx, trachea, and bronchi can be affected, with airway involvement seen in 50% of patients. (The larynx and subglottic trachea are the most common sites of airway involvement). Relapsing polychondritis usually occurs in middle-aged women. On cross-sectional imaging, there is smooth tracheal/bronchial wall thickening, with sparing of the psoterior membranous trachea. (The tracheal cartilage is an incomplete ring, with no cartilage in the posterior membranous portion.) There is often increased attenuation of the airway wall, ranging from subtly increased attenuation to frank calcification. Tracheobronchopathia osteochondroplastica (TPO) - Tracheobronchopathia osteochondroplastica (TPO) is a benign condition of multiple submucosal calcified osteocartilaginous nodules along the traheal walls. Similar to relapsing polychondritis, there is sparing of the posterior membranous trachea. Tuberculosis - Endobronchial spread of tuberculosis occurs in a prominent minority of patients with pulmonary tuberculosis, mot commonly involving the distal trachea and proximal bronchi. Imaging findings are nonspecific. There is usually smooth concentric narrowing of a relatively long airway segment (typically \>3cm). Amyloidosis - Amyloidosis causes irregular narrowing of the airways due to submucosal amyloid deposition, which may be calcified. Tracheal amyloidosis is very rare. The posterior membranous trachea is not spared. Wegener granulomatosis - Large airway involvement is seen in approximately 20% of patients with Wegener granulomatosis, most commonly manifesting as subglottic tracheal stenosis with circumferential mucosal thickening. The posterior membranous trachea is not spared in Wegener granulomatosis. Sarcoidosis - Tracheal involvement by sarcoid is rare and usually seen in advanced disease. Tracheal sarcoid has a variable appearance ranging from smooth stenosis to a nodular or mass-like appearance. The posterior membranous trachea is not spared in tracheal sarcoidosis.

Answer 136

Intubation/tracheostomy - There is approximately 1% risk of tracheal stenosis after intubation, but approximately 30% risk of stenosis after long-standing tracheostomy. Rare causes of focal tracheal stenosis - Extremely uncommon causes of focal tracheal stenosis include Behcet and Crohn disease.

Answer 137

Bronchiectasis is progressive, irreversible dilation of cartilage-containing bronchi. Three etiologies of bronciectasis have been described, with a final common pathway of mucus plugging, superimposed bacterial colonization, and inflammatory response. (Bronchial wall injury, typically from infection or inflammation, Bronchial lumen obstruction, Traction from adjacent fibrosis). Specific causes of bronchiectasis include: Ineffective clearing of secretions (cystic fibrosis and Kartagener (primary ciliary dyskinesia). Recurrent pneumonia. Bronchocentric infections, such as tuberculosis and atypical mycobacteria. Exaggerated immune response, as seen in ABPA and vasculitis. Impaired immunity: Congenital immunodeficiency, transplant recipients, and agammaglobulinemia. Congenital connective tissue disorders - Mournier Kuhn ( a connective tissue disorder causing tracheobronchomegaly leading to recurrent phemonia), or Williams-Campbell ( a rare disorder of the distal bronchial cartilage, which may be congenital or acquired as a sequela of viral infection)) Cystic fibrosis tends to be upper lobe predominant. In contrast, post-infectious bronchiectasis tends to be lower-lobe predominant. Morphologic classification of bronchiectasis is most useful as a rough gauge of severity. (Cylindrical bronchiectasis (least severe): Mild bronchial dilation. Varicose bronchiectasis (moderately severe): Bronchi may become beaded and irregular. Cystic bronchiectasis (most severe): Bronchi are markedly enlarged and ballooned, with formation of multiple cysts that may not connect to the airways.) Radiographic findings depend on severity. In mild cases only tram tracks may be visible, representing thickened broncial walls causing parallel radiopaque lines resembling tram tracks. In more severe cases there can be extensive cystic change. CT findings include the signet ring sign, which describes a dilated bronchus adjacent to a normal pulmonary artery branch. (Normally each bronchus should be approximately the same size as the adjacent pulmonary artery branch. Other CT findings of bronchiectasis include lack of bronchial tapering, bronchial wall thickening, and mucus-filled bronchi. Often, adjacent tree-in-bud nodules are present, likely representing associated small-airways infection.)

Answer 138

Mnemonic to remember the common causes of bronchiectasis Cystic fibrosis is one othe most common causes of bronchiectasis Allergic bronchopulmonary aspergillosis (ABPA) Post infectious TB/atypical mycobacteria Agammaglobulinemia Immunodeficiency Kartagener Mournier Kuhn

Answer 139

Broncholithiasis is a rare disorder of calcified/ossified material within the bronchial lumen, most commonly caused by erosion of an adjacent calcified granulomatous lymph node. Broncholithiasis clinically presents with nonproductive cough, hemoptysis, and air trapping.

Answer 140

Emphysema is the destruction of alveolar walls resulting in irreversible enlargement of the distal airspaces. Although emphysema initially does not involve fibrosis, end-stage emphysema may lead to a reparative response that ultimately leads to pulmonary fibrosis. Elastase is produced by alveolar macrophages and neutrophils, both of which are incrased in smokers. Elastase is a powerful destructtive enzyme which functions in the host defense mechanism, but excess elastase can be highly harmful to the native tissues. Alpha-1-antitrypsin normally neutralizes elastase. Either a surplus of elastase (in smoking-related emphysema) or a defiency of neutralizing enzyme (in alpha-1-antitrypsin) can cause lung destruction and resultant emphysema.

Answer 141

Centrilobular emphysema is a smoking-related lung disease. Centrilobular emphysema predominantly affects the upper lobes. Like RB-ILD, another smoking related lung disease, centrilobular emphysema primarily affects the center of the secondary pulmonary lobule (All smoking-related lung disease (RB, RB-ILD, DIP, PLCH, and emphysema) may be within the same spectrum of disease caused by macrophage-mediated inflammation in reaction to inhaled particles and toxins.

Answer 142

Paraseptal emphysema is usually seen in combination with other forms of emphysema. It is also smoking related. Paraseptal emphysema is subpleural in location and may predispose to pneumothorax.

Answer 143

Panacinar (also called panlobular) emphysema affects the entire acinus diffusely throughout the lung. The emphysematous changes are usually more severe at the lung bases. Alpha-1-antitrypsin deficiency is an important cause of panacinar emphysema.

Answer 144

Primary tumors of the trachea and central bronchi are rare. In adults, the vast majority of tumors are malignant, while in children most are benign. Squamous cell carcinoma and adenoid cystic carcinoma are by far the two most common primary central airway tumors in adults.

Answer 145

Squamous cell carcinoma is the most common primary tracheal malignancy. It is strongly associated with cigarette smoking. The typical CT appaearance of tracheal squamous cell carcinoma is a polypoid intraluminal mass. The contours of the mass can be irregular, smooth, or lobulated. The tumor can occasionally invade into the esophagus, causing tracheoesophageal fistula.

Answer 146

Adenoid cystic carcinoma (ACC) is a relatively low grade malignancy that usually affects patients in their forties, a decade or two younger than the typical SCC patient. ACC has a propensity for perineural and submucosal spread. Despite indolent growth, metastatic disease tends to have intense FDG uptake on PET imaging. The typical CT appearance of ACC is a submucosal mass that infiltrates the tracheal wall and surrounding mediastinal fat. ACC may also present as circumferential tracheal or bronchial wall thickening causing airway stenosis.

Answer 147

Carcinoid is a spectrum of neuroendocrine neoplasms including low-grade carcinoid, aggressive carcinoid, and small cell carcinoma, featuring a range of biologic behaviors. Carcinoid tumors may rarely secrete hormones such as ACTH. While endobronchial carcinoid is rare in adults, it si the most common bronchial tumor in children. Carcinoid almost always occurs distal to the carina. CT shows an endoluminal bronchial mass with homogeneous arterial enhancement (In addition to carcinoid, the differential diagnosis of an enhancing endobronchial mass includes mucoepidermoid carcinoma and very rare entities such as hemangioma and glomus tumor.)

Answer 148

Mucoepidermoid carcinoma is a rare tumor that originates form tiny salivary glands lining the tracheobronchial tree. Mucoepidermoid carcinoma tneds to affect younger patients than adenoid cystic carcinoma. CT appearance is a round or oval endobronchial mass, indistinguishable from carcinoid.

Answer 149

Tracheal lymphoma is rare. It is usually associated with mucosa-associated lymphoid tissue (MALT), a low-grade malignancy.

Answer 150

Breast cancer, renal cell carcinoma, thyroid cancer, lung cancer, melanoma, and sarcoma are the most common malignancies to metastasize to the central airways. The mnemonic BReTh Lung may be helpful ot remember the four most common airway metastases (breast, renal cell, thyroid, and lung).

Answer 151

Direct central airway invasion occurs more commonly than endobronchial metastases. Aggressive laryngeal, thyroid, esophageal, and lung cancer may cause direct airway invasion.

Answer 152

Papilloma is a benign but potentially pre-malignant lesion tha that may transform into carcinoma. Suspected papillomas are typically closely followed. (A single papilloma is usually caused by chronic irritation. Multiple papillomas (laryngotracheal papillomatosis) are caused by HPV, which may be acquired at birth. Rarely (\<1% of caese), papillomas spread to the lungs, where they may form multiple cavitary nodules.) Chondroma is a benign cartilaginous tumor that rarely may occur in the airways. Other benign endobronchial lesions include schwannoma, adenoma, hamartoma, hemangioma, lipoma, and leiomyoma.

Answer 153

Mesothelioma - Mesothelioma is a highly aggressive neoplasm arising from the pleura. Most cases are due to prior asbestos exposure, with a latency of \>20 years. The epithelial subtype is more common and has a slightly better prognosis. Sarcomatoid and mixed subtypes are more aggressive. CT of mesothelioma typically shows nodular concentric pleural thickening, often with an associated pleural effusion. The role of surgery is evolving, with the goal to resect all visible tumor. Extrapleural pneumonectomy is performed for patients with locally invasive disease. Pleurectomy and decortication is preferred for less advanced disease, where the lung and fissures are spared. Prognosis is equivalent to pleurectomy or pneumonectomy for the less aggressive epithelial subtype. Trimodality therapy involving surgery, intraoperative heated chemotherapy, and radiation has been shown to provide benefit for a subset of patients. Metastases - Lung cancer, gastrointestinal and genitourinary adenocarcinoma, and invasive thymoma can metastasize to the pleura. Multiple myeloma/plasmacytoma - Rib-based lesions may appear to be pleural-based, although the epicenter of a mass arising from a rib will be centered on the rib. Fibrous tumor of the pleura (FTP) - Fibrous tumor of the pleura (FTP) is a focal pleural mass not related to asbestosis or mesothelioma. It is not mesothelial in origin. Approximately 20-30% of FTP are malignant, so all are excised. Malignant potential is determined by number of mitoses seen at pathology. FTP may be associated with hypoglycemia or hypertrophic pulmonary osteoarthropathy, although these associated conditions are uncommon (5%). FTP may be pedunculated. A pleural-based mass that changes position is suggestive of FTP. FTP tends to have low FDG uptake on PET.

Answer 154

Transudate - A transudative effusion is caused by systemic or local imbalances in hydrostatic and oncotic forces. Common causes include systemic low-protein states, heart failure, and nephrotic syndrome. Exudate - An exudative effusion is distinguished from a transudate by thoracentesis. There are no reliable imaging features to distinguish between transudative and exudative effusions. Analysis of the thoracentesis fluid by Light's criteria is the most reliable method to distinguish transudate from exudate. If any one of the following is present, the effusion is classified as an exudate: (Ratio of pleural fluid protein to serum protein \>0.5. Ratio of pleural fluid LDH to serum LDH \>0.6. Plerual fluid LDH \>2/3 upper limits of normal for serum.) The presence of an exudate implies pleural disease causing increased permeability of pleural capillaries, which may be due to: (Pneumonia with parapneumonic effusion, empyema, or tuberculous pleuritis. Mesothelioma or pleural metastasis, Rheumatoid arthritis or other collagen vascular diseases.) Chylothorax - A chylothorax is a pleural effusion consisting of intestinal lymph, most commonly caused by neoplastic obstruction of the thoracic duct. Chylothorax is also associated with lymphangioleiomyomatosis (LAM). The thoracic duct originates at the cisterna chyli in the upper abdomen and drains into the left brachiocephalic or subclavian vein.