Infection Flashcards
1
Q
Pneumonia
A
Community acquried pneumonia: not recently hospitalised or long term care facility >14 d
Hospital acquired pneumonia: >48 hours after admission or <48 hours after discharge
- Segmental/subsegmental consolidation
- Centrilobular nodules/GGO
- +/- cavity
- Pleural effusions/empyema
- Lobe enlargement + buging fissures: Klebsiella
- Pneumatoceles: S.Aureus
- Cavitations: S.Aureus, gram-negative, anaerobes
- Hyperinflation: viral pneumonia
- Children: round pneumonia
- Hilar lymphadenopathy: TB, mycoplasma, fungal
DDx:
- Pulmonary oedema
- ARDS
- COP
- Drug induced lung disease
2
Q
Lung Abscess
A
Pathology:
- Lung necrosis secondary to microbial infection: parenchymal destruction –> scarring –> bronchiectasis –> cyst formation
- Consolidation progressed into cavity over 7-14d
- Complications:
- Empyema
- Bronchopleural fistula –> hydropneumothorax
- Pulmonary gangrene with necrotic lung fragments in abscess cavity (sequestrum), bronchopulmonary fistula
-
Eitiology:
- Aspriation of polymicrobial bacteria from oral cavity
- Primary lung infection: S.Aureus, Klebsiella, S.pyogenes, Type 3 pneumococcus, post transplant or immunosupressed
- Septic emboli
- Malignancy +/- secondary infection (post obstructive)
- Miscellenaeous: direct trauma/neighboring organs/hematogenous seeding
-
Organisms:
-
Anaerobes (-50%)
- peptostreptococcus
- Bateriodes
- Fusobacterium
- Microaerophilic streptococci
-
Aerobes:
- S.auerus
- Klebsiella pneumoniae
- Strep pyogenes
- Hemophilius influenzae
- Actinomyces
- Nocardia
- Mycobacterium: TB/MAC
-
Fungal:
- Asperigillus
- Cryptococus
- Histoplasma
- Blastomyces
- Coccidiodes
- Parasites: Paragonimus,entamoeba
-
Anaerobes (-50%)
Clinical:
- Old
- M>F (4:1)
- High risk: poor entition, seizure disorder, alcoholism, smoker, immunocompromised
Progonosis:
- 33% mortality if untreated
- Heals with scarring, bronchiectasis and cystic change
Rx:
- Antibiotics
- Bronchoscopy if failed treatment –> assess for endobronchial lesion. (not in acude phase for abscesses as potential spillover of contents to normal lung)
- Surgery
- Percutaneous drainage (controversial)
Imaging: CXR/CT
- Location: gravitationally dependent (as often linked to aspiration)
- Irregular, thick-walled, spherical lung cavity with relatively smooth inner margin
- May contain air-fluid level (50%), air, fluid
- Acute angles with adjacent chest wall (unlike empyema)
- +/- surroudning consolidation/GGO (50%)
- +/- pleural effusions (50%) may develop into empyema (33%)
- Bronchogenic spread –> multiple abscesses
- Reactive hilar/mediastinal lymphadenopathy
- Bronchopleural fistula: hydropneumothorax, empyema
- Air-cresent: invasive aspergilosis/mycetoma
- Lemierre disease: pharyngeal infection –> IJ thrombosis –> septic emboli (Fusobacterium)
DDx:
- Pneumatocoele (especially in S.Auerus pneumonia)
- TB: upper lobe consolidation wtih cavitation
- Infected bulla
- Lung Ca
- Septic emboli
- Inflammatory: Wegener, Necrobiotic nodules
- Sequestration
3
Q
Septic Emboli
A
Pathology:
- Infected embolic material seeding from extrapulmonary source
- usually sharply demarcated from adjacent normal lung
- Eitiology:
- IVDU: Staph aureus
- Infective endocarditis
- Lemierre syndrome: fusobacterium
- Infected lines/pacemakers
- Burn patients: p.aeruginosa
- Osteomyelitis
- ICU on broadspectrum AB: fungal
- IDC
Rx: broad spectrum AB, drainage of empyema, treat source of infection
Imaging (radiograph/CT):
- Location: peripheral and basal predominance (blood pool)
-
Multiple descrete nodules
- Cavitation: thick walled, usually lack air-fluid level
- Halo sign: surrounding GGO (gram neg)
- Air bronchograms: gram positive
- Pulmonary infarct: subpleural wedge shaped consolidation
- Feeding vessel sign: vessel leading directily to nodule/wedge-shaped opacity
- +/- Mediastinal lymphadenopathy (20%)
- No intravascular clots
- Plerual effusions/empyema
DDx:
- Pulmonary emboli
- Pneumonia
- Pulmonary mets
4
Q
Pneumococcal Pneumonia
A
Pathology:
- Streptococcus pneumonia: gram positive, 2/3 of bacterial pneumonia
- Colonize nasopharynx –> aerosol inhalation
- Complications:
- Empyema
- ARDS
- Meningitis
- Sepsis
Imaging:
- Lobar consolidation (most common)
- Peripheral
- Airbronchograms
- Surrounding GGO
- Centrilobular nodules/tree-in-bud/GGO in early stages
- Can be round and mass like in children (round pneumonia)
- Parapneumonic effusion (50%) –> look for empyema
- Lymphadenopathy (50%)
- Cavitation + abscess formation rare
DDx:
- Other bacterial pneumonia
- Viral pneumonia
- Aspiration pneumonia/pneumonitis
- Pulmonary hemorrhage
- Cancer
5
Q
Staphlococcus Pneumonia
A
Pathology:
- Staphylococcus (usually s.aureus)
- Community vs hospital acquried
- MRSA common
Imaging:
- Location: multifocal/bilateral
- Patchy/lobar consolidation
- Cavitation/Abscess formation –> heals to form pneumatocoele (may take months to years to resolve)
- Parapneumonic pleural effusions (common) –> empyema
6
Q
Klebsiella Pneumonia
A
Pathology:
- Klebsiella pneumoniae: gram negative bacteria + clear capsule
- High rate of abscess + empyema
- High rate of bacteraemia
- High mortality rate
Imaging:
-
Consolidation/GGO:
- Lobar (can be multilobar)
- voluminous inflammatory exudate
- Bulging fissures (30%)
- Expansion of consolidated lobes
- Pulmonary necrosis
- Sharp margins
- RUL
- Cavitation/abscess: common and occure early
- Pulmonary gangrene: pulmonary vessel thrombosis
- Pleural effusions + empyema
7
Q
Nocardiosis
A
Pathology:
- Nocardiosis Asteroides complex:
- gram positive bacilli
- weakly acid fast
- Slow growth
- PCR is reliable diagnosis
- Immunocompromised (50%)
- Bacteremia –> dissemination to brain (most common), soft tissue, retina
Imaging: Necrotizing cavitary pneumonia
- Unilateral disease
-
Consolidation >> GGO:
- lobar vs diffuse
- Indistinct margins
- Cavitations (40%)
-
Nodules (60%) or Masses (20%)
- Solitary vs multiple
- Well-defined, irregular borders
- Pleural effusion +/- empyema
- Lymphadneopathy
- Bronchiectasis
8
Q
Actinomycosis
A
Pathology:
- Actinomyces: gram positive anaerobic saprophytic organism
- Causes chronic granulomatous inflammation
- Chronic clinical presentation
- Malginancy needs to be excluded
- Association: alcoholism, poor oral hygience, chronic conslidation
IMAGING:
- Focal/pathcy consolidation + central low attenuation
- Peripheral
- Unilateral
- Cavitations
- Pleural effusion
- Chest wall invovlement
- Bronchiectatic form
- Endobronchial actinomycosis –> bronchiolithiaisis/foreign body
- Hilar/mediastinal lymphadenopathy
DDx:
- Malignancy
- Fungal infection
- Other pneumonia
9
Q
Tuberculosis
A
Pathology:
-
Mycobacterium tuberculosis:
- highly aeorbic
- Acid-fast/Ziehl-Neelson stain
-
Caseating granulomatous infection:
- Central caseos necrosis
- Surrounding macrophages, giant cells, lymphocytes
- Ghon Focus: primary site of pulmonary TB causing caeseating granulomatous infection (Lung nodule)
-
Ghon complex: lung nodule + associated lymphadenopathy
- TB drain freely or within phagocytes (with intra-cellular proliferation) from Ghon focus into regional lymph nodes –> ceseating granulomatous reaction in LN
- TH1 Cell-mediated immunity controls infection (takes ~3weeks)
- If heals –> fibrosis + calcification –> RANKE COMPLEX
- Active vs latent: infective vs non-infective
-
TB infection:
-
Primary TB:
- Initial infection of nonsensitized patients
- Progressive primary TB in 5% - elderly/immunocompromised
-
Secondary TB (Post primary):
- Reactivation TB due to impaired immunity
- Exogenous re-infection
-
Miliary TB (primary/secondary may proceed to this)
-
Miliary pulmonary TB
- Hematogenous spread: organism drains via lymphatics –> venous blood –> back to lungs
- Often associated with immunosuppression
- Miliary systemic TB: occurs when there is hematogenous spread via systemic arterial system (liver, bone, spleen, adrenals, meninges, kidneys, uterine tubes)
-
Miliary pulmonary TB
-
Primary TB:
Epidemiology:
- 1/3 of popoulation infected
- Highest prevance: India, China, South Africa, Indonesia, Pakistan
Primary pattern:
- Consolidation: segmental, lobar, multifocal
- Atelectasis (children)
- Lymphadneopathy: central, low attenuation with enhancing rim
Primary Progressive:
- Consolidation +/- Cavitation
- Acute bronchogenic dissemination/bronchiolitis:
- Tree-in-bud
- Centrilobular nodules
- Lobular consolidation/GGO
- Lymphadenopathy
Secondary/Post primary:
- Upper lobe predominant: apical/posterior segments
- Heterogenous consolidation: lobular/segmental/lobar, multifocal
- Cavitation (45%): may erode into airways
-
Bronchiolitis:
- Tree-in-bud
- Centrilobular nodules
- Lobular consolidations/GGO
-
Air-way invovlement:
- Bronchial stenosis
- Bronchial wall thickening
- Volume loss/hyperinflation/postobstructive pneumonia
- Tracheal/laryngeal invovlement (less common)
-
Nodules (tuberculomas):
- Dominant lesion + satelite nodules
- Calcifications
- Pleural effusions
- Lymphadenopathy (5%): pre-existince of hypersensitivity means that prompt and marked tissue response occurs that wall of foci of infeciton, prevents lymphatic spread
Complications:
- Miliary TB: hematogenous spread –> random nodules
- Tuberculous empyema
- Mycetoma
-
Hemoptysis:
- Rasmussen aneurysm (pulmonary artery pseudoaneurysm)
- Hypertrophied bronchial arteries
- ARDS
-
other:
- Lung fibrosis
- Nediastinal fibrosis
- Endobronchial/endotracheal involvement: bronchostenosis, broncholithiasis
- Malignancy
- Hematogenous/lymphatic spread:
- Organ invovlement:
- Pott disease (discitis/osteomyelitis)
- Meningitis
- liver/spleen/adrenals/uterine tubes etc
- Lymphadenities (scrofula)
- Organ invovlement:
Diagnosis: isolation and culture of MTB
Rx: isoniazid, rifampicin, streptomycin, ethambutol, pyrazinamide
DDx:
- Sarcoid
- Chronic fungal infection
- Lung Ca
- PMF
- Ankylosing spondylitis
10
Q
Nontubercululous Mycobacterial Infection
A
Pathology:
-
Mycobacterium Avium or Intracellulare complex (MAC)
- Acid-fast bacilli within macrophages
- May be disseminated throughout phagocyte sytem (LN, liver, spleen, localised to lungs)
- Source: water
- Cause granulomatous infection
- Typically in T-cell immunodeficiency: disseminated infections
- Atypically immunocompetent: tend to be isolated to lungs
Imaging:
- General Features:
- Slowly progressive bronchiectasis, nodules
- Location: Middle lobe + lingular
-
Cavitary form (classic): INDISTINGUISHABLE FROM TB
- Upper lobe predominance
- Cavitation (thin-walled)
- Pleural thickening
- Consolidation/GGO/nodules/mass-like opacities
- Bronchiolitis: centrilobular nodules, tree-in-bud
- Lymphadenopathy
-
Bronchiectatic form (nonclassic)
- Middle lobe/lingula bronchiectasis
- Bilateral mutltifocal Bronchiolitis: tree-in-bud, centrilobular nodules, bronchial wall thickening, mucous plugging
- Perbronchial nodules
- Consolidation/GGO
- Mosaic attenuation (small air-way disease)
- Scarring, volume loss, archiectural distortion
- Nodules
-
Immunocompromised:
- hilar/mediastinal lymphadneopathy
- Pleural effusions
- Hypersensitivity pneumonia: airtrapping + centrilobular nodules
DDx:
- TB
- Other infection: cryptococcus, sporotrichosis, nocardiosis
- Lung cancer
- PMF
11
Q
Mycoplasma Pneumoniae
A
Pathology:
- Mycoplasma pneumoniae
- Oedema/inflammatory cellular infiltrate in alveolar septa/peribronchovascular interstitium
- Spread by respiratory droplets
- Children + young adults (15-50% of pneumonias)
CT
- Lower lobe predominance
- Uni vs bilateral
- Patchy consolidation
- Bronchilolitis: centrilobular/peribronchovascular nodules/GGO, tree-in-bud, bronchial wall thickening
- Lymphadenopathy
- Small pleural effusions
Complications:
- Pericarditis
- Swyer-James-Mcleod syndrome
- Bronchiectasis
Rx: macrolides/quinolones, supportive
12
Q
Influenza Pneumonia
A
Influenza A/H1N1: lower respiratory tract viral infection
Radiograph:
- Interstitial opacities
- Nodular opacities
- Extensive air-space disease
- Progression to ARDS
CT:
- Mosaic attenuation + air-trapping
- GGO/Consolidation
- Bronchiolitis: centrilobular nodules/GGO/consolidation, tree-in-bud
13
Q
CMV pneumonia
A
Cytomegalovirus
Immunocompromised
General:
- Diffuse or lower lung predominance
Radiograph:
- Bilateral patchy or diffuse opacities
- Small or large lung nodules
- Consolidation: segmental/lobar
- Plerual effusion
CT:
- Consolidation: may be mass-like
- Patchy or diffuse GGO
- Nodules: random, bilateral
- Bronchiolitis: tree-in-bud, bronchial wall thickening
- Pleural effusions
DDx:
- PCP
- Viral pneumonia
- Drug reaction
- Lung transplant rejection
14
Q
Histoplasmosis
A
Pathology:
- Histoplasma capsulatum: fungus found in soil
- Acquired by inhalation of dust particles from soil contaminated with bird/bad troppings containing spores
- Found mainly in phagocytes and form a granulmoatous infection –> fibrose and calcify
- Disease process is similar to TB:
- Primary pulmonary invovlement that is often self limiting (produce coin lesions)
- Chronic progressive secondary lung disease
- Extrapulmonary spread
- Diseeminated disease in immunocompromised
Rx:
- Immunocompentent: resolves without treatment (99%)
- Immunocompromised: antifungal
Imaging:
-
Acute histoplasmosis:
- Airspace disease in any lobe/multifocal, lower lobe predominant
- Ipsilateral hilar/mediastinal lymphadenopathy
- Plerual/pericardia leffusion + caviatation
-
Chronic histoplasmosis:
- Progressive upper lobe patchy opacities
- volume loss
- fibrosis/honeycombing
- Emphysema/bullae
- Disseminated disease: miliary nodules +/- cavitation
-
Histoplasmoma:
- nodule +/- calcification (diffuse/central/laminated)
- lung + mediastinum
- Ipsilateral hilar/mediastinal lymphadenopathy + calcification (mimics ranke complex)
- May be centrally necrotic
- Fibrosing mediastinitis: soft tissue infiltration, causing narrowing of adjacent structures
- Calcified hepatic/splenic granulomas
- Broncholith
- Middle lobe syndrome
Fluoroscopy: evaluate esophageal stenosis, fistula, diverticula
DDx:
- TB (very similary)
- Malignancy
- Other fungal infection
15
Q
Coccidioides Immitis
A
Pathology:
- Inhalation of arthroconidia (type of spore) of Coccidioides immitis (fungus)
- Delayed type hypersensitivity reaction –> granulomatous lesions (similar to histoplasma)
- Incubation period 1-4 weeks
- Asymptomatic (90%)
- Symptomatic (10%) lung lesions/fevers/cough
- Disseminated disease (<1%): immunosuppressed
Epi: endemic to arid regions of western hemisphere
Rx: amphotericin B if severe symptoms
Imaging:
- Lobar consolidation/lung nodules (thick/thin grape skin walls) + cavitation
- Hilar/mediastinal lymphadenopathy
- Pleural effusion
- immunocompromised
DDx:
- Bacterial
- Fungal
- Mycobacterial
- Cancer
