Chest x-ray and PET

Question 1

What is a chest x-ray?

Answer 1

Chest X-rays produce images of your heart, lungs, blood vessels, airways, and the bones of your chest and spine. Chest X-rays can also reveal fluid in or around your lungs or air surrounding a lung.

Question 2

What is the systemic approach to CXR interpretation?

Answer 2

Patient details and date 
Technical quality 
Trachea 
Heart and mediastinal contours
Lung fields and pleura 
Diaphragms 
Bones

Question 3

Patient details and date

Answer 3

Note the patient’s name and DOB as well as the date and time the CXR was performed.
This is to ensure that the correct film was identified.

Question 4

Technical quality

Answer 4

Orientation- Most CXRs are taken using a PA view. If the patient is too unwell to stand, then an AP CXR will be done.

Posture- If the patient is supine, the distribution of air and fluid is changed and it is impossible to exclude pneumothorax, pleural effusion or subdiaphragmatic air.

Rotation-The sternal ends of the clavicles should symmetrically overlie the transverse processes of the 4th or 5th thoracic vertebrae.
If the patient is not rotated, the spinous processes of the thoracic vertebrae will be projected midway between the medial borders of the clavicles.

Penetration- The thoracic vertebral bodies should be just visible behind the heart.

Inspiration- There should be 5-7 ribs visible anteriorly (or 10 posteriorly)
Hyperinflation- COPD

Field of view: All of the lungs should be visible, make sure the lung apices and especially costophrenic angles have not been missed.

Exposure- An under-exposed image will be too white and over-exposed image will be too black

Question 5

Trachea in the systematic approach

Answer 5

The trachea should be central.
It may deviate towards an area of loss volume (lobar collapse), or away from an area of increased pressure (tension pneumothorax)

Question 6

Mediastinal contours and hilum

Answer 6

Superior mediastinum: a central widening may represent a normal variant (as you age), aortic aneurysm or soft tissue mass (thymoma)
There are 3 bulges normally visible on the left border of the mediastinum that help identify pathology if abnormal.
Hila: shadows cast by the pulmonary arteries and veins. The left hilum is usually higher than the right. The hila may be pulled up or down by fibrosis or collapse.

Question 7

Heart in the systemic approach

Answer 7

A cardiac shadow of >50% of the total thoracic width on a PA film is abnormal.
This occurs with ventricular dilatation or pericardial effusion.
Left heart border consists of the left ventricle and left atrium.
The right heart border is made up of the right atrium.
Consolidation in the immediately adjacent lung blurs the heart borders.

Question 8

What can cause an enlarged hilum?

Answer 8

Pulmonary arterial HTN
Bronchogenic ca
Lymph nodes
Sarcoidosis, TB and lymphoma can give bilateral hilar lymphadenopathy.

Question 9

What can cause a calcified hilum?

Answer 9

Sarcoid
Past TB
Silicosis
Histoplasmosis

Question 10

Lung fields in the systematic approach

Answer 10

Assess and compare the upper, middle and lower zones of both lungs.
Normal ‘lung markings’ are the shadow cast by branching intrapulmonary blood vessels so the size of normal lung markings decreases with distance from the hilum.

Question 11

Pleura in the systematic approach

Answer 11

Not normally visible on a CXR.
A pleural thickening appears on the CXR as a dense line on the inner surface of the lateral chest wall.
Thickened pleura forms a cap that opacifies the first intercostal space on the X-ray.
Thickened pleura occur after:
Emphysema
Pleurodesis
Industrial exposure to asbestosis

Question 12

Diaphragm in the systematic approach

Answer 12

The right side is often slightly higher (due to the liver).
Causes of raised hemidiaphragm:
Trouble above the diaphragm- Lung volume loss or inflammation
Trouble with the diaphragm- stroke, phrenic nerve palsy
Trouble below the diaphragm- hepatomegaly, a subphrenic abscess.

Question 13

What is opacification?

Answer 13

Lung opacities are described as nodular, reticular (a network of fine lines, interstitial) or alveolar (fluffy).
A single nodule may be called a space-occupying lesion (SOL)

Question 14

What is a lung nodule?

Answer 14

Lung nodules are small growths on the lungs. They are very common, can be benign or malignant, and often do not cause symptoms.

If the nodule is >3 cm across, the term pulmonary mass is used instead.

Question 15

Causes of lung nodules

Answer 15

Neoplasia- metastases (often missed if small), lung cancer, hamartoma, adenoma.
Infections- Varicella pneumonia, septic emboli, abscess, hydatid
Granulomas- miliary TB, sarcoidosis, histoplasmosis
Pneumoconioses (except asbestosis), Caplan’s syndrome.

Question 16

What is reticular opacification?

Answer 16

Lung parenchymal changes
Causes include:
Acute interstitial oedema
Infection: acute (viral, bacterial), chronic (TB, histoplasmosis)
Fibrosis: usual interstitial pneumonia (UIP), non-specific interstitial pneumonia (NSIP), drugs (methotrexate, bleomycin, crack cocaine), connective tissue disorders (rheumatoid arthritis, SLE, PAN, systemic sclerosis, sarcoidosis), industrial lung diseases (silicosis, asbestosis)

Question 17

What is alveolar opacification?

Answer 17

Airspace opacification can be due to any material filling the alveoli.
Causes include:
Pus-pneumonia
Blood- haemorrhage, DIC
Water- heart, renal or liver failure, ARDS, smoke inhalation, drugs (heroin), O2 toxicity, near-drowning.
Cells- lymphoma, adenocarcinoma
Proteins- alveolar, proteinosis, ARDS, fat emboli (7 days post fracture)

Question 18

What is the silhouette sign?

Answer 18

Normal adjacent anatomical structures of differing densities form a crisp contour or ‘silhouette’.
Loss of a specific contour can help determine the position of a disease process.
This phenomenon is known as the silhouette sign.

Question 19

What are the causes of linear opacities?

Answer 19

Septal lines (Kerley B lines i.e interlobular lymphatics seen in fluid, tumour or dust
Atelectasis 
Pleural plaques (asbestos exposure)

Question 20

Causes of gas outside the lungs

Answer 20

Check for a pneumothorax (hard to spot if apical or in a supine image)
Surgical emphysema (trauma, iatrogenic)
Gas under the diaphragm (surgery, perforated viscus, trauma)
Pneumomediastinum: Air tracks along mediastinum, into the neck.
Due to the rupture of the alveolar wall (asthma)

Question 21

Bones abnormalities on CXR

Answer 21

Check the clavicles for fracture
Ribs for fractures and lesions (e.g. metastases)
Vertebral column for degenerative disease, collapse or destruction and
Check shoulders for dislocation, fracture and arthritis.

Question 22

How does PET scan work?

Answer 22

• A tracer such as F-fluorodeoxyglucose (a short half-life glucose analogue-FDG) is taken
• This becomes concentrated in metabolically active tissues
• FDG decays rapidly to produce a positron which collides with electrons to produce protons which PET detects.
• There’s normal high uptake of FDG which occurs in brain, liver, kidney, bladder, larynx and lymphoid tissue and this must be considered.

Question 23

How does PET detect neoplasms?

Answer 23

High uptake of FDG with hotspots suggests primary disease or metastases.
There’s a risk of false-positive when there’s an inflammatory lesion (TB and sarcoid).
PET allows staging of many solid organ malignancies (lung, melanoma, oesophageal) as well as lymphomas.

Question 24

Other uses of PET

Answer 24

Image occult sources of infection