Respiratory - Imaging Flashcards
What is the appearance of cardiomegaly on CXR?
The heart is abnormally large. It takes up greater than 50% of the internal width of the thorax.
What are the causes of cardiomegaly?
1) Hypertrophy - caused by an increase in afterload on a particular chamber (e.g. aortic stenosis, hypertension)
2) Dilatation - secondary to toxic, metabolic or infectious agents causing myocardial damage
Hypertrophy of either ventricle does not usually enlarge the heart shadow unless there is synchronous dilatation. Cardiomegaly is usually abnormal, except in athletes, and is associated with other cardio vascular pathology.
How does pulmonary oedema appear on an X ray?
The heart border can be enlarged or normal. There is increased shadowing spreading out from the hilar (enhanced lung markings). Pulmonary oedema occurs when fluid leaks into the lung interstitium from the pulmonary vasculature, leading to impaired gas exchange. It is caused by either:
i) an increased vascular hydrostatic pressure (e.g. cardiogenic causes - LVF, mitral stenosis)
ii) decreased plasma oncotic pressure - liver failure, renal failure
iii) increase in pulmonary capillary membrane permeability - ARDS, aspiration, inhalation injury, multiple blood transfusions
What are the chest x ray features of non cardiac pulmonary oedema?
Normal heart size
Diffuse alveolar shadowing
What are the x ray features of cardiogenic pulmonary oedema?
ABCDE signs: Alveolar shadowing (bats wings) Kerley B lines Cardiomegaly Upper lobe Diversion Effusion
Why does upper lobe diversion occur in cardiogenic pulmonary oedema?
The upper lobe vessels are normally narrower than the lower lobe vessels. In cardiogenic pulmonary oedema, lower zone alveolar hypoxia causes arteriolar vasoconstriction, diverting blood to the upper lobes.
What are Kerley B lines?
These represent oedema of the interlobular septa and are characteristic of pulmonary oedema. They are 1cm long, thin, horizontal and parallel and seen peripherally above the costophrenic angle.
What are the features of pleural effusion on CXR?
Blunting of the costophrenic angles, meniscus and a “white out” (large effusions) are classic features.
What are the main types of pleural effusion?
Aspiration allows biochemical division into transudates (<30g/L of protein) and exudates (>30g/L). Transudates are caused by LV failure, pulmonary embolism and cirrhosis. Exudates are caused by infection, neoplasia and inflammatory conditions - e.g. rheumatoid arthritis or SLE. CXR may point to the cause - e.g. enlarged heart shadow, lung mass, parenchymal disease, apical fibrosis or bone metastases. Effusions collect in gravity dependent areas.
How can you tell from a chest X ray that a patient had cardiac surgery as an adult?
Adults have radio-opaque sternotomy clips, whereas children have ties that are not visible on X ray. Other signs include mechanical prosthetic heart valves which are more radio-opaque than biologic ones.
How do pleural plaques appear on chest X rays?
Pleural plaques are focal areas of pleural fibrosis caused by previous exposure to asbestos. Pleural calcification is a late sign, occurring in approximately half of those with asbestos related disease. It is most easily seen along the diaphragmatic pleura as a layering of dense material.
Classic X ray features include a widespread distribution of opacification, peripheral pleural thickening and pleural calcific deposits.
What are the features of lobar consolidation on chest X ray? What can cause it?
Consolidation is a pathological process caused by filling of the alveolar air spaces with fluid or debris, such as:
i) inflammatory exudate - e.g. pneumonia
ii) haemorrhage - e.g. trauma, vasculitis or PE
iii) transudates
iv) secretion - alveolar proteinosis and mucus
v) malignancy - carcinoma, lymphoma
Key features are “fluffy” airspace density, and air bronchograms. The fluffy air space opacification is not well demarcated unless bordered by a pleural margin, e.g. a fissure or lung edge.
What is atelectasis?
Atelectasis is the incomplete expansion of lung tissue affecting a section or whole of one lung. It is usually not life threatening as the normal lung can compensate for functional loss and the atelectatic area usually re expands once the cause is treated. CXR features can be difficult, there are focal light grey densities and volume loss.
What are the causes of atelectasis?
Obstructive - foreign body, tumour or mucous plug may obstruct a large or small bronchus, leading to lobar or lung collapse
Non obstructive - a reduction in surfactant production may be the cause of the atelectasis in ventilated patients or ARDS. Surfactant reduces alveolar surface tension and helps splint the alveoli open. Post-operative diaphragm dysfunction is a common cause of atelectasis of the lung bases. Other non obstructive causes include lung fibrosis and loss of contact between the parietal and visceral pleura - e.g. effusion or pneumothorax, compromising lung expansion
What are the chest x ray features of bronchiectasis?
Bronchiectasis is a difficult diagnosis to make with any great certainty on plain X ray imaging. The diagnosis is made accurately on high resolution CT. CXR does however demonstrate serious disease and therefore remains the first line investigation for suspicious symptoms such as persistent cough, profuse purulent sputum and recurrent infections.
Suggestive features include:
1) Ring opacities - end on bronchi with thickened walls appear as circular light grey densities with black centres, resembling rings
2) Tram tracks - side on dilated bronchi with thickened walls appear as light grey parallel lines
3) Cystic spaces - these occur in cystic bronchiectasis and appear as circular light grey densities looking like thin walled ring opacities - may contain air fluid level
4) Crowding of pulmonary vascular markings - mucous obstruction of peripheral bronchi can cause atelectasis. The loss in lung volume brings the vascular markings closer together
