Chest & Cardiac Imaging — Practice

Question 1

An opacity obscures the left heart border but the left hemidiaphragm remains sharp. The lesion is in the

Accepted Answer

B

Question 2

The presence of an air bronchogram within an opacity indicates

Accepted Answer

B

Question 3

A breathless patient has a homogeneous opacity occupying the left hemithorax with the trachea deviated toward it. Interpret.

Accepted Answer

The trachea moving toward the abnormality indicates volume loss, so this is collapse rather than a simple effusion.

A large pleural effusion adds volume and pushes the mediastinum away. Collapse removes aerated volume, so everything is pulled toward it: trachea and mediastinum shift ipsilaterally, the hemidiaphragm rises and the ribs crowd.

The important inference is causal. Complete collapse of a lung in an adult implies obstruction of the main bronchus, and the commonest causes are bronchogenic carcinoma, a mucus plug or an inhaled foreign body.

A combination is also possible and is a specific trap. An effusion with mediastinal shift toward it means there is collapse as well, usually from an obstructing tumour, and attributing everything to the effusion would miss the lesion causing it. CT and bronchoscopy follow.

Question 4

A hypotensive trauma patient has absent breath sounds on the right with tracheal deviation to the left. A junior doctor requests a chest radiograph. Comment.

Accepted Answer

The film should not be waited for. This is tension pneumothorax, a clinical diagnosis, and the immediate treatment is decompression followed by intercostal drain insertion.

The pathophysiology explains the urgency. A one-way valve allows air into the pleural space without escape, so intrapleural pressure rises progressively, collapsing the lung, shifting the mediastinum, kinking the great veins and reducing venous return. Death results from obstructed cardiac filling rather than from hypoxia alone.

Waiting for radiographic confirmation is a recognised cause of avoidable death, and delay in a hypotensive patient can be measured in a few minutes before arrest.

The corollary is worth noting: on a supine film, as most trauma films are, pleural air collects anteriorly rather than apically and may show only a deep sulcus sign, so the film can be falsely reassuring even when obtained.

Question 5

A portable anteroposterior film in a ventilated patient is reported as showing cardiomegaly. Comment.

Accepted Answer

Cardiomegaly cannot be diagnosed on an anteroposterior film, and this report should not be acted on.

The cardiothoracic ratio threshold of 0.5 assumes a posteroanterior projection taken with the patient upright at a standard distance. In that arrangement the heart, which lies anteriorly, sits close to the detector, so magnification is minimal.

On an anteroposterior film the beam enters from the front and the heart lies further from the detector, so it is magnified. Portable films also use a shorter focus-to-film distance, which magnifies further, and supine positioning increases venous return and pulmonary blood volume, broadening the mediastinum.

The practical rule is that an AP film can exclude a large heart if the ratio is normal, but an apparently enlarged heart requires a proper posteroanterior film or echocardiography before the finding is accepted.

Question 6

A patient with advanced HIV has cough and fever with a normal-looking chest radiograph. Can pulmonary tuberculosis be excluded?

Accepted Answer

No. In advanced HIV with significant immunosuppression, the classical radiographic appearances of tuberculosis break down.

Cavitation depends on a vigorous cell-mediated immune response that liquefies caseous material, and as CD4 counts fall that response is lost, so cavities become less common. Instead the pattern shifts toward lymphadenopathy, lower zone involvement, miliary spread and, importantly, a chest radiograph that may look entirely normal despite culture-positive pulmonary disease.

The clinical consequence is that a normal film does not exclude tuberculosis in this population, and sputum testing is performed regardless. Nucleic acid amplification testing with rifampicin resistance detection is the appropriate first-line investigation, since it is rapid, sensitive in this setting and simultaneously identifies drug resistance.

The wider lesson is that radiographic patterns describe the host response as much as the organism, so any condition altering that response alters the picture.

Question 7

A 30-year-old has an anterior mediastinal mass on chest radiograph. Outline your differential and how you would proceed.

Accepted Answer

The anterior compartment differential is conventionally remembered as the four Ts: thymoma and other thymic lesions, teratoma and other germ cell tumours, thyroid extending retrosternally, and terrible lymphoma.

Age shifts the probabilities. In a 30-year-old, lymphoma and germ cell tumour lead, whereas thymoma is commoner beyond middle age.

History and examination narrow it further. Ask about myasthenic symptoms, since thymoma associates with myasthenia gravis and also with red cell aplasia and hypogammaglobulinaemia. Ask about B symptoms and examine for peripheral lymphadenopathy for lymphoma. Examine the testes and check alpha-fetoprotein and beta human chorionic gonadotropin for germ cell tumour, since these can be diagnostic without biopsy and are markedly raised in non-seminomatous tumours.

Contrast CT of the chest characterises the mass, defines vascular relations and identifies fat or calcium suggesting teratoma. Tissue is then obtained, with the important caveat that a large anterior mediastinal mass can cause airway or vascular collapse under general anaesthesia, so the airway is assessed before any procedure requiring sedation.

Question 8

A patient with reduced ejection fraction has cardiac MRI showing mid-wall late gadolinium enhancement not conforming to any coronary territory. What does this mean?

Accepted Answer

This is a non-ischaemic pattern of scar, and it effectively excludes infarction as the cause of the cardiomyopathy.

The reasoning rests on how myocardial infarction damages tissue. Coronary perfusion runs from epicardium to endocardium, and the subendocardium is furthest from the supply and has the highest wall stress, so it dies first. Infarct scar therefore always involves the subendocardium and extends outward to a variable degree, and it is confined to the territory of a coronary artery.

Enhancement in the mid-wall, sparing the subendocardium and crossing territorial boundaries, cannot have been produced by coronary occlusion. It indicates a non-ischaemic process, with dilated cardiomyopathy, myocarditis, sarcoidosis and infiltrative disease among the possibilities, and the specific distribution helps distinguish between them.

The clinical importance is direct. It tells the team that revascularisation will not help, redirects investigation toward causes of non-ischaemic cardiomyopathy, and carries prognostic weight, since the presence and extent of mid-wall fibrosis predicts arrhythmic risk and informs decisions about defibrillator implantation.

Question 9

A ventilated patient desaturates suddenly. The film shows opacification of the left hemithorax with the endotracheal tube tip beyond the carina on the right. Explain.

Accepted Answer

The endotracheal tube has migrated into the right main bronchus, so the left lung is not being ventilated and has collapsed.

The anatomy explains why it is nearly always the right. The right main bronchus is wider, shorter and more vertical than the left, so a tube advanced too far follows it preferentially. The tip should sit a few centimetres above the carina precisely to allow a margin of safety.

Movement is expected rather than exceptional. The tube advances with neck flexion and withdraws with extension, by a centimetre or two in each direction, so a tube that was correctly placed can migrate with repositioning, transfer or physiotherapy.

The consequence is complete collapse of the unventilated left lung, producing sudden desaturation, absent left-sided breath sounds and a white left hemithorax with volume loss. Management is immediate withdrawal of the tube to the correct depth with re-auscultation, after which the left lung usually re-expands, and a repeat film confirms both tube position and re-aeration.

Practice — Chest & Cardiac Imaging

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