Sun14November1246PM 4

On the posteroanterior (PA) chest x ray:

True / False

It is taken at full expiration where possible Correct

The pulmonary vessels behind the heart are almost never visualised Incorrect answer selected

Bowel interposed between the liver and the right hemidiaphragm is a rare variant Correct

The left hemidiaphragm is usually about 2 cm higher than the right Correct

Rotation of the patient causes the lungs to have a difference in translucency Correct

Explanation

The PA chest x ray is performed in the radiology department and is a high quality radiograph, which differs from the portable anteroposterior (AP) chest x ray which is of inferior quality.

The technique of taking a PA chest x ray involves a patient standing with their back to the x ray source, with the anterior chest wall against the film plate. It should ideally be taken at full inspiration, otherwise the appearance of abnormal lung base shadowing and cardiac enlargement may be seen.

When the x ray penetration is sufficient the thoracic vertebrae can be visualised on the radiograph, which ensures that the pulmonary vessels behind the heart are well seen.

In an adequately centred x ray, the medial ends of the clavicles should be equidistant from the spinous processes in the midline of the thoracic spine. If the patient is rotated then it can cause the lungs to have a difference in translucency, which can mimic pulmonary disease. The hilum and heart may also look enlarged.

Normally the right hemi diaphragm is higher than the left by 1.5-2 cm and a difference of more than 3 cm may be significant. In hyperinflation they may be at the same level and when the stomach or splenic flexure is distended the left hemidiaphragm may be higher than the right.

Rarely, bowel may be interposed between the liver and the right hemidiaphragm and this is known as Chilaiditi's syndrome.

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Times answered: 238