Pleural Effusion

PLEURAL EFFUSION

PLEURAL EFFUSION –BASIC ANATOMY

The pleura can be likened to a sac enveloping the lung. This sac has two membranous walls – the inner visceral and the outer parietal.

The pleura is not visible on a normal CXR except where it forms part of a lung Fissure or where the two lungs abut each other in the midline.

The pleural space is a closed cavity between the layers of the visceral and parietal pleura.

A small amount of lubricating fluid lies within the cavity. The lung fissures extend between the lobes of each lung and are lined by two layers of visceral pleura.

EVALUATION OF PLEURAL EFFUSION IN CHEST X-RAY

Fluid in the pleural space can adopt several different appearances on both erect and supine CXRs.

• On the erect frontal CXR

The commonest appearance is an opaque meniscus at a costophrenic angle.

It requires approximately 200–300 ml of pleural fluid to efface the normal sharp recess between the diaphragm and the ribs.

If the effusion is very large, then the entire hemithorax may be opaque, and the heart may be pushed towards the normal side.

There are other patterns;

• Lamellar – A linear (lamellar) shadow paralleling the lateral aspect of the lung.

Encysted – Loculation within a fissure or elsewhere Sub-pulmonary – Pooling within the pleural space below the lung. This is a subpulmonary effusion and is a relatively common occurrence.

Pleural Effusion

A sub-pulmonary effusion is usually easier to detect on the left side, where the pool can cause the gastric air bubble to appear widely separate from the (apparent) superior margin of the diaphragm.

Note: The normal distance between the dome of the diaphragm and the air in the stomach does not normally exceed 7 mm in 98% of people aged 50 years and over

On the supine CXR

• When the patient is supine, pleural
• fluid layers out in the posterior part of the
• pleural space. This causes the hemithorax to appear whiter or paler grey than

the normal side.

In most instances the normal lung vessels will be seen through this shadowing. Approximately 200 ml of fluid needs to be present before an abnormal pale grey appearance is produced.

A “WHITE OUT” CAUSED BY A MASSIVE PLEURAL EFFUSION

A completely white hemithorax, often referred to as a “white out”, may be caused by a large volume (5–7 litres) of pleural fluid.

Assess pleural effusion in the following

chest radiographs