Generally, a thin film of serous fluid fills up the potential space which is the space between the parietal and visceral pleura. Enlargement of the space between Parietal and visceral pleura takes place in the regions of pleural reflection on to the diaphragm and mediastinum. Pleural Recesses is the name that is given to these enlarged regions of the pleural cavity. They play an important role in lung growth and deep inhalation. Hence, for lungs to enlarge during deep inhalation, pleural recesses act as reservation spaces of the pleural cavity. Following are the recesses of pleura:

  • Costodiaphragmatic recesses (left and right)
  • Costomediastinal recesses (left and right)

Along with the above recesses of pleura, there are 3 more small recesses, viz.

  • 1. Left and right retroesophageal recesses
    • All these are created by the reflection of mediastinal pleura supporting the esophagus. Every recess is believed to be inhabited by a part of the lung, and leads to the retrocardiac space viewed in the radiographs of the chest.
  • 2. Infracardiac recess
    • It’s a small recess of right pleural sac which occasionally goes below the inferior vena cava.

Costodiaphragmatic Recess

It’s found inferiorly between the costal and diaphragmatic pleurae. Vertically it measures about 5 cm and is located opposite the 8th-10th ribs along the midaxillary line. The costodiaphragmatic recesses are the most dependent parts of the pleural cavities, for this reason the fluid of pleural effusion first accumulate at these sites.

Costomediastinal Recess

It’s found anteriorly between the costal and mediastinal pleurae and is located between sternum and costal cartilages. The right costomediastinal recess is potentially inhabited by the anterior margin of the right lung even during quiet breathing. The left costomediastinal recess is large because of the presence of cardiacnotch in the left lung. Its location can be verified medically by percussion (tapping) of the chest wall. As 1 moves during tap from the area of underlying lung tissue to the area of left costomediastinal recess unoccupied by lung tissue, a change in tone, from resonant to muffled, is discovered. This is termed the area of superficial cardiac dullness.

Clinical Significance

Radiological Appearance Of Pleural Effusion

When a small volume of fluid accumulates in the costodiaphragmatic recess (pleural effusion) the costodiaphragmatic angle is obliterated (widening of the angle). It’s viewed as radiopaque darkness using a fluid line in X-ray chest. This could be the first indicator of pleural effusion. Consequently recesses of pleura are analyzed regularly in the chest radiographs.

The costodiaphragmatic recess can be entered via the 9th and 10th intercostal spaces without penetrating the lung in patient with silent breathing for the reason that it is located opposite 8th – 10th ribs.

Sites Of Expansion Of Pleura Beyond The Thoracic Cage

There are 5 sites, where pleura goes past the thoracic cage

These sites are as follows:

  • On each side in the root of the neck (as domes of pleura)
  • In the right xiphisternal angle
  • On each side in the costovertebral angle

The pleura can be punctured accidentally at these sites during surgical procedures.