Pleura is a serous membrane that covers the lungs.

It consists of two layers:

Visceral pleura - covers the lungs from the outside, also spreading between the lobes of the lungs;
Parietal pleura - extends along the inner wall of the thorax.

The parietal pleura has four parts:

Costal pleura - covers ribs, intercostal spaces and intercostal muscles;
Diaphragmatic pleura - covers the diaphragm from above, except its central part;
Mediastinal pleura - covers the lateral aspects of the mediastinum, extending from the sternum to the spine in a sagittal plane and demarcating the mediastinum;
Cervical pleura - lines the extension of the pleural cavity into the neck.

There is a fluid-filled space between the visceral and parietal layers of the pleura on each side, which is called the pleural cavity. It is filled with a small volume of serous fluid.

This fluid lubricates both layers so that they can slide over each other. It also “sticks” parietal and visceral layers together, producing a surface tension. This ensures that when the thorax expands, the lungs also expand to fill with air.

Areas between the parts of the parietal pleura are not completely filled by the lungs, and this creates recesses.

Each pleural cavity presents with two major recesses - the costodiaphragmatic recess and the costomediastinal recess.

Costodiaphragmatic recess is located between the border of the diaphragm and the inner surface of the thorax wall at the site where the costal pleura becomes the diaphragmatic pleura. It happens along the inferior border of the lung.

Costomediastinal recess is located at the posterior surface of the sternum, where the costal pleura passes into the mediastinal pleura. It happens along the anterior border of the lung.

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Pleura