Pleural cavity

The pleural cavity is a potential space (in healthy patients) composed by the layers of visceral pleura and parietal pleura that are continuous with one another around and below the root of the lung, forming a closed invaginated sac.

When the lung collapses or when air or fluid collects between the two layers the cavity becomes apparent.

The right and left pleural sacs are entirely separate from one another; between them are all the thoracic viscera except the lungs, and they only touch each other for a short distance in front; opposite the second and third pieces of the sternum the interval between the two sacs is termed the mediastinum.

The reflections of the pleura form different recesses in the pleural cavity.