Pleural Cavity

Pleura is a greek word that literally means ‘side of the body.’ It was used in medieval latin and eventually took on a new and more specific anatomical meaning in the late middle form of the english language. Today it describes the two thin membranes known as the visceral and parietal pleurae that surround the lungs.

The pleural cavity is the potential space between these two membranes that is created when the serous pleura covers the lung and folds back upon itself, leaving a small pouch or air pocket. In this article, the boundaries of the pleural cavity, the cavity itself, the pleural reflections and recesses as well as the potential pathological presentations within this region will be discussed.

Parietal pleura - lateral-left view

Boundaries

The boundaries or border limits of the pleural cavity are marked out using the straight lines used to strategically place and measure the internal organs. All of these lines are either horizontal or vertical and originate from a specific anatomical landmark.

• At the level of the right sixth rib and the fourth left rib at the anterior midline
• At the level of the twelfth rib at the scapular line
• At the level of the eighth rib at the midclavicular line
• At the level of the tenth rib at the midaxillary line

Pleural cavity - lateral-right view

It should be noted that during clinical practice, if a patient has quiet respiration then at the inferior border of the lungs the previously mentioned borders, save the first in the list is the same value minus two ribs. So for example at the level of the (10th - 2) 8th rib at the midaxillary line.

The Cavity

There are two pleural cavities, one for each lung. The first layer is the visceral layer and that lines the lung tissue and its fissures. The second is the parietal layer and that lines the the wall of the cavity by sticking to the inner aspect of the thorax.

There are four regions of the pleura that are named according to the anatomical structure that is adjacent to it. The costal pleura lines the cavity along the ribs, the mediastinal pleura lines the cavity along the mediastinum, the diaphragmatic pleura lines the cavity along the diaphragm and finally the cervical pleura or cupula lines the dome that forms at the apex of the lung.

Costal part of parietal pleura - ventral view

Pleural Reflections and Recesses

A pleural reflection is a line or curvature that occurs when a fold is made so that the pleura can change direction. Posteriorly there is a vertebral reflection, inferiorly a costal reflection and anteriorly a sternal reflection.

A pleural recess is a potential smaller space or cavity created when the pleural touch one another in times of quiet respiration. These recesses are most likely to occur as a costomediastinal space or a costodiaphragmatic space.

Costodiaphragmatic recess - ventral view