Anatomy of the pleura

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Introduction0:00–1:15

The pleura is a thin membrane that covers each of our lungs and surrounding pulmonary cavity, and it can be subdivided into two layers, the visceral pleura which intimately adheres to the lungs, and the parietal pleura which lines the rest of the pulmonary cavity.
Between these two pleural layers there’s the pleural cavity, which is normally filled with a thin film of fluid in order to lubricate the pleural surfaces and allow them to slide smoothly over each other during each breath.
Now, on the medial part of each lung, there’s the pulmonary hilum, where the root of the lung passes through. The root of the lungs is made of structures like the tracheobronchial tree, as well as arteries and veins.
At this level, the visceral and parietal pleura are continuous, making one continuous structure. To make this easier, you can imagine an underinflated balloon through which you press your fist into, the fist representing the root of the lung and the balloon representing the visceral and parietal pleura.
As you can see, the parietal and visceral pleura are one continuous layer, however they are reflected on different surfaces.

Visceral pleura 1:15–1:33

Okay, the visceral pleura covers the entire lung and adheres intimately to all its surfaces, including the ones between the fissures of each lung.
The visceral pleura is continuous with the parietal pleura at the hilum of the lung. The parietal pleura is thicker than the visceral one, lines the pulmonary cavities and adheres to the thoracic wall, mediastinum and diaphragm.

Parietal pleura1:33–3:46

The parietal pleura actually has four parts: costal, mediastinal, diaphragmatic and cervical pleura. The costal pleura covers the internal surface of the thoracic wall, from which it’s separated by the endothoracic fascia, a thin layer of loose connective tissue that comes in handy during surgical procedures, making it really easy to separate the lungs from the thoracic wall.
The mediastinal pleura covers the lateral aspects of the mediastinum, which is the space between the lungs and continues as cervical pleura superiorly in relation to the root of the neck.
It’s also continuous inferiorly with the diaphragmatic pleura and with the costal pleura anteriorly and posteriorly. At the hilum, the mediastinal pleura changes direction laterally onto the root of the lung to become one with the visceral pleura.
Superior to the hilum it is a continuous sheet passing between the sternum and vertebral column. The diaphragmatic pleura covers the superior surface of the diaphragm on each side of the mediastinum, minus where the diaphragm is fused with the pericardium and minus the diaphragm’s costal attachments to the xiphoid process anteriorly, to the 11th and 12th rib laterally.
Finally, the cervical pleura is basically a continuation of the costal and mediastinal pleura and covers the apex of the lungs, which is the part that extends through the superior thoracic aperture into the root of the neck.
Over the apex, the cervical pleura forms the pleural cupula, which domes over the apex that reaches its crest at about 2 to 3 centimeters superior to clavicle at the level of the neck’s first rib.
The cervical pleura is made stronger by a fibrous extension of the endothoracic fascia, called the suprapleural membrane.
This membrane attaches to the internal border of the first rib and the transverse process of C7 vertebra. So you see, the parietal pleura covers many different thoracic surfaces, and in doing so creates different lines called lines of pleural reflection.

Lines of pleural reflection3:46–4:22

There are 3 lines of pleural reflection on each side of the pulmonary cavities: sternal, costal and vertebral. By understanding these pleural lines of reflection, and how to find them with surface anatomy landmarks, we can locate the boundaries of the pleural cavity which is important during clinical interventions that need to access the pleural space between the parietal and visceral pleura.

Sternal lines of reflection 4:22–5:44

The sternal lines of reflection occur anteriorly at the point where the costal pleura is continuous with the mediastinal pleura.
They start superiorly from the cupulae and descend inferomedially, pass posterior to the sternoclavicular joints and meet at the anterior median line, at which point they descend together between the levels of costal cartilages 2 through 4 and then they split up again.
At this point, the sternal lines become asymmetrical, because the heart is positioned more to the left, so it leaves a bigger impression on the left lung.
So, the right sternal line continues to descend along the anterior medial line, posterior to the xiphoid process, at which point it turns laterally and becomes the costal line.
The left sternal pleural reflection descends on the anterior medial line only to the level of the 4th costal cartilage and at this point, it passes to the left margin of the sternum and continues to the 6th costal cartilage, creating a notch as it runs lateral to the bare area of the pericardium, located roughly at the left side of the midclavicular line and this is where the pericardium is in contact with the anterior thoracic wall.
At this point, the sternal line becomes the costal line. Now, the costal lines continue the sternal lines and they occur at the point where the costal pleura becomes continuous with the diaphragmatic pleura inferiorly.

Costal lines of reflection5:44–6:32

So the right costal line continues its journey from the anterior medial line. The left costal line continues its journey near the midclavicular line, because of the bare area of pericardium on the left.
Other than this, the right and left costal lines are symmetrical. They continue to descend posteriorly and then they make a turn around the 8th rib at the midclavicular lines and then another turn in the 10th rib at the midaxillary lines and then become continuous posteriorly with the vertebral lines at the necks of the 12th ribs.

Vertebral lines of reflection6:32–6:55

Finally, the vertebral lines of pleural reflection occur more gradually where the costal pleura becomes continuous with the mediastinal pleura posteriorly.
The vertebral lines are parallel to the vertebral column and run in the paravertebral planes from T1 through T12, afterwards they become continuous with the costal lines.

Pleural recesses6:55–7:41

Now, during expiration, the lungs don’t occupy the entire pulmonary cavities, so the diaphragmatic pleura is in contact with the lowest part of the costal pleura.
These pleural spaces are called the costodiaphragmatic recesses, which act as gutters lined in pleura, and they surround the upward convexity of the diaphragm in the thoracic wall.
There are also some smaller pleural recesses that are located posterior to the sternum where the costal pleura is in contact with the mediastinal pleura and these are called costomediastinal recesses.
The left recess is larger, because it’s less occupied, due to the cardiac notch in the left lung. Now just a quick pop quiz before the recap!!

Quiz7:41–7:57

Can you recall the four parts of the pleura, as well as the lines of pleural reflection? All right, as a quick recap, The lungs are located on each side of the thorax and are covered by the pleura.

Review7:57–8:47

The visceral pleura adheres intimately to the lung and the parietal pleura lines the pulmonary cavities. Between them, there’s a thin film of fluid located within the pleural cavity which allows for lubrication during respiration.
Now, the parietal pleura has 4 parts: costal, mediastinal, diaphragmatic and cervical pleura. When the parietal pleura changes direction, it forms three lines of pleural reflection: sternal, costal and vertebral.
The lungs don’t occupy the entire pulmonary cavity during expiration and as a consequence, the pleural spaces remaining form the costodiaphragmatic recesses and the