General structure and parts
The pleura is a thin serous membrane consisting of two layers. The visceral (pulmonary) pleura is tightly fused with the lung parenchyma and extends into its interlobar fissures. The parietal pleura lines the thoracic cavity from the inside and separates the lungs from the mediastinal organs.
The parietal layer is subdivided into three parts depending on what it is adjacent to:
- Costal pleura;
- Diaphragmatic pleura;
- Mediastinal pleura.
The sites where one part of the parietal pleura transitions into another are called transition folds, or recesses. They form the boundaries of the entire pleural cavity.
Boundaries of the parietal pleura
The anterior boundaries of the pleural sacs (the lines where the costal pleura transitions into the mediastinal pleura) are asymmetrical, as the left pleural fold is displaced by the heart.
Anterior boundary:
- Right: descends medially from the sternoclavicular articulation, crosses the midline at the level of the 2nd rib cartilage, and runs vertically downward to the attachment of the 6th rib cartilage to the sternum.
- Left: runs similarly down to the 4th rib cartilage, then forms the cardiac notch, deviating laterally (crossing the 4th intercostal space, the 5th rib cartilage, the 5th intercostal space) and passes into the inferior boundary at the midpoint of the 6th rib cartilage.
At the level of the 2nd–4th rib cartilages, the right and left pleural sacs come into contact. Above and below this area, the superior and inferior interpleural spaces are formed.
Inferior boundary (identical on both sides):
- Along the midclavicular line — 7th rib;
- Along the midaxillary line — 10th rib;
- Along the scapular line — 11th rib;
- Along the paravertebral line — 12th rib.
The posterior boundary runs along the costovertebral joints.
Cervical pleura
The apex of the pleural sac, or cervical pleura (cupula), projects into the neck area above the clavicle. Its height depends on the body type and potential pathologies in the apex of the lung.
Projection of the cupula:
- Anteriorly — 2–3 cm above the clavicle.
- Posteriorly — corresponds to the level of the spinous process of the 7th cervical vertebra.
Syntopy (adjacent structures):
- Posteriorly: head and neck of the 1st rib, longus colli muscles, stellate ganglion (inferior cervical sympathetic ganglion).
- Laterally and anteriorly: scalene muscles and structures of the brachial plexus.
- Medially: on the right, adjacent to the brachiocephalic trunk; on the left, to the left common carotid and subclavian arteries.
Pleural sinuses
Pleural recesses (recessus pleurales) are reserve spaces at the sites where different parts of the parietal pleura transition into one another. Normally, their walls are in contact, and the lungs enter them only during inspiration (fluid accumulates there in pathology).
The costodiaphragmatic recess (recessus costodiaphragmaticus) is the largest. It extends in a semicircle from the 6th rib cartilage to the spine.
- At the level of the 6th rib, its depth is about 2 cm.
- The maximum depth reaches 8 cm at the level of the 7th–10th ribs (along the midaxillary line).
- Feature: even during the deepest inspiration, the lung does not completely fill this recess.
- Clinical significance: in the posterior regions, the recess extends below the 12th rib, creating a risk of accidental opening during surgical approaches to the kidney.
The remaining recesses (costomediastinal, anterior and posterior mediastinal-diaphragmatic) are significantly smaller and are usually fully expanded by the lungs during inspiration.
Briefly: answers to topical questions
What organs and structures are contained within the superior and inferior interpleural spaces?
The thymus and pericardium are located within the interpleural spaces.
- The thymus (Thymus) is contained within the superior interpleural space, where it is adjacent to the retrosternal fascia.
- The pericardium is located in the inferior interpleural space, directly adjacent to the chest wall, and forms the zone of "absolute cardiac dullness".
Which arteries supply blood to the parietal and visceral pleura?
The blood supply to the visceral pleura is provided by the bronchial vessel system.
- Bronchial arteries (Arteriae bronchiales) supply oxygen to the visceral pleura, as well as the bronchial tree and lung parenchyma.
Information on the sources of arterial blood supply to the parietal pleura is lacking, but it is known that venous drainage from it enters the systemic circulation via the veins of the thoracic wall.
Which nerves innervate the parietal pleura?
The parietal pleura receives afferent fibers as part of the intercostal nerves and the phrenic nerve (n. phrenicus).
In which intercostal space and along which line is thoracentesis classically performed for fluid accumulation?
Classic thoracentesis is performed in the lower regions of the thoracic cage.
- The optimal point is the 5th–6th intercostal space along the midaxillary line (linea axillaris media). In this area, the muscle layer of the chest wall is the thinnest, making the procedure the least traumatic.
- Insertion rule: the puncture is performed strictly along the upper margin of the underlying rib. This is necessary to avoid damaging the intercostal nerve and vessels, which run along the lower margin of the overlying rib.
The lower boundary of the pleura is easy to remember using odd/even rib numbers on the main lines: midclavicular — 7, axillary — 10 (exception, take the middle one), scapular — 11, paravertebral — 12.
Class and exam questions
Why are the anterior pleural borders asymmetric?
The left anterior boundary deviates laterally starting from the level of the 4th rib due to the position of the heart, which displaces the pleura, forming the cardiac notch.
Which pleural recess is the deepest?
Costodiaphragmatic recess. Its maximum depth is about 8 cm along the midaxillary line.
Where is the cupula of the pleura projected anteriorly and posteriorly?
Anteriorly, the cupula projects 2–3 cm above the clavicle, and posteriorly it is projected at the level of the spinous process of the 7th cervical vertebra.
What else to study on this topic
- Mechanism of serous fluid formation and drainage in the pleural cavity
- Ligamentous apparatus of the cupula of the pleura and interpleural spaces
- Topography of interlobar fissures and projection of lung lobes onto the chest wall
- Anatomical rationale for sites for pleural puncture
- Syntopy of the mediastinal pleura with mediastinal organs
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