Chapter 18

### Anatomy of the Chest Wall & Pleura

The chest wall is an airtight, expandable, cone-shaped cage. Lung ventilation occurs by generation of negative pressure within the thorax due to simultaneous expansion of the rib cage and downward diaphragmatic excursion.

The ventral wall of the bony thorax is the shortest dimension. It extends from the suprasternal notch to the xiphoid—a distance of approximately 18 cm in the adult. It is formed by the vertically aligned manubrium, sternum, and xiphoid process. The first seven pairs of ribs articulate directly with the sternum, the next three pairs connect to the lower border of the preceding rib, and the last two terminate in the wall of the abdomen. The sides of the chest wall consist of the upper ten ribs, which slope obliquely downward from their posterior attachments. The posterior chest wall is formed by the 12 thoracic vertebrae, their transverse processes, and the 12 ribs (Figure 18–1). The upper ventral portion of the thoracic cage is covered by the clavicle and the subclavian vessels. Laterally, it is covered by the shoulder girdle and axillary nerves and vessels; dorsally, it is covered in part by the scapula.

###### Figure 18–1.

The thorax, showing rib cage, pleura, and lung fields.

The superior aperture of the thorax (also called either the thoracic inlet or the thoracic outlet) is a downwardly slanted 5- to 10-cm kidney-shaped opening bounded by the first costal cartilages and ribs laterally, the manubrium anteriorly, and the body of the first thoracic vertebra posteriorly. The inferior aperture of the thorax is bounded by the 12th vertebra and ribs posteriorly and the cartilages of the 7th to 10th ribs and the xiphisternal joint anteriorly. It is much wider than the superior aperture and is occupied by the diaphragm.

The blood supply and innervation of the chest wall are via the intercostal vessels and nerves (Figures 18–2 and 18–3), and the upper thorax also receives vessels and nerves from the cervical and axillary regions. The underside of the sternum’s blood supply derives from the internal thoracic artery branches, which anastomose with the intercostal vessels along the lateral aspect of the chest wall.

###### Figure 18–2.

Transverse section of thorax.

###### Figure 18–3.

Intercostal muscles, vessels, and nerves.

The parietal pleura is the innermost lining of the chest wall and is divided into four parts: the cervical pleura (cupula), costal pleura, mediastinal pleura, and diaphragmatic pleura. The visceral pleura is a mesodermal layer investing the lungs and is continuous with the parietal pleura, joining it at the hilum of the lung. The potential pleural space is a capillary ...

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