Anatomy - Anterolateral thoracotomy

Beneath the skin of the thorax, there are several fasciae and muscle layers from outside to inside: The pectoral fascia is a fascia that lies externally on the M. pectoralis major, while the clavipectoral fascia envelops the M. pectoralis minor. The bony thorax itself also has its own fasciae: The thoracic fascia covers the periosteum of the ribs externally as well as the muscles of the intercostal spaces, while the endothoracic fascia represents its internal counterpart on the periosteum of the ribs as well as the internal or innermost intercostal muscles. It is covered by the parietal pleura (pleural membrane) towards the interpleural space. All these fasciae, including the intercostal muscles (see below), are penetrated during thoracotomy.

Blood vessels (intercostal vessels) and nerves (intercostal nerves) of the thoracic wall run in a ring-like manner along the inner side of the thorax, corresponding to the original segments of the organism. Via the blood vessels, the dorsally located vessels aorta and V. azygos/hemiazygos are segmentally connected with the respective ventral A. and V. thoracica interna. The latter arises from the A. subclavia, runs together with its eponymous accompanying veins bilaterally parallel to the sternum immediately outside the fascia endothoracica in a caudal direction, and then divides at the level of the diaphragm (Larrey's cleft) into the A. epigastrica superior (which anastomoses with the A. epigastrica inferior from the A. iliaca externa) and an artery to the diaphragm (A. musculophrenica). Along this path, on the inner side of the thorax, it gives rise primarily to the anterior parts of the intercostal arteries as well as branches to the mediastinum.

The intercostal arteries thus have an anterior inflow from the A. thoracica interna and are supplied dorsally either directly from the aorta (3rd – 11th branch) or the A. subclavia (via the costocervical trunk). Below the 12th rib, the A. subcostalis runs as a counterpart. Regarding the overall course of the intercostal arteries, it is important that the respective dorsal portions of the arteries run along the lower edge of the overlying rib (together with intercostal vein and nerve) up to the level of the anterior axillary line and then typically divide into an upper and a lower branch (at the lower or upper edge of the adjacent ribs). Typical accumulations of lymph nodes are found in the area of the chest wall parasternal, axillary, as well as just above and below the clavicle.