(Fig. 5.18B). The rectus is covered posteriorly by the transversalis fascia, providing access to the muscle for the inferior epigastric vessels.
The transversalis fascia is a firm membranous sheet on the internal surface of the transversus abdominis muscle that extends beyond the muscle and forms a fascia lining the entire abdominopelvic cavity. Like the peritoneum, it is divided into a parietal and a visceral component. It is continuous from side to side across the linea alba and covers the posterior aspect of the rectus abdominis muscle below the arcuate line. Superiorly, it becomes the inferior fascia of the diaphragm. Inferiorly, it is attached to the iliac crest, covers the iliac fascia and the obturator internus fascia, and extends downward and medially to form the superior fascia of the pelvic diaphragm.
Characteristically, the transversalis fascia continues along blood vessels and other structures leaving and entering the abdominopelvic cavity and contributes to the formation of the visceral (endopelvic) pelvic fascia (32). The pelvic fascia invests the pelvic organs and attaches them to the pelvic sidewalls, thereby playing a critical role in pelvic support. In the inguinal region, the fascial relationships result in the development of the inguinal canal, through which the round ligament exits into the perineum. The fascia is separated from the peritoneum by a layer of preperitoneal fat. Areas of fascial weakness or congenital or posttraumatic and surgical injuries result in herniation of the underlying structures through a defective abdominal wall. The incisions least likely to result in damage to the integrity and innervation of the abdominal wall muscles include a midline incision through the linea alba and a transverse incision through the recti muscle fibers that respects the integrity of its innervation (33).
Nerves and Vessels The tissues of the abdominal wall are innervated by the continuation of the inferior intercostal nerves T4 to T11 and the subcostal nerve T12. The inferior part of the abdominal wall is supplied by the first lumbar nerve through the iliohypogastric and the ilioinguinal nerves. Abdominal wall surgical sites below the level of the anterior superior iliac spine have the potential for ilioinguinal or iliohypogastric injury (34). The primary blood supply to the anterior lateral abdominal wall includes the following: 1.
The inferior epigastric and deep circumﬂex iliac arteries, branches of the external iliac artery 2.
The superior epigastric artery, a terminal branch of the internal thoracic artery
The inferior epigastric artery runs superiorly in the transverse fascia to reach the arcuate line, where it enters the rectus sheath. It is vulnerable to damage by abdominal incisions in which the rectus muscle is completely or partially transected, during placement of lateral laparoscopic ports, or by excessive lateral traction on the rectus. The deep circumﬂex artery runs on the deep aspect of the anterior abdominal wall parallel to the inguinal ligament and along the iliac crest between the transverse abdominis muscle and the internal oblique muscle. The superior epigastric vessels enter the rectus sheath superiorly just below the seventh costal cartilage.
The venous system drains into the saphenous vein, and the lymphatics drain to the axillary chain above the umbilicus and to the inguinal nodes below it. The subcutaneous tissues drain to the lumbar chain.