Anterolateral abdominal wall

The anterolateral abdominal wall refers to the lower part of the anterior trunk. It comprises partly of bony but mainly of skeletal muscles.

The underlying bony framework consists of the costal arch, superiorly. The arch comprises of xiphoid process of sternum and costal cartilages of 7th -10th ribs. Inferiorly, the expanded parts of pelvic bones provide a bony base for attachment of skeletal muscles.

The major part of anterolateral abdominal wall is composed of muscles. Laterally, we can identify three flat sheet-like muscles. From superficial to deep, these include the external oblique, internal oblique and transversus abdominis muscles. All three muscles can be differentiated by their distinct orientation of muscle fibers. However, one thing which they share in common is that as they approach anteriorly, towards the midline, each muscle expands to form a fibrous connective tissue sheath called the ‘aponeurosis’. Their aponeuroses envelop an anteriorly situated, abdominal wall muscle called the rectus abdominis. The rectus abdominis is vertically oriented, and attached to pubic symphysis below and the lower ribs above. Its anterior and posterior coverings–formed by the aponeuroses of lateral abdominal wall muscles–are called anterior and posterior rectus sheaths. Close to the midline, and medial to the rectus abdominis muscle, the aponeuroses of all three lateral abdominal wall muscles fuse with each other, forming a tough fibrous structure called the linea alba.

Inferiorly, in the groin or inguinal region, the anterolateral abdominal wall muscles form the walls of the inguinal canal.

The anterolateral abdominal wall muscles are innervated by the lower six thoracic spinal nerves. The flex and bend the trunk. The muscles function to compress and push the abdominal contents upwards, thus pushing the diaphragm superiorly and assisting in expiration, coughing and vomiting. The increased intra-abdominal pressure helps in activities such as micturition, defecation and also in child birth.

Similar to other parts of the body, the anterolateral abdominal wall–from outside to inside–is covered over by skin, superficial and deep fascial layers.

Below umbilicus, the superficial fascia splits up into a superficial fatty layer (a.k.a. Camper’s fascia) and a deep membranous layer (a.k.a. Scarpa’s fascia). The former descends further to envelope the penis and scrotum as the dartos fascia, while the latter descends further into the perineum and attaches to the ischiopubic rami and posterior margin of perineal membrane as the Colles’ fascia (a.k.a. superficial perineal fascia).

Deep or underneath the anterolateral abdominal wall muscles, one can find various fascial layers, including the transversalis fasica, extraperitoneal fascia and parietal peritoneum.