Anatomy of the anterior abdominal wall and inguinal canal

Abstract 

The rectus abdominis occupies two-thirds of the anterior abdominal wall and is contained with the rectus sheath, made up of the aponeuroses of the lateral muscles – the external and the internal oblique and the transversus abdominis. The mid-line is marked by the linea alba and the lateral edge of rectus by the linea semilunaris. The rectus sheath is fused anteriorly to muscle but is free posteriorly, and contains the inferior and superior epigastric vessels. The space between rectus and the posterior sheath allows local anaesthetic to travel in this plane when performing a rectus block. The abdominal wall is innervated by the anterior primary rami of T7 to L1, T10 supplying the level of the umbilicus. The inguinal canal is the oblique passage taken through the lower abdominal wall by the testis and spermatic cord in the male and by the round ligament in the female. It also transmits the ilioinguinal nerve (L1). It is a point of potential weakness in the wall and is the site of direct and indirect ingunal hernias, which can be defined by their relationship to the inferior epigastric vessels. These lie medial to the neck of an indirect hernia, which passes through the internal ring of the canal, while a direct hernia, passing directly through the posterior wall of the canal, lies lateral to the vessels.

Keywords: indirect and direct inguinal hernias, inguinal canal, internal and external oblique muscles, rectus abdominis, rectus sheath, segmental nerve supply T7–L1, transversus abdominis