2 – Anatomy of the rectus sheath

The rectus sheath is made by the anterior aponeuroses of the lateral abdominal muscles (external and internal obliques and the transverse abdominis) that split into an anterior and a posterior layer that encloses the rectus abdominis muscle on each side; the two layers fuse on the medial side of the rectus muscle and attach to the linea alba

The anterior layer of the rectus sheath extends from the xiphoid process to the pubic symphysis

The posterior layer only extends 3-5 cm below the umbilicus to the socalled arcuate line and it is separated from the peritoneum by the transversalis fascia

The 9th, 10th, and 11th intercostal nerves and the epigastric blood vessels are sandwiched between the rectus abdominis muscle fascia and the posterior layer of the rectus sheath

Blockade of these nerves with a rectus sheath block produces periumbilical anaesthesia