Refining the course of the thoracolumbar nerves: A new understanding of the innervation of the anterior abdominal wall

Previous descriptions of the thoracolumbar spinal nerves innervating the anterior abdominal wall have been inconsistent. With modern surgical and anesthetic techniques that involve or may damage these nerves, an improved understanding of the precise course and variability of this anatomy has become increasingly important. The course of the nerves of the anterior abdominal is described based on a thorough cadaveric study and review of the literature. Twenty human cadaveric hemi-abdominal walls were dissected to map the course of the nerves of the anterior abdominal wall. Dissection included a comprehensive tracing of nerves and their branches from their origins in five specimens. The branching pattern and course of all nerves identified were described. All thoracolumbar nerves that innervate the anterior abdominal wall were found to travel as multiple mixed segmental nerves, which branch and communicate widely within the transversus abdominis plane (TAP). This communication may occur at multiple locations, including large branch communications anterolaterally (intercostal plexus), and in plexuses that run with the deep circumflex iliac artery (DCIA) (TAP plexus) and the deep inferior epigastric artery (DIEA) (rectus sheath plexus). Rectus abdominis muscle is innervated by segments T6-L1, with a constant branch from L1. The umbilicus is always innervated by a branch of T10. As such, identification or damage to individual nerves in the TAP or within rectus sheath is unlikely to involve single segmental nerves. An understanding of this anatomy may contribute to explaining clinical outcomes and preventing complications, following TAP blocks for anesthesia and DIEA perforator flaps for breast reconstruction.