Course of the thoracic nerves around the umbilicus within the posterior layer of the rectus sheath: a cadaver study

Rectus sheath block is used to anesthetize thoracic nerves around the umbilicus. However, the appropriate point for anesthetic injection during rectus sheath block has not been determined anatomically. Here, we examined the course of thoracic nerve T10 at the posterior layer of the rectus sheath and the anatomical relationship between the nerve and the rectus abdominis and transversus abdominis muscles in formalin-fixed adult cadavers. The cranio-caudal distance from a horizontal line running through the umbilicus to where the thoracic nerve T10 passes through the posterior layer of the rectus sheath was 33.8 ± 14.4 (mean ± standard deviation) mm, while that from the horizontal line running through the umbilicus to the position where the lateral edge of the rectus abdominis muscle and the medial border of the transversus abdominis muscle cross was 33.1 ± 17.1 mm. The position where the lateral edge of the rectus abdominis muscle and the medial border of the transversus abdominis muscle cross approximates the position where thoracic nerves T10 passes through the posterior layer of the rectus sheath. Our results identify effective landmarks to guide the performance of rectus sheath block.