From superficial to deep, the external oblique, internal oblique, and transversus abdominis muscles anterolaterally and the rectus abdominis muscles medially form the abdominal wall. Deep to these muscles, the transversalis fascia separates the abdominal visceral contents from the muscles that form the abdominal wall. The nerves that innervate the abdominal wall musculature and supply sensory innervation to its overlying skin and peritoneum are derived from the ventral rami of the intercostal nerves from the 6th to 12th thoracic spinal nerves (T6 to T12) and the 1st lumbar spinal root (L1). The anterior and lateral cutaneous branches of the ventral rami of the intercostal nerves travel in the plane between the internal oblique muscle and the transversus abdominis muscle (known as the TA plane - TAP). There is a thin fascial sheet between the internal oblique muscle and transversus abdominis muscle in which the nerves lay between the fascia and the transversus abdominis muscle. The cutaneous branches of the T6 to T12 nerves branch and communicate with adjacent nerves within the TA plane, forming an extensive network that results in three plexuses: the intercostal plexus anterolaterally, the TAP plexus running with the deep circumflex iliac artery, and the rectus sheath plexus running with the deep inferior epigastric artery. The macroanatomy and sonoanatomy (static and dynamic) of these muscles and nerves are discussed in this chapter.
Keywords: Acute pain medicine, Anterior rectus sheath, Arcuate line, Cutaneous branches of ventral rami, External oblique muscle, Iliohypgastric nerve, Ilioinguinal nerve, Intercostal nerves, Internal oblique muscle, Lumbar spinal roots, Peritoneum, Posterior rectus sheath, Regional anesthesia, TA plane, TAP, Transversalis fascia, Transversus abdominis muscle Rectus abdominis muscle, Ventral rami of the intercostal nerves.