On each side of the lower anterior abdominal wall, Hesselbach triangle is the region bounded laterally by the inferior epigastric vessels, inferiorly by the inguinal ligament, and medially by the lateral border of the rectus abdominis muscle. Hernias that protrude through the abdominal wall in Hesselbach triangle are termed direct inguinal hernias. In contrast, indirect inguinal hernias do so through the deep inguinal ring, which lies lateral to this triangle, and then may exit out the supericial inguinal ring.
he entire anterior abdominal wall is innervated by intercostal nerves (T 7-"i )ithe subcostal nerve (T'2)•' and the ilio hypogastric and the ilioinguinal nerves (L,). Of these, the
Intecostal n. Internaloblique m. External __.oblique m. Lateral Anterior ramus
FIGURE 2-2 Intercostal and subcostal nerves are the anterior rami of spinal nerves. In this figure, an intercostal nerve extends ventrally between the transversus abdominis and internal oblique muscles. During this path, the nerve gives rise to lateral and anterior cutaneous branches, which innervate the anterior abdominal wall. As shown by the inserted needle, the transversus abdominis plane (TAP) block takes advantage of this anatomy. (Modified with permission from Hawkins JL: Anesthesia for the pregnant woman. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al: Cunningham and Gilstraps's Operative Obstetrics, 3rd ed. New York, McGraw Hill Education, 201o7.) intercostal and subcostal nerves are anterior rami of the thoracic spinal nerves and run along the lateral and then anterior abdominal wall between the transversus abdominis and internal oblique muscles (Fig. 2-2). his space, termed the transversus abdominis plane, can be used for postcesarean analgesia blockade (Chap. 25, p. 500) (Fusco, 2015; Tawfik, 2017). Others report rectus sheath or ilioinguinaliliohypogastric nerve blocks to decrease postoperative pain (Mei, 2011; Wolfson, 2012).
Near the rectus abdominis lateral borders, anterior branches of the intercostal and subcostal nerves pierce the posterior sheath, rectus muscle, and then anterior sheath to reach the skin. hus, these nerve branches may be severed during a Pfannenstiel incision creation during the step in which the overlying anterior rectus sheath is separated from the rectus abdominis muscle.
In contrast, the iliohypogastric and ilioinguinal nerves originate from the anterior ramus of the first lumbar spinal nerve. They emerge lateral to the psoas muscle and travel retroperitoneally across the quadratus lumborum inferomedially toward the iliac crest. Near this crest, both nerves pierce the transversus abdominis muscle and course ventromedially. At a site 2 to 3 cm medial to the anterior superior iliac spine, the nerves then pierce the internal oblique muscle and course supericial to it toward the midline (Whiteside, 2003). The iliohypogastric nerve perforates the external oblique aponeurosis near the lateral rectus border to provide sensation to the skin over the suprapubic area (see Fig. 2-1). The ilioinguinal nerve in its course medially travels through the inguinal canal and exits through the supericial inguinal ring, which forms by splitting of external abdominal oblique aponeurosis fibers. This nerve supplies the skin of the mons pubis, upper labia majora, and medial upper thigh.