ANATOMY OF ILIOINGUINAL AND ILIOHYPOGASTRIC NERVES IN RELATION TO TROCAR PLACEMENT AND LOW TRANSVERSE INCISIONS

J. Whiteside, MD, M. Barber, MD MHS, M. Walters, MD, T. Falcone, MD.

   Objective: To map the course of the ilioinguinal and iliohypogastric nerves within the anterior abdominal wall in order to identify a “safe zone” for abdominal incisions and trocar placement that would avoid operative injury.

   Materials and Methods: Gross dissection was performed on 9 female fresh frozen cadavers. The course of iliohypogastric and ilioinguinal nerves was mapped from their lateral emergence on the anterior abdominal wall to their termination in the midline. Measurements were made in reference to fixed bony landmarks including the xyphoid process (X), pubic symphysis (PS), and anterior superior iliac spine (ASIS). Bivariate fit ellipses of the 95% confidence intervals of the course of each nerve were calculated in order to determine “danger zones” for potential nerve injury. Morphometric results were then compared to the locations of recommended laparoscopic trocar sites in the lower abdomen and locations of standard lower abdominal transverse skin incisions.

   Results: The anterior abdominal wall course of 12 iliohypogastric and 13 ilioingual nerves were identified and mapped. There was considerable variability of the course of both nerves within the 9 cadavers. On average the proximal end of the ilioinguinal nerve entered the abdominal wall 3.3 cm (SD ± 1.5 cm, range 1.1 to 5.3 cm) medial and 3.6 cm (SD ± 1.6 cm, range –0.5 to 5.9 cm ) inferior to the ASIS, then followed a linear course to terminate 2.8 cm (SD ± 0.9 cm, range 1.6 to 4.4 cm) lateral to the midline and 1.9 cm (SD ± 0.9 cm, range 0.9 to 3.8 cm ) superior to PS. The iliohypogastric nerve entered the abdominal wall on average 2.2 cm (SD ± 1.9 cm, range –1.6 to 5.0 cm ) medial and 0.8 cm (SD ± 2.9 cm, range –5.4 to 5.5 cm ) inferior to the ASIS, then followed a linear course to terminate 3.8 cm (SD ± 2.8 cm, range 1.0 to 10.6 cm ) lateral to the midline and 5.2 cm (SD ± 2.7 cm, range 2.1 to 10.9 cm ) superior to PS. A safe zone for lower abdominal laparoscopic troc! ar placement exists 2 cm above a line drawn transversely between the right and left ASIS. Trocars placed within 1 cm of the midline will also avoid ilioinguinal and iliohypgastric injury.

   Conclusions: Due to the variability of the course of the ilioinguinal and iliohypogastric nerves, laparoscopic trocar placement in the right and left lower quadrants below the ASIS has the potential for ilioinguinal or iliohypogastric injury. Similarly, all standard transverse lower abdominal incisions have the potential of injuring the ilioinguinal and iliohypogastric nerves.

   Key Words: Ilioinguinal nerve, Iliohypogastric nerve, Entrapment, Surgical incision, Complications