Ilioinguinal and Iliohypogastric Nerve Blocks

Anatomical Overview¹

Ilioinguinal and Iliohypogastric Nerve Course

• Both nerves arise from the anterior ramus of L1. The iliohypogastric nerve occasionally receives nerve fibers from T12 as well.
• The ilioinguinal nerve is smaller and courses inferior and medial to the iliohypogastric nerve.
• The ilioinguinal and iliohypogastric nerves commonly branch at the lateral border of the psoas major muscle (Figure 1).
• Both nerves travel anterior to the quadratus lumborum and pierce the transversus abdominis near the iliac crest.
• Both nerves proceed within the fascial plane between the transversus abdominis and internal oblique muscles. This location is critical for effective nerve blockade.

• The ilioinguinal nerve provides sensory innervation to the upper medial thigh and genitalia (scrotum or labia majora).
• The iliohypogastric nerve provides sensory innervation to the suprapubic region and posterolateral gluteal region through its anterior and lateral cutaneous branches.
• The ilioinguinal and iliohypogastric nerves both provide motor innervation to the internal oblique and transversus abdominis muscles. This contributes to the structural and functional stability of the lower anterior abdominal wall.

Nerve Block^1,3

Overview

• The ilioinguinal and iliohypogastric nerves are commonly blocked together due to their vicinity and being in the same fascial plane.
• The genital branches of the ilioinguinal and the iliohypogastric nerves may be either distinct or fused to constitute a common trunk. In 60% of cases, the distal portions of the iliohypogastric and the ilioinguinal nerve are united to a single genital branch.¹
• The most common approach to the ilioinguinal and iliohypogastric nerve is either by landmark technique or under US guidance. The failure rates are as high as 45–72% in the landmark technique.³

Ilioinguinal Nerve Block

• Objective: Provide local anesthesia to the inguinal region, upper medial thigh, and genital structures.
• Common Indications: Inguinal hernia repair, pediatric groin surgeries, orchiectomy, and varicocele surgery.
• Probe placement: The patient should be lying supine, and the probe should be placed posterior and superior to the anterior superior iliac spine (ASIS). Position the probe perpendicular to the path of the ilioinguinal nerve, which typically runs parallel to the inguinal ligament. The lateral edge of the probe should rest on the iliac crest as seen with probe A (Figure 2).

• Anatomy visualized: Identify the external oblique, internal oblique, and transversus abdominis muscles.
  • The ilioinguinal nerve lies between the transversus abdominis and internal oblique muscles. The ilioinguinal nerve will be closest to the iliac crest, within 1.5cm.
  • In some cases, the ilioinguinal and iliohypogastric nerves can be as close as 1cm apart.⁴

• Color Doppler US should be used to visualize the deep circumflex iliac artery, which lies within the same fascial plane and is close to the ilioinguinal nerve, to avoid bleeding complications.

• Complications: Puncture of the deep circumflex iliac artery can lead to local hematoma. Advancing the needle too deeply can lead to a bowel perforation.

Iliohypogastric Nerve

• Probe placement: Similar to ilioinguinal nerve block placement. The slight difference is that the anterior and lateral cutaneous branches of the iliohypogastric nerve may pierce the internal and external oblique above the ASIS. It’s recommended to perform the nerve block more superior to the ASIS, before the nerve branches.
• Objective: Effectively provide regional anesthesia to the suprapubic and lower lateral abdominal wall region.
• Common Indications: Pfannenstiel incisions, appendectomy, cesarean sections, renal transplant, and lower abdominal scar pain.
• Complications: Mistaking the iliohypogastric nerve for the subcostal nerve, which can lead to aberrant distribution of anesthesia.

Risk Reduction

US Guidance

• An US-guided block allows for accurate needle placement that can reduce the risk of adverse outcomes.
• Failure rates are as high as 45–72% in the landmark technique.³
• US-guided technique offers a strong clinical effectiveness, with studies indicating a success rate exceeding 95%.⁷
• Proper training and anatomical awareness are key to a successful nerve block