Ilioinguinal/Iliohypogastric Nerve Block

ANATOMY

Both the iliohypogastric (IH) and ilioinguinal (II) nerves arise from L1 and emerge from the upper part of the lateral border of the psoas major muscle. The ilioinguinal nerve is a smaller nerve and courses caudad to the iliohypogastric nerve.

Both nerves cross obliquely anterior to the quadratus lumborum and iliacus muscles and perforate the transverse abdominis muscle near the anterior part of the iliac crest. In the anterior abdominal trunk, the nerves travel between the transverse abdominis and the internal oblique muscles.

Blockade of the II and IH nerves is indicated for analgesia following inguinal hernia repair because the nerves provide sensory innervation to the skin of the lower abdominal wall in addition to the upper hip and upper thigh. Because the lateral cutaneous branch of the IH nerve may pierce the internal and external oblique muscles immediately above the iliac crest, it is worthwhile to block the nerves as proximal as possible (i.e., posterior to the anterior superior iliac spine) before the nerve branches.

SCANNING TECHNIQUE

• Position the patient supine.
• Expose the lower abdomen, the iliac crest and the groin area. Mark the anterior superior iliac spine (ASIS).
• After skin and transducer preparation, place a linear 10-12 MHz transducer oblique (as shown in figure) along a line joining the ASIS and the umbilicus immediately superior and medial to the ASIS.

Optimize machine imaging capability; select appropriate depth of field (usually within 1-3 cm), focus range and gain.

NERVE LOCALIZATION

• Perform a systematic anatomical survey from the iliac crest to the lower abdomen.
• The II and IH nerves are expected to lie within the fascial plane between the transverse abdominis and internal oblique muscles above the ASIS.
• It is important to note that the two nerves may pierce the internal oblique muscle layer at the ASIS level and travel more superficially between the internal and external oblique muscles.
• Identify the three muscular layers of the abdominal wall: the external oblique (most external), the internal oblique and transverse abdominis muscles. The external oblique muscle may be seen only as a thin layer of aponeurosis.
• Identify the peritoneal cavity and bowel movement deep to the transverse abdominis muscle layer.
• The two nerves are often hypoechoic in appearance.
• Trace the course of the nerve proximally to the region above ASIS and then distally towards the inguinal region if possible .
• It is common to visualize small vessels adjacent to the II and IH nerves within the same plane. Use Color Doppler to confirm vascular identity.

Arrows = ilioinguinal/iliohypogastric nerves   ASIS = anterior superior iliac spine   EOM = external oblique muscle   IOM = internal oblique muscle   TAM = transverse abdominis muscle

IN PLANE NEEDLE INSERTION APPROACH

• Ultrasound guided II/IH nerve block is considered an INTERMEDIATE skill level block. It is challenging is to image the small nerves and insert the needle in the fascial plane.
• Insert a 5-8 cm 22 G needle parallel to and inline with the transducer and the ultrasound beam. It is generally easy to visualize the needle shaft and tip during needle advancement because this is a superficial block.

A needle (arrows) inserted in plane with its tip above the II/IH nerves (arrowheads) is seen on ultrasound.   IOM = internal oblique muscle   TAM = transverse abdominis muscle

• It may be challenging to clearly visualize the needle tip and accurately place the needle in the fascial plane between the internal oblique and transverse abdominis muscle layers. Because this plane is a narrow space, it is worthwhile to inject small amount of fluid (1-2 mL of saline or local anesthetic) to “hydro dissect” the appropriate plane.
• If the needle is placed inaccurately inside one of the muscle layers, intramuscular fluid injection is seen during “hydro dissection.”

LOCAL ANESTHETIC INJECTION

• Needle placement in the correct plane is indicated by fluid expansion in a space bounded by the hyperechoic fascial sheath of the internal oblique and transverse abdominis muscle layers.
• A total of 10-20 ml of local anesthetic is injected into this plane.
• If only small vessels are visualized in the fascial plane and not the II/IH nerves, deposit the same volume of local anesthetic around the vessels in this plane.

Figure A shows hypoechoic nerves within the plane between the internal oblique muscle (IOM) and the transverse abdominis muscle (TAM).

Figure B shows the II/IH nerves completely surrounded by local anesthetic (LA).   IOM = internal oblique muscle   TAM = transverse abdominis muscle

IMAGE GALLERY

1. An Example of Improper Local Anesthetic Spread

Pre-injection   Arrowheads = II/IH nerves in between   EOM = external oblique muscle   IOM = internal oblique muscle   TAM = transverse abdominis muscle

Injection # 1   Local anesthetic (LA) is injected partially within the internal oblique muscle (IOM) and partially in the plane between the internal oblique muscle and the transverse abdominis muscle (TAM).   EOM = external oblique muscle

An ill defined collection of local anesthetic (LA) is seen around the nerves. The accuracy of injection is questionable resulting in a partial block.

Injection # 2   EOM = external oblique muscle   IOM = internal oblique muscle   TAM = transverse abdominis muscle

2. Locating A Branch of the Deep Circumflex Iliac Artery

Several hypoechoic structures (arrowheads) may be located within the plane between the internal oblique muscle (IOM) and the transverse abdominis muscle (TAM). It is important to use Color Doppler or Color Power Doppler to identify the branch of the deep circumflex iliac artery (red dot) and not to inadvertently target the artery.   EOM = external oblique muscle

EOM = external oblique muscle   IOM = internal oblique muscle   Red dot = deep circumflex iliac artery   TAM = transverse abdominis muscle

SELECTED REFERENCES

• Eichenberger U, Greher M, Kirchmair L, Curatolo M, Moriggl B. Ultrasound-guided blocks of the ilioinguinal and iliohypogastric nerve: accuracy of a selective new technique confirmed by anatomical dissection. Br J Anaesth 2006;97:238-243.
• Gofeld M, Christakis M. Sonographically guided ilioinguinal nerve block. J Ultrasound Med 2006;25: 1571-1575.
• Willschke H, Bosenberg A, Marhofer P, Johnston S, Kettner S, Eichenberger U, Wanzel O, Kapral S. Ultrasonographic-guided ilioinguinal/iliohypogastric nerve block in pediatric anesthesia: what is the optimal volume? Anesth Analg 2006;102: 1680-1684.
• Willschke H, Marhofer P, Bosenberg A, Johnston S, Wanzel O, Cox S G, Sitzwohl C, Kapral S. Ultrasonography for ilioinguinal/Iliohypo-gastric nerve blocks in children. Br J Anaesth 2005;95:226-230.