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Ilioinguinal nerve

The ilioinguinal nerve is a mixed sensory and minor motor branch of the lumbar plexus. It arises from the anterior ramus of the L1 spinal nerve and provides sensation to the upper medial thigh, anterior scrotum in males, and mons pubis/labia majora in females. It is clinically significant because of its superficial course in the groin and frequent involvement in surgical injury, hernia repair, and neuropathic pain.

Synonyms

  • Nervus ilioinguinalis

  • L1 anterior branch (ilioinguinal portion)

Origin, Course, and Branches

  • Origin: Arises from the anterior ramus of the L1 spinal nerve (sometimes with contributions from T12)

  • Course:

    • Emerges from the lateral border of the psoas major muscle

    • Passes obliquely across the quadratus lumborum and iliacus muscles

    • Pierces the transversus abdominis near the iliac crest

    • Runs between the transversus abdominis and internal oblique before piercing the internal oblique

    • Travels through the inguinal canal and emerges from the superficial inguinal ring

  • Branches:

    • Provides sensory fibers to the upper medial thigh, root of penis and anterior scrotum in males, mons pubis and labia majora in females

    • Minor motor contributions to abdominal wall muscles (transversus abdominis and internal oblique)

Relations

  • Superior: Iliohypogastric nerve (runs parallel but slightly higher)

  • Inferior: Inguinal ligament and spermatic cord/round ligament

  • Medial: Genitofemoral nerve

  • Lateral: Iliacus muscle and iliac crest

Function

  • Sensory:

    • Upper medial thigh

    • Anterior scrotum and root of penis in males

    • Mons pubis and labia majora in females

  • Motor (minor):

    • Contributes to innervation of transversus abdominis and internal oblique muscles

Clinical Significance

  • Commonly injured during inguinal hernia repair, C-section, and appendectomy

  • Entrapment or injury leads to ilioinguinal neuralgia (burning or stabbing groin pain radiating to scrotum/labia)

  • Important landmark in groin surgeries and anesthesia nerve blocks

  • Can be targeted for ilioinguinal nerve block for analgesia in hernia and lower abdominal procedures

MRI Appearance

T1-weighted images:

  • Nerve shows low-to-intermediate signal intensity against bright fat background

T2-weighted images:

  • Nerve demonstrates intermediate to mildly hyperintense signal compared to muscle

  • Pathological nerve (neuropathy, inflammation) may appear brighter

STIR (Short Tau Inversion Recovery):

  • Normal nerve appears dark to low signal

  • Injured or inflamed nerve becomes bright hyperintense

T1 Fat-Sat Post-Contrast:

  • Normal nerve shows minimal enhancement

  • Pathology (neuritis, tumor, entrapment) shows focal or diffuse enhancement

3D T2 SPACE / CISS:

  • Nerve appears intermediate to mildly hyperintense relative to muscle

  • Surrounded by very bright fat or CSF, enhancing contrast

  • Allows fine tracing of the nerve through retroperitoneum and inguinal canal

CT Appearance

Non-Contrast CT:

  • Nerve not directly visible, but inferred as a thin soft tissue structure within fat planes of the groin

  • Fat planes along iliacus and inguinal canal outline its expected course

Post-Contrast CT:

  • Nerve itself does not enhance significantly

  • Pathologic thickening, infiltration, or adjacent masses may enhance, outlining the nerve path indirectly

MRI image

Ilioinguinal nerve MRI CORONAL IMAGE 2

MRI image

Ilioinguinal nerve MRI CORONAL IMAGE

MRI IMAGE

Ilioinguinal nerve mri axial