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Medial cluneal nerves

The medial cluneal nerves are small purely sensory cutaneous nerves that arise from the dorsal rami of the sacral spinal nerves (S1–S3). They pierce the posterior sacroiliac ligaments and gluteal fascia to supply the skin of the medial buttock. Though relatively small, they are clinically important because their entrapment can cause cluneal neuralgia, a recognized cause of chronic buttock or low back pain.

Synonyms

  • Medial buttock nerves

  • Sacral cutaneous nerves (medial group)

  • Sacral dorsal rami branches

Origin, Course, and Branches

  • Origin: Dorsal rami of S1, S2, and S3 spinal nerves

  • Course:

    • Emerge from the posterior sacral foramina

    • Pass laterally, piercing the posterior sacroiliac ligaments and gluteal fascia

    • Distribute toward the medial aspect of the buttock

  • Branches: Terminal cutaneous fibers supplying the skin of the medial gluteal region

Relations

  • Anteriorly: Sacrum and sacroiliac ligaments

  • Posteriorly: Skin and subcutaneous tissue of medial buttock

  • Superiorly: Related to superior cluneal nerves (from L1–L3 dorsal rami)

  • Inferiorly: Continuous with inferior cluneal nerves (from posterior femoral cutaneous nerve)

  • Laterally: Overlap zone with superior cluneal nerve distribution

Function

  • Provide sensory innervation to the skin of the medial buttock

  • No motor function

  • Contribute to cutaneous sensation in posterior pelvic and gluteal regions

Clinical Significance

  • Entrapment or injury can cause medial cluneal neuralgia, presenting as localized buttock pain radiating to the sacrum or posterior thigh

  • May be compressed by scar tissue, sacroiliac dysfunction, or trauma

  • Can mimic sciatica or sacroiliac joint pain

  • Recognized target for nerve blocks, radiofrequency ablation, and neuromodulation in chronic buttock pain management

MRI Appearance

T1-weighted images:

  • Nerves appear as thin low-to-intermediate signal linear structures within bright fat of the posterior pelvis and gluteal region

T2-weighted images:

  • Nerves demonstrate intermediate to mildly hyperintense signal relative to muscle

  • Pathology (edema, neuritis, entrapment) appears brighter

STIR (Short Tau Inversion Recovery):

  • Normal nerves show low signal

  • Inflamed or edematous nerves demonstrate bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal nerves enhance minimally

  • Pathologic nerves may enhance focally or diffusely in neuritis or tumor involvement

3D T2 SPACE / CISS:

  • Medial cluneal nerves appear as intermediate to mildly hyperintense linear structures compared to muscle

  • Surrounded by bright CSF or fat, making them easier to trace

  • Helpful for identifying entrapment sites at the posterior sacroiliac ligaments

CT Appearance

Non-Contrast CT:

  • Nerves are not directly visible

  • Their course can be inferred by fat planes adjacent to posterior sacrum and sacroiliac region

  • Chronic entrapment may show adjacent fat stranding

Post-Contrast CT:

  • Nerves themselves do not enhance

  • Pathology (e.g., inflammation, tumor infiltration) may appear as enhancing soft tissue along expected course

  • Calcified or scarred sacroiliac ligaments may be seen compressing nerves

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