Topics

Topic

design image
Coccygeal nerve

The coccygeal nerve is the 31st spinal nerve and the most caudal nerve of the spinal column. It arises from the conus medullaris of the spinal cord, emerging through the sacral hiatus. It contributes to the coccygeal plexus, a small network formed by the ventral ramus of Co1 and a branch from the ventral ramus of S4 or S5. Despite being the smallest spinal nerve, it plays an important role in sensory innervation of the perianal region.

Synonyms

  • Co1 spinal nerve

  • Coccygeal spinal nerve

  • Lowest spinal nerve

Origin, Course, and Branches

  • Origin:

    • Arises from the spinal cord at the coccygeal level (Co1)

  • Course:

    • Exits through the sacral hiatus along with the fifth sacral nerve roots

    • Contributes to the coccygeal plexus with fibers from S4, S5, and Co1

    • Runs forward over the coccygeus muscle

  • Branches:

    • Gives rise to the anococcygeal nerves, which pierce the sacrotuberous ligament and innervate the skin in the coccygeal region

Relations

  • Anteriorly: Coccygeus muscle and pelvic floor structures

  • Posteriorly: Sacrum and coccyx

  • Laterally: Sacral nerve roots and sacral plexus components

  • Inferiorly: Skin and fascia of the coccygeal region

Function

  • Provides sensory innervation to the skin over the coccyx and anococcygeal region

  • Contributes to motor fibers to part of the coccygeus muscle and external anal sphincter (via coccygeal plexus)

  • Plays a role in pelvic floor stabilization and continence mechanisms

Clinical Significance

  • Injury may occur during falls on the coccyx, childbirth, or sacral surgery

  • Associated with coccydynia (coccygeal pain), sometimes requiring nerve block or resection

  • Important in anococcygeal nerve blocks for chronic coccygeal pain

  • May be visualized or compressed in cases of tumors, trauma, or congenital anomalies of the sacrococcygeal region

MRI Appearance

T1-weighted images:

  • Appears as a small, thin low-signal nerve root at the sacral hiatus and coccygeal region

  • Surrounded by bright epidural and subcutaneous fat that helps delineation

T2-weighted images:

  • Nerve root demonstrates intermediate signal intensity

  • Surrounded by bright cerebrospinal fluid in proximal region and soft tissue planes distally

STIR (Short Tau Inversion Recovery):

  • Normal coccygeal nerve appears as a low-signal structure

  • Pathology such as inflammation, neuritis, or nerve entrapment shows bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal nerve shows minimal or no enhancement

  • Pathology such as neuritis, tumor infiltration, or postoperative scarring may enhance focally or diffusely

CT Appearance

Non-Contrast CT:

  • Nerve is not directly visualized, but its location is inferred by the sacral hiatus and coccygeal canal

  • Bony anomalies, fractures, or spicules compressing the nerve can be detected

Post-Contrast CT:

  • Nerve itself enhances poorly

  • Pathological changes such as tumors, infection, or inflammatory soft tissue masses around the sacrococcygeal region may show enhancement

MRI image

Coccygeal nerve MRI axial anatomy image-img-00000-00000

MRI image

Coccygeal nerve MRI axial anatomy image-img-00000-00000_00001