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Coccygeal plexus

The coccygeal plexus is a small network of nerves formed by the ventral rami of the lower sacral and coccygeal spinal nerves. It is the smallest of all nerve plexuses and contributes to innervation of the skin and tissue around the coccyx and anus. Despite its size, it is clinically important in pelvic surgery, pain syndromes, and imaging interpretation of the sacrococcygeal region.

Synonyms

  • Plexus coccygeus

  • Coccygeal nerve plexus

  • Anococcygeal plexus

Location and Roots

  • Formed by the ventral ramus of S4, the ventral ramus of S5, and the coccygeal nerve (Co1)

  • Lies on the pelvic surface of the coccygeus muscle and adjacent part of the sacrum and coccyx

  • Located posterior to the pelvic viscera and anterior to the sacrococcygeal ligament

Branches

  • Anococcygeal nerves: Small branches that pierce the sacrotuberous ligament and coccygeus muscle to reach the skin overlying the coccyx

  • Communicating branches to the sacral sympathetic trunk and pelvic splanchnic nerves

Relations

  • Anteriorly: Pelvic viscera (rectum) and pelvic fascia

  • Posteriorly: Sacrum and coccyx

  • Laterally: Coccygeus and levator ani muscles

  • Inferiorly: Skin and subcutaneous tissue of the coccygeal region

Function

  • Provides sensory innervation to the skin of the coccyx and anal region via anococcygeal nerves

  • Contributes to proprioceptive and nociceptive signals from the sacrococcygeal joint

  • Plays a minor role in motor innervation to parts of the coccygeus muscle

  • Supports pelvic floor sensory feedback mechanisms

Clinical Significance

  • Involved in coccydynia (tailbone pain), often due to trauma, degeneration, or childbirth injury

  • Target for coccygeal nerve block or ganglion impar block in chronic pelvic and perineal pain

  • May be affected by pelvic tumors, fractures, or infections in the sacrococcygeal region

  • Important landmark in surgical procedures of the pelvic floor and perineum

MRI Appearance

T1-weighted images:

  • Plexus itself is seen as low-to-intermediate signal thin nerve bundles

  • Surrounded by bright fat which provides contrast

T2-weighted images:

  • Nerve bundles show low signal intensity

  • Pathological changes such as edema or inflammation may cause focal bright signal around nerves

STIR (Short Tau Inversion Recovery):

  • Nerves normally remain dark

  • Inflammatory or edematous tissue surrounding the plexus shows bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal nerves show minimal enhancement

  • Pathology (inflammation, tumor infiltration) may cause irregular or focal enhancement

CT Appearance

Non-Contrast CT:

  • Nerves of the plexus are not individually visible; seen indirectly as soft tissue density around the sacrococcygeal junction

  • Bony landmarks (sacrum, coccyx) are clearly visualized

  • Masses or calcification in the region may compress or distort plexus

Post-Contrast CT:

  • Normal nerves show no significant enhancement

  • Pathologic processes (abscess, tumor, inflammatory mass) may enhance and alter fat planes surrounding the plexus

MRI image

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

MRI image

Coccygeal plexus MRI coronal anatomy image-img-00000-00000