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Conus Medullaris

conus medullaris

The conus medullaris is the tapered terminal end of the spinal cord, normally ending at the L1-L2 vertebral level in adults (L3 in neonates). Below the conus, only the cauda equina (nerve roots) occupies the thecal sac in CSF. The conus contains the sacral spinal cord segments S1-S5 responsible for bladder and bowel control, sexual function, and perineal sensation.

Region: Lower Back

Clinical Relevance

Clinical Notes

Conus medullaris injury from fractures at the thoracolumbar junction (T12-L2) produces a mixed picture: upper motor neurone features from cord involvement combined with lower motor neurone features from root involvement. The classic conus syndrome includes areflexic bladder and bowel (from direct S2-S4 conus involvement), saddle anaesthesia, and sexual dysfunction, with variable lower limb motor involvement. MRI localises the conus accurately before surgical decompression.

Pathology

Common Injuries & Conditions

Conus Medullaris Syndrome

Injury to the conus at T12-L2 produces areflexic neurogenic bladder and bowel from sacral centre involvement combined with variable lower motor neurone weakness of the legs, saddle anaesthesia, and sexual dysfunction; the mixed upper and lower motor neurone picture distinguishes conus from pure cauda equina or pure spinal cord injury.