Conus medullaris

The conus medullaris is the tapered, cone-shaped lower end of the spinal cord. It typically ends at the level of the L1 vertebra in adults. Superiorly, it is continuous with the more proximal segments of the spinal cord, while inferiorly, it transitions into the filum terminale, a slender, fibrous band of pia mater.

Within the conus medullaris, the spinal cord contains the S2 to S5 spinal segments and the coccygeal segment, which contribute to the:

• Motor innervation of the lower extremities.

• Sensory innervation of the perineum and genital regions.

• Autonomic control, particularly over the bowel, bladder, and sexual function through sacral parasympathetic outputs.

Clinical Correlations:

The conus medullaris has immense clinical significance. A notable condition associated with a lesion in the conus medullaris includes the Conus medullaris syndrome which entails a constellation of symptoms, such as, sudden onset of lower back pain, symmetric bilateral motor weakness in the lower limbs, perianal sensory loss, bowel and bladder dysfunction (usually early onset), and erectile dysfunction.

Differentiation from Cauda Equina Syndrome:

While both syndromes affect the lower spinal regions, conus medullaris syndrome has symmetric motor deficits and mixed upper and lower motor neuron signs (like hyperreflexia). In contrast, cauda equina syndrome features asymmetric weakness, lower motor neuron signs (hyporeflexia), and typically later onset of bowel/bladder dysfunction.