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Conus medullaris

The conus medullaris is the tapered, terminal end of the spinal cord, located at the level of L1–L2 vertebrae in adults (slightly lower in children). It represents the distal continuation of the spinal cord before transitioning into the cauda equina and the filum terminale, which anchors the cord to the coccyx.

It is cylindrical in shape, narrowing as it approaches its termination, and contains the lower lumbar, sacral, and coccygeal spinal cord segments. The conus lies within the lumbar spinal canal, surrounded by cerebrospinal fluid (CSF) in the thecal sac, and is stabilized by the filum terminale internum and externum.

The exact level of the conus is clinically significant: a low-lying conus may suggest tethered cord syndrome, while mass lesions or trauma at this level can cause profound motor and sensory deficits.

Synonyms

  • Terminal spinal cord

  • Spinal cord cone

  • Medullary cone

Function

  • Marks the termination of the spinal cord proper

  • Gives rise to lumbar, sacral, and coccygeal spinal cord segments

  • Transitions into the cauda equina (nerve roots) and filum terminale

  • Coordinates motor and sensory innervation of lower limbs, bladder, bowel, and pelvic organs

Nerve Supply

  • Contains spinal cord segments from L1 to coccygeal (Co1)

  • Gives rise to lumbar, sacral, and coccygeal nerve roots forming the cauda equina

  • Integrates motor and sensory pathways for pelvic floor, bladder, bowel, and perineum

Arterial Supply

  • Supplied by the anterior spinal artery and paired posterior spinal arteries

  • Reinforced by segmental arteries, especially the artery of Adamkiewicz (major anterior radiculomedullary artery, usually from T9–L2)

Venous Drainage

  • Venous outflow via the anterior and posterior spinal veins into the internal vertebral venous plexus

MRI Appearance

T1-weighted images:

  • Conus appears as an intermediate signal structure tapering to the filum terminale

  • Surrounded by hyperintense CSF, aiding contrast

T2-weighted images:

  • Conus medullaris is intermediate signal, clearly outlined by hyperintense CSF

  • Pathology (edema, demyelination, tumor) appears as hyperintensity

STIR:

  • Suppresses fat signal, enhancing visualization of edema, inflammation, or demyelination

  • Sensitive for cord injury and myelitis

T1 Fat-Saturated (Pre-contrast):

  • Conus appears as intermediate signal against suppressed fat

  • Useful for detecting cord contour and adjacent fat planes

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normally does not enhance

  • Abnormal enhancement indicates tumor, demyelination, inflammation, or vascular malformation

MRI Non-Contrast 3D Imaging:

  • Provides multiplanar 3D view of the cord termination, cauda equina, and filum terminale

  • Crucial in evaluating tethered cord, syringomyelia, or congenital anomalies

CT Appearance

CT Pre-Contrast:

  • Cord itself poorly visualized; appears as a soft-tissue density within the thecal sac

  • Limited role except in trauma (detecting fractures affecting conus)

CT Post-Contrast (CT Myelography):

  • Contrast in CSF outlines the conus medullaris and cauda equina

  • Helpful in cases where MRI is contraindicated

  • Detects blockage of CSF pathways, tethered cord, or compression

MRI image

Conus medullaris MRI sagittal anatomy image -img-00000-00000

MRI image

Conus medullaris MRIcoronal anatomy image -img-00000-00000

CT image

Conus medullaris ct sagittal image