The conus medullaris (Latin for "medullary cone") or conus terminalis is the tapered, lower end of the spinal cord. It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower.[1][2] The upper end of the conus medullaris is usually not well defined, however, its corresponding spinal cord segments are usually S1–S5.
After the spinal cord tapers out, the spinal nerves continue to branch out diagonally, forming the cauda equina.[1]
The pia mater that surrounds the spinal cord, however, projects directly downward, forming a slender filament called the filum terminale, which connects the conus medullaris to the back of the coccyx. The filum terminale provides a connection between the conus medullaris and the coccyx which stabilizes the entire spinal cord.[3]
Conus medullaris syndrome is a collection of signs and symptoms associated with injury to the conus medullaris.[4] It typically causes back pain and bowel and bladder dysfunction, spastic or flaccid weakness depending on the level of the lesion, and bilateral sensory loss. Comparatively, cauda equina syndrome may cause radicular pain, bowel/bladder dysfunction, patchy sensory loss or saddle anesthesia and lower extremity weakness at the level of the lumbar and sacral roots.
Isolated infarcts of the conus medullaris are rare, but should be considered in patients with acute cauda equina syndrome, especially in females. According to a 2021 paper by You-Jiang Tan, et al., those with demonstrated causes or with vascular risk factors are less likely to walk without assistance.[6]
↑Tubbs RS, Elton S, Bartolucci AA, Grabb P, Oakes WJ (November 2000). "The position of the conus medullaris in children with a Chiari I malformation". Pediatr Neurosurg. 33 (5): 249–251. doi:10.1159/000055963. PMID11155061. S2CID7270480.
