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The conus medullaris is the terminal end of the spinal cord.
After the cord terminates, the nerve roots descend within the spinal canal as individual rootlets, collectively termed the cauda equina. The conus medullaris most commonly terminates at the L1/2 intervertebral disc level in children and adults 1-3.
Extending from the conus is a delicate strand of fibrous tissue called the filum terminale that acts to give longitudinal support to the cord.
The termination of the conus medullaris has been reported from mid-T11 to mid-L3 vertebral body levels. The average termination varies from study to study 1-3, but a level at or above the L2/3 intervertebral disc level can be considered normal. A level at L3 vertebral body is equivocal and can be a normal variant or the result of a tethered cord 1.
On fetal MRI, the vertebral bodies can be difficult to count accurately. However, the kidneys may be used as a reference, and a normal conus should not terminate below the lower margin of normally positioned kidneys.