Magnetic resonance imaging based anatomy of the conus medullaris: variations of location and morphology.

Background: In adults, the conus medullaris( CM) tip usually terminates at the mid aspect of the L1 vertebra. However, variations exist. Beside the location, differences in the CM's shape are believed to be closely related to neurological conditions.

Methods: This was a prospective observational study. We enrolled consecutive patients with non-traumatic complaints of lower back pain and/or sciatica. Two observers independently performed the measurements and determined the location and shape of the CM. The length of each vertebral body was divided into 3 equal lengths.. The shape of the CM was determined according to Moon et al. into three types; A,B and C.

Results: A total of 1000 patients met the inclusion criteria. The age was 42.72 ± 13.14 years and 556 were male (55.6%). Overall, the most frequent location of the CM was the lower third of the L1 vertebral body, with some variations according to the age category. The level of agreement according to location was good (κ = 0.787). Overall, the most frequent shape of the CM was type B, followed by type C and type A. The level of agreement was very good. No correlations could be found between the shape and location of the CM.

Conclusion: The majority of participants had the CM at the caudal level of L1. We did not observe any highly positioned CM above T12. There is good reliability of interobserver agreement of the current methods for description of the location and shape of CM.