 The last well formed disk space is referred to as L5-S1. The conus medullaris ends at mid L2 level which is within normal limits. There is a 14 AP x 32 CC x 9 ML mm nonenhancing intradural extramedullary cystic mass extending from the tip of the conus medullaris inferiorly to the mid L5 level. It has a broad base along the posterior dural surface and follows CSF signal on all sequences. This mass causes mass effect with displacement of the cauda equina nerve roots ventrally which drape around the contour of the mass. There is no dysraphism. There is linear nonenhancing 2-mm thick intrinsic T1 shortening structure along the posterior midline aspect of the thecal sac inferior to the lower aspect of the cystic mass likely representing fatty filum. Lack of prone imaging limits evaluation.There are no vertebral body anomalies in the lumbar spine. There is no pathologic enhancement elsewhere. The vertebral body heights are intact. The osseous marrow signal is within normal limits. The intervertebral disks show normal height and signal intensity.
1.Large dorsal intradural extramedullary nonenhancing CSF signal cyst described above with displacement of the cauda equina nerve roots which are draped around the contour of the cyst. Differential considerations include arachnoid cyst versus epidermoid. Given absence of associated vertebral body anomalies in the lumbar spine at the levels of the cyst, neuroenteric cyst is felt to be unlikely.2.Conus medullaris terminates at L2 which is within normal limits. Likely incidental fatty filum, although sometimes it can be associated with a tethered cord. Prone imaging was not performed as this was an unexpected finding. Please correlate clinically.