Teaching Case

Back pain

A lumbosacral MRI was requested for back pain. Turbo spin-echo T1-and T2-weighted images (slice thickness: 4mm) were acquired.

The normal thickness of the filum terminale is stated to be 2 mm or less. The diameter of a thickened and fatty filum terminale is usually above this size, and adipose tissue involving the filum usually extends over multiple spinal segments. It is usually an incidental finding, and is not a cause of back pain. MR imaging evidence of the lipomatous tissue associated with the filum is characterized by a intrathecal tissue distal to a normal conus medullaris that is hyperintense to the cord and to cerebrospinal fluid on T1-weighted images. In postmortem studies a 4%-6% incidence of an isolated fatty filum terminale has been reported, and it was suggested that the condition was a developmental anomaly consisting of fibrolipomatous involvement of the filum terminale. With respect to the embryogenesis of filum lipomas, it has been hypothesized that they probably result from an embryologic inclusion of the caudal neuropore. With respect to the differential diagnosis of these isolated filum lipomas intrathecal hemorrhage, and fat-containing dermoid or teratomatous tumors can be considered, however, these will usually show relevant symptoms. Also, the anatomical configuration of a thickened and fatty filum terminale, a multisegmental lesion involving the filum, enables the correct diagnosis.