Duplicated filum terminale in non-split cord malformations: An underrecognized cause for treatment failure in tethered cord syndrome.

Context: Anatomical variations of the filum terminale (FT) have been described in association with split cord malformations (SCM) but they appear to be a rare finding in its absence. We report the first case in literature of a duplicated FT in a patient presenting with tethered cord syndrome (TCS) without any radiological evidence of SCM.

Findings: A 47-year-old man presented with invalidating back pain radiating to both legs. Magnetic resonance imaging revealed an intradural dorsal lipoma in a low-lying conus. Intraoperatively two distinct fibrous bands were anatomically and electrophysiologically identified as the FT and both were sectioned. The diagnosis of FT was confirmed for both specimens by histology.

Conclusion: In absence of SCM, a duplicated FT has not been previously described as a cause of TCS. It may be a cause of treatment failure for TCS if unrecognized on preoperative imaging and during surgery if one filum remains intact. We highlight the importance of a meticulous cauda equina dissection supported by intraoperative nerve stimulation to identify this rare anomaly. We hypothesize that this entity may represent a variant of SCM involving the caudal neural tube but which requires further validation at an embryological level.