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

Abstract

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.