Tethered cord syndrome caused by duplicated filum terminale in an adult with split cord malformation.

Background Tethered cord syndrome (TCS) is a clinical diagnosis of progressive neurologic aggravation of the lower spinal cord due to a traction on the conus medullaris. Untethering surgery is effective for most TCS; however, when anatomic variations of spinal cord and filum terminale (FT) exist, regular untethering may lead to a failed outcome. Case Description The authors present the case of a 45-year-old patient with TCS caused by duplicated FT with split cord malformation (SCM). Lumbosacral magnetic resonance imaging revealed a type II SCM with a significant low-lying conus medullaris. Laminectomy was performed. Neurophysiologic monitoring was used for nerve root identification and 2 thickened fila, which failed to respond on stimulation, were found during the surgery. Both fila were sectioned, and the diagnosis was finally confirmed by pathologic examination. Postoperatively, the patient's symptoms disappeared immediately and no neurologic sequela was found after surgery. Conclusions This is the first documented adult of duplicated FT with preoperative radiologic evidence and reported in association with SCM as a cause of TCS. When SCM exists, a careful observation for duplicated FT is warranted on preoperative magnetic resonance imaging and during surgery. Complete transection of the double FT under intraoperative neurophysiologic monitoring is the best treatment for this anomaly.