Intrathecal endoscopy to enhance the diagnosis of tethered cord syndrome

Tethered cord syndrome (TCS) is being diagnosed in an increasing number of adults and late teens. Before referral to neurosurgeons, however, the majority of patients in this group suffers back and leg pain for a long period without a definitive diagnosis. The diagnostic difficulty derives from 2 factors: the signs and symptoms are subtle and easily overlooked, and the combination of an elongated cord and a thickened filum is lacking in 65% of patients. When a patient presents with signs and symptoms typical for TCS but demonstrates no elongated cord or thickened filum on MR imaging, one must search for a more reliable finding to establish a diagnosis of TCS. Based on the authors' earlier surgical experiences, posterior displacement of the terminal filum is consistently found at surgery in all patients with TCS. In previous publications they interpreted this finding as the lower cord and filum traveling along the concave side of the lumbosacral spinal canal to minimize cord tension. In the present prospective study, the authors attempt to confirm posterior displacement of the filum terminale by using intrathecal endoscopy prior to wide exposure of the spinal cord and filum. Further, the stretch test was applied to the terminal filum to evaluate its elasticity.

Sixty-eight patients with signs and symptoms as well as MR imaging studies indicative of TCS underwent endoscopic examination of the filum and cauda equina. After lumbar or sacral laminectomy, a flexible endoscope was inserted through a small dural and arachnoid incision into the subarachnoid space. The filum and cauda equina fibers were identified. Once the dura mater and arachnoid were opened widely, a stretch test was done to confirm filum inelasticity. In 3 patients, percutaneous endoscopy was also performed before open surgery to determine its applicability as compared with the open method.

On inserting the endoscope into the intrathecal space, the filum was immediately identified medioposterior to the cauda equina fibers in all 68 patients. The stretch test revealed a lack of filum elasticity in all patients. Preoperative percutaneous endoscopy was equally effective in identifying the position of the filum.

Currently, endoscopic identification of the posteriorly displaced filum, which was confirmed at open surgery, is the essential diagnostic study for TCS or the tethered spinal cord. Furthermore, the stretch test of the filum proves its inelasticity, and filum sectioning leads to ascension and relaxation of the caudal spinal cord. These results can be linked to the impaired oxidative metabolism of the lumbosacral cord under excessive tension and to the metabolic and neurological improvements seen after filum sectioning.