Object: Spinal cord tethering due to a thickened filum terminale is a well-described entity that can be treated surgically. Postoperative MR imaging of the lumbar spine is performed for unrelated issues or for the development of new symptoms suggestive of cord retethering. A lack of radiological criteria for successful detethering makes interpretation of postoperative MR images challenging. The delineation of postoperative radiological characteristics of a sectioned filum terminale is therefore valuable to clinicians managing these often complex cases.
Methods: The clinical data for 16 patients who underwent sectioning of a fatty and thickened filum between 2001 and 2010 and in whom pre- and postoperative MR imaging studies were available were analyzed. Medical records were interrogated for preoperative neurological examination, operative details, and postoperative follow-up. The MR images were examined by both a neurosurgeon and a neuroradiologist to assess postoperative radiological characteristics.
Results: The patients' age at time of surgery ranged from 0.3 to 19.8 years (mean 7.5 years). Postoperative MR imaging was performed between 0.03 and 7.36 years after the procedure (mean 2.5 years). Indications for postoperative imaging included new neurological symptoms (11 of 16 patients), routine interval imaging (3 of 16), and possible development of pseudomeningocele (2 of 16). Filum discontinuity was confirmed in 79% of cases postoperatively. Filum remnants appeared thicker after surgery in most cases (80%), a phenomenon most often appreciated in the cephalad end of the sectioned filum. Postoperatively, the conus was elevated in 5 cases (31%) and was found to be more ventrally located in 7 cases (44%).
Conclusions: Discontinuity, along with thickening of the upper and lower remnants of a sectioned filum, may constitute important radiological features of a detethered filum. Radiological signs of conus relaxation, signified by elevation or a more ventral position, although reassuring, were less reliably observed postoperatively. Because it may be difficult to know if the goals of surgery were met on purely clinical grounds in this patient population, knowledge of the postoperative characteristics of a sectioned filum may aid the practicing neurosurgeon in the management of these complex cases.