Fatty filum terminale (FFT) as a secondary tethering element in children with closed spinal dysraphism

The purpose of this study was to assess the prevalence of FFT as an additional tethering element in children operated for closed spinal dysraphism, where FFT was not the primary tethering pathology.

This is a retrospective study of 195 children (< 18 years of age) who underwent surgery for closed spinal dysraphism and did not have FFT as the primary diagnosis. All patients were operated during the period 2005-2017 by a single surgeon. The commonest diagnosis was a lipomyelomeningocele (LMMC, n = 81, 41.5%), followed by split cord malformations (SCM, types I and II, n = 61, 31.3%), dermal sinus (n = 28, 14.4%), and dermoid cyst (n = 10, 5.1%). Factors such as age and sex, presenting symptoms, intraoperative findings, and radiological presence of a FFT on a magnetic resonance imaging (MRI) were documented, and the relationship between the primary diagnoses and presence of FFT was analyzed.

FFT as a secondary finding was seen in 63 patients (32.3%). The mean age of the cohort was 54 months (4.5 years) and the sex distribution was relatively even (51.8% girls). The commonest symptom at presentation was a swelling in the back, followed by lower limb weakness. The mean duration of symptoms was nearly 30 months. FFT was seen on the MRI and confirmed intraoperatively in 55 patients (28.2%). There were 8 patients (4.1%) where a FFT was seen intraoperatively, but was not diagnosed on the preoperative MRI. In 16 patients, FFT was seen > 2 segments away from the primary tethering pathology, 8 of which mandated a second skin incision for sectioning of the FFT. Secondary FFT was most commonly associated with a SCM (types I and II combined) and was seen in 42.6% of those patients. It was least commonly associated with intradural dermoid cysts.

The presence of a secondary FFT should be considered and actively sought on preoperative thin-slice T1W axial MR images in the sacral region in all patients with spinal dysraphism. Even if a FFT is not seen on preoperative MR images, the filum should be explored and sectioned if it is in the vicinity of the primary surgical field, especially in patients with SCM.