Surgical Outcome of Tethered Cord Syndrome Following Duplicate Filum Terminale Externum Resection in a Patient With Normal Conus Medullaris and Fatty Filum: A Case Report

We describe the case of a 38-year-old woman who limped due to a forced antalgic posture involving plantar flexion of the left foot. She exhibited hypoesthesia on the posterior aspect of the left lower limb. The lumbar MRI showed the conus medullaris in a normal position and a fatty filum (FF) extending from L3 to L5, with a maximum diameter of 5.5 mm at L3. A transhiatal approach was performed to section the filum terminale externum (FTE) to achieve spinal cord untethering, and a duplicated FTE was found. The symptoms disappeared immediately but recurred several months later. A second surgical approach was undertaken through a partial sacrectomy via S1-S2 laminectomy, as the section of the FTE did not reveal any other anatomical variants apart from the duplicated FTE, which was sectioned near the inferior part of the dural sac. The symptoms temporarily resolved, but after a few months, they reappeared, presenting differently from the initial symptoms, which involved the proximal parts of the lower limbs. The section of the intradural FF was then performed, and the symptoms disappeared at five years of follow-up. In this case, the potential limitations of the therapeutic capabilities of minimally invasive surgery for section FTE by transhiatal approach, related to the anatomical variation of the duplicate FTE, were eliminated by sectioning the duplicated FTE at the point where the dural sac emerges and by excluding the presence of a duplicate filum terminale internum during the section of the FF. The presence of the FF and its significant thickness should be recognised as a limitation to the effectiveness of the FTE section in treating tethered cord syndrome.