Sacral extradural arteriovenous fistula in a filum terminale lipoma with retained medullary cord: illustrative case.

backgroundSacral extradural arteriovenous fistula (AVF) associated with filum terminale (FT) is an extremely rare disease. Here, the authors report a progressive congestive myelopathy accompanied by tethered cord syndrome and lipoma. OBSERVATIONS: A 52-year-old woman who had a subcutaneous mass in the sacrococcygeal region since birth and developed urinary dysfunction 5 years earlier and gait disturbance 3 years earlier was referred for progressive paraplegia. She presented with myelopathy below the T11 level, and spinal MRI revealed edema with intramedullary hyperintensity changes, surrounding flow voids, and retain medullary cord with sacral lipoma. Spinal angiography revealed reflux from the left lateral sacral artery through the AVF within the lipoma to the vein of the FT within the dura mater. Preoperatively, the patient experienced worsening neurological symptoms, and endovascular embolization was followed by surgical curative treatment. Postoperatively, improvement in symptoms was observed. LESSONS: In sacral AVF associated with FT, knowledge of vascular anatomy and classification diagnosis significantly influence the treatment outcome. https://thejns.org/doi/10.3171/CASE26546.