Spinal dural arteriovenous fistula masquerading as infiltrative intramedullary spinal cord tumor: illustrative case.

backgroundType 1 spinal dural arteriovenous fistulas (SDAVFs) are vascular malformations that present with nonspecific neurological manifestations and imaging characteristics that can closely resemble high-grade intramedullary spinal cord tumors (IMSCTs). OBSERVATIONS: The authors present the case of a 75-year-old male with 18 months of progressive thoracic myelopathy, who was referred for a spinal biopsy for a suspected IMSCT. The spine MRI study was notable for T2/short tau inversion recovery hyperintensity extending from T7 to L2 with no significant flow voids. MR angiography, digital subtraction angiography (DSA), and lumbar puncture studies were unremarkable. A corticosteroid trial did not delineate the underlying etiology, increasing diagnostic uncertainty between IMSCT and SDAVF. Therefore, a T11-12 laminectomy for a surgical exploration was indicated. Intraoperatively, an arterialized vein arising from the right T12 neural foramen was identified, confirmed with indocyanine green (ICG) angiography, and ligated. Postoperative clinical and radiographic improvement confirmed the diagnosis of SDAVF. LESSONS: This case illustrates how SDAVF can masquerade as infiltrative IMSCT, emphasizing the importance of maintaining a high index of clinical suspicion for arteriovenous shunting during the workup of suspected IMSCT. A repeat DSA study should be considered when the initial DSA is negative, and in the setting of surgical exploration, the early use of intraoperative ICG angiography can be valuable for identifying pathology successfully. https://thejns.org/doi/10.3171/CASE25787.