Intramedullary Spinal Arteriovenous Malformations-Definition of Two Distinct Subtypes

INTRODUCTION: Intramedullary spinal arteriovenous malformations (SpiAVM) are complex lesions. Due to their rarity, reports of their management and outcomes are limited. METHODS: Our neurovascular database was reviewed SpiAVMs between January 1986 and December 2021. Demographic, clinical, radiographic, and outcome data were obtained. Eccentric SpiAVMs were defined as those with a significant portion presenting through the pia mater into the subarachnoid space, with large vessels coursing outside the parenchyma. Concentric SpiAVMs were defined as those embedded within the spinal cord parenchyma, not presenting to pia mater, and well circumscribed. RESULTS: Fifty-nine patients (mean [SD] age, 34 [15] years; female sex, 34) were identified. Patients exhibited myelopathy (88%), including pain (51%), paresis (88%), sensory deficits (46%), and bowel and bladder dysfunction (46%). Twenty-seven patients (46%) presented with hemorrhage. Forty-nine percent of lesions were located in the cervical spine and 51% in the thoracic spine. Thirty-five lesions (59%) were previously embolized. Twenty-eight patients (51%) were classified as eccentric and 27 (49%) as concentric SpiAVMs. Postoperative outcomes were similar with no significant differences (improved, 8/18 [44%] vs. 9/17 [53%]; unchanged, 8/18 [44%] vs. 7/17 [41%]; worse, 2/18 [11%] vs. 1/17 [6%]). Retreatment rates were not significantly different between both subtypes (eccentric, 9/28 [32%]; concentric, 6/27 [22%]). Eccentric and concentric SpiAVMs were associated with similar rates of complete resection (eccentric, 14/26 [54%], concentric, 18/26 [69%]). Of 55 classifiable lesions, 4 (7%) were determined to have a mixed phenotype, harboring characteristics of eccentric and concentric SpiAVMs. CONCLUSIONS: Intramedullary AVMs may cause significant symptoms. The eccentric and concentric subtypes have different angioarchitecture and outcomes. While complete resection is usually the preferred surgical objective, eccentric SpiAVMs are amenable to the pial resection that may achieve angiographic obliteration without complete resection.