Type I spinal arteriovenous fistulae exception: a case for reclassification.

OBJECTIVE: Type I spinal arteriovenous lesions represent dorsal dural arteriovenous fistulae with no spinal artery involvement. We report an exception to this and propose dividing Type I lesions into dorsal and ventral categories.
METHODS: A 51-year-old patient presented with a partial Brown-Sequard syndrome. An angiogram revealed a spinal arteriovenous fistula, most prominently being fed a radicular artery arising from the right vertebral artery with only ventral venous drainage.
RESULTS: This feeder was selected and embolized with onyx, however residual fistula persisted and the patient subsequently underwent microsurgical disconnection. At six-month follow-up, patient motor deficits have resolved and difficulty with proprioception is improving.
CONCLUSION: Type I dural arteriovenous fistulae are associated with dorsal venous drainage. Our case demonstrates an exception to this. Recognizing this exception was crucial, because it allowed for simple microsurgical disconnection. We propose that type I dural arteriovenous fistulae be subdivided into ventral and dorsal based on their drainage pattern. This differentiation is critical because lesions with ventral drainage have traditionally been classified as type IV. These lesions have a different treatment method given involvement of spinal arteries.