Intraosseous Arteriovenous Fistula of the Mastoid Emissary Canal Treated with Combined Transvenous and Transarterial Embolization: A Case Report.

Objective: The mastoid emissary veins (MEVs) traverse the mastoid emissary canal (MEC) and connect the sigmoid sinus to the extracranial venous system. Although MEVs are frequently identified on angiography, an intraosseous arteriovenous fistula (AVF) arising primarily within the MEC has not been previously reported. Herein, we report a rare case of intraosseous AVF of the MEC that was successfully treated using a combined endovascular approach. Case Presentation: A 70-year-old woman presented with progressive left-sided pulsatile tinnitus. DSA revealed an intraosseous AVF localized in the left MEC. The fistula was supplied by the occipital and ascending pharyngeal arteries, with retrograde drainage into the sigmoid sinus and ipsilateral transverse sinus and antegrade drainage into the extracranial subcutaneous veins, without cortical venous reflux. Because the shunt point was located in a short osseous canal adjacent to a patent sigmoid sinus, transarterial embolization (TAE) alone posed a high risk of embolic migration. Therefore, transvenous coil embolization was performed first to protect the sinus, followed by TAE using Onyx (Medtronic, Irvine, CA, USA). Complete obliteration of the fistula was achieved without compromising the sigmoid sinus. Conclusion: The present case represents a previously unreported intraosseous AVF confined to the MEC. For fistulas located in short bony venous segments adjacent to a functional sinus, a combined transvenous embolization and TAE strategy may be a safe and effective option.