O16 De-novo high-grade DAVFs following posterior fossa surgery: report of two cases

<h3>Introduction</h3> The etiology of dural arteriovenous fistulas (DAVFs) is largely attributed to the neovascularization of thrombus in sinus venous thrombosis (SVT). Surgery in the posterior fossa is associated with sigmoid sinus occlusion in 4-11% of cases. We present two cases of aggressive, high-grade DAVFs that developed after tumor surgery in the posterior fossa. <h3>Case Description</h3> A 47-year-old male presented with a right vestibular schwannoma that was removed using a trans-labyrinthine approach. The patient’s one-year FU MRI showed dilated cortical veins; a DSA demonstrated a DAVF. A 60-year-old female underwent a sub-occipital retrosigmoid approach for removal of a right petroclival meningioma. The patient presented four years later with headaches and balance problems; her MRI suggested a vascular malformation in the operated region which DSA confirmed. Both patients had high-flow AV shunting involving the sigmoid and transverse sinuses (SS, TS) with severe stenosis of the distal SS in one and occlusion of the SS in the other patient, and reflux into cortical and deep veins. The fistulous connections were approached by a transvenous cross-over technique allowing for staged coil occlusion. Complete occlusion of AV shunting was achieved without complications. <h3>Results</h3> Posterior fossa surgery is associated with SVT leading to secondary complications such as DAVFs. Although rare and clinically obscure in some patients with concomitant hearing loss, these fistulas are typically of a high-grade and aggressive nature, and therefore should be diagnosed and treated as early as possible. Routine late imaging FU in patients who underwent posterior fossa surgery should be considered. <h3>Disclosure of Interest</h3> no.