High flow pial arteriovenous fistula with dural sinus malformation of the posterior circulation.

Posterior fossa congenital pial arteriovenous fistulas are rare vascular anomalies associated with high morbidity. These anomalies often present challenges to neurointerventionists due to their complex morphological features. We successfully treated two technically challenging, infratentorial large pial arteriovenous fistulas (AVFs) associated with complete flow steal in the basilar artery. The first case involved an 18-year-old male with a posterior fossa single-hole AVF characterized by dilated venous pouches and retrograde venous reflux. After an unsuccessful initial coiling attempt, this patient was treated using a double microcatheter coiling technique, supported by a large balloon for flow control. The second case involved a 9-month-old infant with a complex two-hole posterior fossa pial AVF and a large venous sac. This patient was treated with coil embolization of the fistula and with balloon protection of the vertebrobasilar junction. Both patients recovered without postoperative complications and showed significant improvement on follow-up. These cases provide valuable insights into the management and characteristics of pial arteriovenous fistulas.