Pial AVMs are thought to be congenital fed by branches of the intracranial circulation but may become mixed pial-dural if they parasitize the external carotid artery or muscular branches of the vertebrals. 98% of pial AVMs are solitary and 85% are supratentorial and may be multiple in Osler-Weber-Rendu and Wyburn-Mason syndromes. 10% are complicated by aneurysms and have an annual risk of bleeding of 2-4%. 1/2 present with hemorrhage, another 1/4 with seizures. This was a completely pial AVM with cortical venous drainage via the anastomotic veins of Trolard and Labbe. The presence of cortical (vs deep) venous drainage raises the risk of hemorrhage. Related Cases
