The histological changes that occur in brain tissue have rarely been documented in patients with dural arteriovenous fistulas (AVFs). In this study the authors report on two patients with dural AVFs in the transverse-sigmoid sinus who presented with subarachnoid hemorrhage or progressive dementia. Histological studies of the cerebellar cortices showed a selective loss of Purkinje cells, indicating an ischemic insult caused by venous hypertension. Admission N-isopropyl-p-123I-iodoamphetamine single-photon emission computerized tomography scans demonstrated a decrease in cerebral blood flow, including flow through the cerebellum. Venous hypertension caused by transverse-sigmoid sinus dural AVFs provokes an ischemic condition severe enough to cause selective neuronal damage in the cerebellum.