A dominant left vertebral artery supplies a large left PICA. A 3.0 x 2.5mm aneurysm arises from the distal left PICA, pointing posteriorly. A branch of the PICA then goes on to supply a tangle of abnormal vessels measuring approximately 1cm diameter, located adjacent to the medial left transverse sinus. This results in early venous shunting into the transverse sinus, with some reflux into the contralateral sinus. Branches from the left posterior cerebral, superior cerebellar and posterior meningeal arteries also appear to supply the vascular malformation. The right vertebral artery is hypoplastic, predominantly terminating in the right PICA with only minor supply to the basilar artery. There is no significant left AICA demonstrated. No supply from the anterior circulation is vident.
Comment: Probable left posterior fossa pial AVM with supply from left PICA, PCA and SCA, and 3mm flow related left PICA aneurysm representing the likely source of IVH.