 MRI:There is metallic artifact along the right petrous apex, which may be related to embolization material. There is a left transfrontal ventriculostomy shunt catheter which terminates adjacent to the right frontal horn.There is a relatively round lesion involving the pons, medulla and right middle cerebellar peduncle causing leftward displacement of the fourth ventricle. This lesion has a complex mixed signal appearance on T2-weighted and FLAIR imaging and susceptibility hypointensity, suggestive of a collection of blood products. There is associated edema within the brainstem. The cerebellar tonsils are at or slightly below the foramen magnum. On the prior examinations, the involved parenchyma was distorted and hemosiderin stained presumably due to prior hemorrhage. In addition, the fourth ventricle was somewhat cystically expanded.No evidence of midline shift or acute infarction. The ventricles are small in caliber. Flow-voids are present within the major vessels indicating patency. There is scattered opacification of ethmoid air cells and complete opacification of the sphenoid sinuses. There is mild mucosal thickening of the bilateral maxillary sinuses. Prior right parietal mastoidectomy is noted. Calvarium and extracranial soft tissues are grossly unremarkable.MRA:Immediately above the hemorrhagic collection, there is a network of small faintly flow enhancing structures which could reflect residual AVM based on the history and which appears similar to that seen on the prior exam. The right AICA is prominent and courses along this lesion potentially representing part of its vascular supply. No obvious large draining vein is seen. Outside of this lesion, no additional aneurysm or vascular malformation is suspected. The vessels otherwise demonstrate normal caliber and morphology.
Findings compatible with hemorrhage involving the brainstem, primarily the pons and medulla. Immediately above this hemorrhage is a network of faintly flow enhancing structures which could reflect residual AVM based on the history, although other vascular lesions could potentially have this appearance as well. The round and well contained margins of the hematoma suggest that this could represent hemorrhage into a pre-existing cystic cavity, or potentially a large thrombosed pseudoaneurysm. No definite evidence of additional aneurysms is seen on this study.Findings were discussed with Dr. Braverman at 4:00 PM on 12/19/2016.