[A case of repeated intracerebral hemorrhage due to a ruptured aneurysm of collateral circulation from the posterior cerebral artery to the middle cerebral artery].

We present a case of ruptured distal middle cerebral artery aneurysm associated with occlusion of the anterior trunk of the ipsilateral middle cerebral artery. An 83-year-old man had right homonymous hemianopsia and right mild hemiparesis. CT scan revealed hematoma and a perifocal low density area at the left occipital subcortex without subarchnoid hemorrhage (SAH). MRI showed repeated bleeding at the same location as the CT scan. Moreover, cerebral angiograms disclosed an aneurysm on the leptomeningeal anastomosis from the left posterior cerebral artery to the middle cerebral artery. The anterior trunk of the left middle cerebral artery was occluded at the origin. The aneurysm was not situated at the bifurcation and was trapped without new neurological complications. This case suggested that hemodynamic stress due to occlusion of the main artery contributed to the development of an aneurysm at the collateral artery. Even if intraparenchymal hematoma presents without SAH, and even if it is located at a rare site for aneurysms, we should inspect the source of bleeding considering factors preventing SAH arising from aneurysms.