Intracranial pseudoaneurysm due to rupture of a saccular aneurysm mimicking a large partially thrombosed aneurysm (“ghost aneurysm”)

Intracranial pseudoaneurysm formation due to ruptured non-traumatic saccular aneurysm is extremely rare. We experienced two cases of large pseudoaneurysm formation due to rupture of a saccular aneurysm. The neuroradiological ghost-like appearance of the aneurysms led to misdiagnoses as large partially thrombosed aneurysm. Two cases of large intracranial pseudoaneurysm formation due to rupture of a saccular aneurysm occurred in a 77-year-old comatose woman with an aneurysm on the anterior wall of the internal carotid artery and a 73-year-old comatose woman with an anterior cerebral artery (azygos) aneurysm. Both patients suffered subarachnoid hemorrhage associated with intracerebral and intraventricular hematomas. Angiography showed peculiar “ghost-like” appearance of the aneurysm including delayed filling, changing shape, retention of the contrast material after the venous phase, and unclear location of neck. Neck clipping surgeries were performed, but were difficult because of the preoperative misdiagnosis as large partially thrombosed aneurysm. The entity of “ghost aneurysm” caused by rupture of a saccular aneurysm should be considered in the clinical diagnosis.