Occlusion of the posterior communicating artery mimicking cerebral aneurysm: case report.

We report a rare case of posterior communicating artery occlusion mimicking a cerebral aneurysm. A 62-year-old man was admitted to Towakai Hospital with sudden onset of left motor weakness. He had developed thunderclap headache five days before. Computed tomographic scan and lumbar tap were negative for subarachnoid hemorrhage (SAH). Digital subtraction angiography and three-dimensional computed angiography showed aneurysmal protrusion at the junction of the right internal carotid (IC) artery and posterior communicating artery (PcomA). Because minor bleeding from IC-PcomA junction aneurysm was strongly suspected, a pterional craniotomy was performed. At surgery, there was no evidence of SAH but the PcomA was occluded at the peripheral portion. Several perforators arose from the proximal portion of the PcomA. An aneurysmal protrusion especially without a prominent PcomA does not always indicate an IC-PcomA aneurysm. In diagnosing protruding vascular lesions at the bifurcation between the IC-PcomA, not only infundibular dilatation but also occlusion of the PcomA should be considered if the PcomA is not visualized.