[Transient blindsight (type 2) after surgery for posterior cerebral artery aneurysm--case report]

In a 47-year-old woman experiencing pulsatile headache, radiological examination revealed a large right posterior cerebral artery (PCA) aneurysm. Preoperative neurological examination showed bilateral papilledema, but no visual disturbance. Cerebral angiography revealed that the aneurysm originated from the ambient segment of the PCA, and the posterior temporal, calcarine, and parieto-occipital arteries were all branched from the aneurysmal dome. Clipping of the feeding PCA trunk was performed via a left subtemporal approach. As a result of left occipital lobe infarction due to calcarine artery occlusion, right upper quadrant hemianopsia appeared after surgery, as confirmed by Goldman's perimetry. Other cerebral infarctions were identified in the junction between the left posterior internal capsule and thalamus, in the left posterior corpus callosum, and in the posterior base of the left temporal lobe due to the occlusion of the posterolateral thalamoperforating, posterior pericallosal, and posterior temporal arteries, respectively. The aneurysm was thrombosed and headache and papilledema subsided. The patient was able to detect the motion of a subject in a blind field, but consciousness of sight was absent. She was able to unconsciously move her finger toward a small penlight, and insert a paper into a slot with variable angles in the blind field. These phenomena disappeared within 4 months of the surgery. The results to forced choice tasks with figures (circle, cross, square, triangle, and star) and colors (red, blue, yellow, and green) were below chance levels. The present case was thus diagnosed as blindsight type 2 (gnosopsia) associated with awareness, probably due to transient activation of the dorsal "what" pathway among numerous visual processes.