Subarachnoid Hemorrhage Due to Ruptured Intracranial Aneurysm Arising from a Vertebral Artery-Bihemispheric Posterior Inferior Cerebellar Artery Bifurcation

Abstract

Although the anatomy of the posterior inferior cerebellar artery (PICA) is highly variable, a solitary PICA supplying both hemispheres of the cerebellum is rare. A 76-year-old woman presented with severe headache and subsequent loss of consciousness and was admitted to our hospital. Initial computed tomography showed subarachnoid hemorrhage. Three-dimensional digital subtraction angiography revealed a saccular aneurysm arising from the right vertebral artery (VA)-PICA bifurcation. The PICA branching from the right VA was enlarged, tortuous, and crossed the midline to supply both cerebellar hemispheres. This right PICA was interpreted as a bihemispheric PICA. Recognizing this variant preoperatively could help prevent complications of surgery. Careful follow-up studies are necessary in cases with bihemispheric PICA to monitor for the development of aneurysm at the junction between the bihemispheric PICA and the VA or the distal portion of the bihemispheric PICA.

Keywords: Aneurysm; bihemispheric posterior inferior cerebellar artery; subarachnoid hemorrhage; variant.

Figure 1

(a) Preoperative three-dimensional digital subtraction angiogram, posteroanterior view, showing an enlarged and tortuous right PICA (dotted white arrow) crossing the midline to supply both cerebellar hemispheres (white arrowheads). (b) Three-dimensional digital subtraction angiogram, oblique view, showing a small saccular aneurysm arising from the right VA-PICA bifurcation (red arrow). (c) Three-dimensional digital subtraction angiogram, superoinferior view, showing the arterial course of a cortical branch originating from the right PICA (white arrow). (d) Three-dimensional digital subtraction angiogram, oblique view, showing a large branch distal to the choroidal point (white arrow), which gives rise to the ipsilateral vermian branch (*) and then crosses the midline. The artery crossing the midline gives rise to the contralateral vermian (‡) and hemispheric branches (††). BA: Basilar artery, L: Left, PICA: Posterior inferior cerebellar artery, R: Right, VA: Vertebral artery, †: Right hemispheric branch of the bihemispheric PICA, ††: Left hemispheric branch of the bihemispheric PICA

Figure 2

(a and b) Intraoperative photographs showing an enlarged and tortuous right posterior inferior cerebellar artery (black arrows) and its relationship to the ipsilateral cerebellum, vertebral artery, lower cranial nerves (white arrow: cranial nerve XI; white arrowheads: cranial nerves IX and X), medulla oblongata, and aneurysm (*). (c) The aneurysm is occluded by a slightly curved Yasargil titanium mini clip (No. FT712T) following temporary occlusion of the right vertebral artery by a temporary clip. (d) Intraoperative indocyanine green angiogram showing patency of the right PICA. MO: Medulla oblongata, VA: Vertebral artery, R: Right