Extracranial aneurysm of the posterior inferior cerebellar artery: case report.

The authors report the unusual case of an aneurysm arising from the extracranial portion of the left posterior inferior cerebellar artery (PICA). The patient was a 39-year-old woman who developed a subarachnoid hemorrhage. The hemorrhage was in the basal, ambient, and Sylvian cisterns, but not in the ventricles. There were no focal neurological deficits, and the clinical grading was 1. On cerebral angiograms, the PICA was found to originate from the vertebral artery as low as 17.9 mm below the foramen magnum and to enter into the spinal canal through the intervertebral foramina of C1-C2. The artery went up to the posterior fossa and had only the cranial loop with an absence of the caudal loop. The saccular aneurysm hung on the initial segment of the PICA and was located at the C1 level. The patient developed motor aphasia and hemiparesis on the right side 15 days after onset, and an infarction was disclosed in the boundary zones of the left parietal lobe on a computed tomographic scan. The aneurysm was successfully obliterated by a neck clipping 2 months later, and the patient was discharged in good condition. The literature discussing PICA aneurysms in the extracranial, as well as distal, portion is reviewed.