Unilateral isolated hypoglossal nerve palsy due to pathologically adherent PICA fusiform aneurysm – A case report

BACKGROUND Isolated hypoglossal nerve palsy due to mechanical compression by a vascular lesion is rare. CASE DESCRIPTION We report the case of a 72-year-old man who presented with a 4-year history of swallowing disturbance and subsequently progressively worsening left-sided tongue atrophy. He was referred to our department by a neurologist due a magnetic resonance imaging detected left vertebral artery compression of the medulla. Neurological examination was unremarkable except for left hypoglossal nerve dysfunction, which presented as left-sided atrophy and impaired movement of the tongue. Three-dimensional computed tomography angiography showed proximal left posterior inferior cerebellar artery (PICA) origin fusiform aneurysm. Microvascular decompression was done through a left transcondylar fossa approach. Intraoperative findings were thickened arachnoid around the lower cranial nerves, fusiform aneurysm of the left PICA at its origin from the left vertebral artery which was severely adherent to and compressing the left hypoglossal nerve rootlets. CONCLUSION The PICA has a very close relationship to the hypoglossal nerve, and its fusiform dilatation could cause isolated hypoglossal nerve dysfunction. Pathological adhesions between hypoglossal rootlets and the PICA aneurysm wall could be a possible contributor in the development and progression of hypoglossal nerve palsy.