Cranial nerve root entry zone primary cerebellopontine angle gliomas: a rare and poorly recognized subset of extraparenchymal tumors.

With the exception of patients with neurofibromatosis type II, pediatric extraparenchymal cerebellopontine angle (CPA) tumors of any sort are extremely rare. Most gliomas encountered in the CPA in either children or adults involve the CPA as exophytic extensions of primary brain stem and/or cerebellar tumors. We encountered an unusual case of a giant CPA pilocytic astrocytoma arising from the proximal trigeminal nerve, completely separate from the brain stem. A nine-year-old girl with no evidence for any neurocutaneous syndrome, presented with headaches, mild obstructive hydrocephalus, trigeminal hypesthesia and a subtle peripheral facial paresis. Pre-operative neuroimaging suggested a petroclival meningioma. The tumor was completely resected via a right pre-sigmoid, retro-labyrinthine, subtemporal, transtentorial ('petrosal') approach, using intraoperative neurophysiological monitoring, with minimal morbidity. This appears to be the first reported case of a pediatric primary CPA glioma and the seventh reported case of primary CPA glioma, overall. It represents the second reported case of a primary CPA pilocytic astrocytoma. Given the findings in this case and the six other cases of primary CPA gliomas reported in the literature, as well as the results of histological studies of normal cranial nerves, we hypothesize that the point of origin of these rare and unusual tumors is the root entry zone of the involved cranial nerves. The differential diagnosis of primary CPA tumors should be expanded to include cranial nerve root entry zone primary CPA gliomas.