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 ex traparenchymal cerebellopontine angle (CPA) tumors of any sort are extremel y rare. Most gliomas encountered in the CPA in either children or adults in volve the CPA as exophytic extensions of primary brain stem and/or cerebell ar tumors. We encountered an unusual case of a giant CPA pilocytic astrocyt oma arising from the proximal trigeminal nerve, completely separate from th e brain stem. A nine-year-old girl with no evidence for any neurocutaneous syndrome, presented with headaches, mild obstructive hydrocephalus, trigemi nal hypesthesia and a subtle peripheral facial paresis. Pre-operative neuro imaging suggested a petroclival meningioma. The tumor was completely resect ed via a right pre-sigmoid, retro-labyrinthine, sub-temporal, transtentoria l ('petrosal') approach, using intraoperative neurophysiological monitoring , with minimal morbidity. This appears to be the first reported case of a p ediatric primary CPA glioma and the seventh reported case of primary CPA gl ioma, overall. It represents the second reported case of a primary CPA pilo cytic 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 o f histological studies of normal cranial nerves, we hypothesize that the po int of origin of these rare and unusual tumors is the root entry zone of th e involved cranial nerves. The differential diagnosis of primary CPA tumors should be expanded to include cranial nerve root entry zone primary CPA gl iomas.