PREDOMINANCE OF PILOCYTIC HISTOLOGY IN DORSALLY EXOPHYTIC BRAIN-STEM TUMORS

We report the magnetic resonance imaging (MRI) and clinicohistologic c haracterization of dorsally exophytic brain stem gliomas (DEBSGs). Bet ween 1983 and 1991, 12 of 51 patients evaluated for the diagnosis of b rain stem glioma were found to have DEBSGs emanating from the pens, po ntomedullary junction or medulla. Eleven of the 12 patients had classi c juvenile pilocytic astrocytomas. Unlike most other brain stem tumors , these patients were young (median 38 months, range 17-75), had a rel atively long duration of symptoms (median 7 months, range 2-24) and di splayed signs of increased intracranial pressure with Limited cranial nerve paresis, absence of pyramidal tract findings, and near normal br ain stem auditory-evoked potentials. MRI characteristically showed sha rply demarcated lesions with decreased signal intensity on T1, and inc reased intensity on T2 sequences. Except for cystic areas, these tumor s showed bright, uniform enhancement after gadolinium-DTPA. In all pat ients, 50-100% of the tumor volume could be resected. Three of 10 pati ents who received no immediate postoperative treatment eventually demo nstrated disease progression, and 2 patients with subtotal resections who were treated with radiation and/or chemotherapy postoperatively re main disease-free for extended periods of time. The only death occurre d in the 1 patient treated with chemotherapy who died of secondary leu kemia. The overall and progression-free survival of these patients at 2 years is 100 and 67% as compared to 18 and 21%, respectively, for ot her concomitantly treated non-exophytic brain stem gliomas. The excell ent prognosis for this unusual group of brain stem tumors may be assoc iated with the generally benign biology of pilocytic tumors and the ab ility to achieve significant degrees of resection.