A clinicopathologic reappraisal of brain stem tumor classification - Identification of pilocytic astrocytoma and fibrillary astrocytoma as distinct entities

BACKGROUND. Brain stem tumors in children have been classified pathological ly as low grade or high grade gliomas and descriptively as diffuse gliomas, intrinsic gliomas, midbrain tumors, tectal gliomas, pencil gliomas, dorsal exophytic brain stem tumors, pontine gliomas, focal medullary tumors, cerv icomedullary tumors, focal gliomas, or cystic gliomas. METHODS, To search for a simplified and prognostic clinicopathologic scheme for brain stem tumors, the authors reviewed a consecutive cohort of patien ts younger than age 21 years with tumors diagnosed from 1980 through 1997. Pathology specimens and neuroimaging were classified by masked review. Stat istical and survival analysis along with Cox proportional hazards regressio n was performed. RESULTS. Seventy-six patients were identified, with initial diagnostic magn etic resonance imaging available for 51 and pathology specimens for 48 pati ents. Twenty cases were classified histologically as pilocytic astrocytoma (PA), 14 as fibrillary astrocytoma (FA), and 14 as other tumors or indeterm inate pathology. For all tumors, characteristics significantly associated w ith a worse survival rate were: symptom duration less than 6 months before diagnosis (P = 0.004); abducens palsy at presentation (P < 0.0001); pontine location (P = 0.0002); and engulfment of the basilar artery (P = 0.006). P ilocytic astrocytoma was associated with location outside the ventral pens (P = 0.001) and dorsal exophytic growth (P = 0.013); Fibrillary astrocytoma was associated with symptoms less than 6 months (P = 0.006), abducens pals y (P < 0.001), and engulfment of the basilar artery (P = 0.002). Pilocytic astrocytoma showed 5-year overall survival (OS) of 95% (standard error [SE] , 5%) compared with FA 1-year OS of 23% (SE, 11%;P < 0.0001). CONCLUSIONS. Brain stem tumors can be succinctly and better biologically cl assified as diffusely infiltrative brain stem gliomas-generally FA located in the ventral pens that present with abducens palsy, often engulf the basi lar artery, and carry a grim prognosis-and focal brain stem gliomas-frequen tly PA arising outside the ventral pens, often with dorsal exophytic growth , a long clinical prodrome, and outstanding prognosis for survival. Our fin dings emphasize the individuality of PA as a distinct clinicopathologic ent ity with an exceptional prognosis. Cancer 2000; 89:1569-76. (C) 2000 Americ an Cancer Society.