ROSETTE-FORMING GLIONEURONAL TUMOR

Abstract

Rosette-forming glioneuronal tumor is a rare, rather recently described tumor featuring a highly distinctive, biphasic histological pattern, including a cytologically uniform neuronal component of Homer-Wright type pseudorosettes and an accompanying astrocytic element resembling pilocytic astrocytoma. Its occurrence in the posterior fossa and association with the fourth ventricle is stereotypical and a feature of all reported cases. In this article, we describe the first rosette-forming glioneuronal tumor arising outside this site, a histologically classic example involving the anterior visual pathway and associated with neurofibromatosis type 1. Genetic (fluorescent in situ hybridization) studies demonstrated no large deletion in either normal or neoplastic tissue, indicating that the genetic abnormality underlying neurofibromatosis type 1 in this patient is likely a very small deletion or point mutation. The relation of the tumor to the underlying neurofibromatosis type 1 cannot be assessed.