Lobar pilocytic astrocytomas of the cerebral hemispheres: I. Diagnosis and nosology.

This study provides neuropathological and neuroradiological observations on 11 cases of lobar pilocytic astrocytomas of the cerebral hemispheres, reappraising potential diagnostic caveats. These tumors may show variable degrees of contrast enhancement on computed tomography, as well as gadolinium uptake on magnetic resonance imaging, making them indistinguishable from malignant gliomas. Histopathologically, although typically pilocytic, they may exhibit areas of increased cellular density with protoplasmic and multinucleated glial elements (pilo-protoplasmic astrocytoma). The presence and particularly the abundance of distinct gliodegenerative structures, i.e. eosinophilic granular bodies (EGBs) and to a lesser degree Rosenthal fibers, in conjunction with collateral clinical, histologic and imaging parameters may facilitate oncotypic diagnosis. Mixed pilocytic and fibrillary astrocytomas are recognized, while malignant change may also rarely occur in longstanding lobar pilocytic astrocytomas.