Differentiation in the medulloblastoma. A histological and immunohistochemical study.

The histological and immunohistological features of medulloblastomas were investigated in patients participating in an ongoing cooperative study of the Societé International d'Oncologie Pédiatrique (SIOP). Of 51 neoplasms, four were the classic desmoplastic variant. In regard to the histological features used to grade neoplasms, considerable inter- and intratumoral variation was observed. The neoplasms with the most pleomorphic and coarsely structured nuclei tended to be neuroblastic, whereas the most delicate and uniform nuclei were found in the desmoplastic neoplasms. Twenty-one of the cases exhibited neuroblastic differentiation in the form of neuroblastic rosettes. Of these, three also contained neoplastic ganglion cells. Of the five medulloblastomas that were calcified, four contained neuroblastic rosettes in accord with the tendency for calcification in neuroblastic neoplasms. In many of the neuroblastic neoplasms, islands of markedly neuron-specific enolase (NSE)-positive cells were seen. Although the limited specificity of this marker enzyme is recognized, we believe that this focal intense staining could indicate neuronal differentiation somewhat more advanced than in small NSE-positive islands of reduced cellularity, many of which were strongly positive. The nuclei in these island were usually larger and more vesicular than those in the surrounding densely cellular areas. These features and the frequent association with Homer-Wright rosettes suggest that these foci represent a form of neuronal differentiation. Astrocytic differentiation was more difficult to define and required the use of staining for glial fibrillary acidic protein (GFAP). Six neoplasms contained GFAP-positive cells that were clearly neoplastic. Many others contained scattered reactive astrocytes and dispersed cells whose neoplastic versus reactive nature could not be defined.(ABSTRACT TRUNCATED AT 250 WORDS)