Heterogeneity of extraparenchymal primitive neuroectodermal tumors within the craniospinal axis

Four cases of primitive neuroectodermal tumors (PNETs) with unusual localization (three intraspinal extramedullary and one pontocerebellar) are reviewed. Histologically, they were small round blue cell tumors with diverse patterns. Immunohistochemically, all tumors were positive for at least two neuronal markers, two cases were Mic-2 positive and one showed glial differentiation. The paraffin-embedded tumor specimens were examined by interphase FISH using dual-color probes specific for EWS, HER-2 and BCR loci. Molecular cytogenetic study revealed the presence of EWS rearrangement in two cases and the presence of i(17q) in one tumor. Three tumors exhibited 22 disomy and one was 22 polyploid. Extraparenchymal PNETs within craniospinal axis are heterogeneous from the clinical, histological, immunohistochemical and molecular point of view. These PNETs can be of a central or peripheral type. Multidisciplinary approach is of a basic importance in differential diagnosis of such cases.