Primitive neuroectodermal tumor arising in long-standing cerebellar atrophy.

Primitive neuroectodermal tumors (PNETs) account for one fifth of childhood brain tumors. Although little is known of the pathobiology of this tumor type, there are associations with both genetic syndromes and exposures to specific environmental agents. Progressive cerebellar atrophy predating the presentation of a primary brain tumor, in the absence of a genetic syndrome, has not been reported with PNETs. We report a case of a posterior fossa PNET occurring in association with long-standing cerebellar atrophy without evidence of a genetic syndrome. This case may represent an unrecognized paraneoplastic syndrome or a unique subtype of PNET.