Uncommon pediatric tumors of the posterior fossa: pathologic and molecular features

Three tumors are commonly encountered in the posterior fossa of children: pilocytic astrocytoma (PA), medulloblastoma (MB), and ependymoma. However, a variety of additional tumors may occasionally be appreciated. Appropriate and successful treatment of these less common cases is predicated upon correct pathologic diagnosis.

Reviewed herein are five less common tumors that may affect the posterior fossa of children: (1) “embryonal tumor with multilayered rosettes” (ETMR); (2) “cribriform neuroepithelial tumor” (CRINET); (3) “rosette-forming glioneuronal tumor” (RGNT); (4) “diffuse pilocytic astrocytoma” (dPA); and, (5) “desmoplastic small round cell tumor” (DSRCT). Each of the foregoing has a varying predilection for children and a posterior fossa location. For example, RGNT by definition arises in association with the 4th ventricle; while the mean age of those afflicted is 33, children may also be affected. Likewise, descriptions of dPA are generally restricted to the posterior fossa, and in particular, the cerebellum of children. Alternatively, DSRCT is a form of undifferentiated sarcoma that characteristically originates in the abdomen of children, but on occasion arises from the tentorium of young adults and children. The relevant molecular genetic underpinnings for each of the tumors highlighted herein have been well described and may carry diagnostic utility, not to mention clues as to underlying etiology.

A number of pediatric brain tumors have a tendency to occur in the posterior fossa. While far less common than PA, MB, or ependymoma, the entities highlighted herein appear to have a degree of proclivity for the posterior fossa of children and as such warrant due consideration in the clinicopathologic workup of these cases.