Imaging description

Posterior fossa tumors account for approximately 50% of pediatric brain tumors [1]. While supratentorial location predominates in infants, infratentorial tumors are more frequent in children older than 4 years of age [2]. Common pediatric posterior fossa tumors include juvenile pilocytic astrocytoma (JPA), ependymoma, medulloblastoma (MB), and brainstem gliomas; uncommon tumors include atypical teratoid rhabdoid tumor (ATRT), glioblastoma, hemangioblastoma, and gangliocytoma. Essentially all of these tumors with the exception of brainstem gliomas either arise from or secondarily involve the cerebellum.

MB is the most common childhood CNS tumor, accounting for 12–25% of all childhood CNS tumors (Fig. 23.1) [3]. MBs are associated with a rapid growth and early subarachnoid spread that may extend into the spinal canal. Different histologic subtypes exist; the great majority of MBs arise from midline inferior vermis and exhibit a classic histologic type, whereas desmoplastic MBs tend to occur off-midline and in older children. Children less than 3 years of age have an inferior survival rate [4]. Typical imaging features of MBs include hyperdensity on CT, decreased T2 signal and elevated DWI signal with accompanying decreased apparent diffusion coefficient (ADC) values. About half of MBs include cysts and non-enhancing regions.