Purpose or Case Report: Our purpose is to show representative cases of CNS (Central Nervous System) embryonal tumors in children with discussion of the new WHO (World Health Organization) classification system recently issued in 2016.
Methods & Materials: According to the prior WHO CNS tumor classification in 2007, intracranial embryonal tumors included medulloblastoma, PNET (primitive neuroectodermal tumor), and ATRT (atypical teratoid-rhabdoid tumor). All are grade IV tumors by WHO grading system. Medulloblastoma is the most common infratentorial tumors in children. ATRT is much less common and it can be seen either as supratentorial tumors or as the posterior fossa tumors. PNETs are uncommon hemispheric tumors, histologically similar to medulloblastoma, ATRT or pinealoblastoma. We reviewed imaging findings of each embryonal tumor on CT and MRI, focused on differential points. Changes in the new classification system were also reviewed.
Results: Most medulloblastomas and the solid components of PNETs and ATRT show characteristic findings of the highly cellular tumors, that is, high attenuation on unenhanced CT and hypointensity on MR T2WIs with diffusion restriction. ATRT is younger in ages, more laterally positioned, and frequently showing cystic or hemorrhagic component on imaging studies as compared to medulloblastoma. PNETs are usually large, deep seated, heterogeneous tumors with necrosis or hemorrhage; less mass effect or surrounding edema than expected for large tumor size.
There have been many changes in the new CNS tumor classification system issued in 2016. For the embryonal tumors, PNET has been removed from the list and medulloblastomas have been subclassified by means of genetic definition. ATRT remains unchanged.
Conclusions: Medulloblastoma and ATRT remain in the CNS embryonal tumor list but PNET may fade away from our memory. Knowledge about imaging characteristics of the intracranial embryonal tumors and the new classification system will help us to diagnose and manage these highly malignant CNS tumors.