The Tale of Two Hedgehogs: Central Nervous System Embryonal Tumor Diagnosis in 3 Acts

Abstract Primitive embryonal tumors of the central nervous system have undergone considerable evolution in their categorization in the past century—most rapidly in the past decade with the application of molecular pathology in diagnosis. This presents numerous practical considerations when encountering one of these tumors. One may need to utilize multiple techniques to come to a prognostically accurate and actionable diagnosis. We review two cases, both with the final diagnosis of “medulloblastoma, SHH activated and TP53 wild type (World Health Organization grade IV).” These diagnoses were each arrived upon using separate, valid approaches, with consideration of the histological differential diagnosis. Immunohistochemistry, next-generation sequencing, and methylation array analysis are each presented with practical considerations of when they are most useful.