Acta Neuropathol (2012) 123:465–472 467 Fig. 1 Dendrogram depicting the classiﬁcation of embryonal tumors of the cerebellum. Medulloblastomas should be differentiated from the less common ATRTs and ETANTRs of the cerebellum. Under the current consensus classiﬁcation of medulloblastoma four principle subgroups are identiﬁed: Wnt, Shh, Group 3, and Group 4. The evidence suggests that each of the four principle subgroups will likely have distinct ‘subsets’ that are biologically and clinically homogeneous as compared to other subsets from within the same subgroup. As the nature and number of subsets for each subgroup are currently unknown, the consensus classiﬁcation suggests that each subset be named using a Greek letter (a, b, c, etc.) until such time as they are sufﬁciently characterized to be named based on their molecular etiology Fig. 2 Comparison of the various subgroups of medulloblastoma including their afﬁliations with previously published papers on medulloblastoma molecular subgrouping support an etiological role for canonical Wnt signaling in the pathogenesis of this group of tumors, and lead to the nomenclature of ‘Wnt subgroup medulloblastomas’. Nearly all of the Wnt medulloblastomas studied to date have classic histology. Wnt medulloblastomas are fre- quently described as having CTNNB1 mutations, nuclear 123