<unk> s are usually found in the vicinity of the fourth ventricle, between the brainstem and the cerebellum. Tumors with similar appearance and characteristics originate in other parts of the brain, but they are not identical to<unk> . Although<unk> s are thought to originate from immature or embryonal cells at their earliest stage of development, the cell of origin depends on the subgroup of<unk> . WNT tumors originate from the lower rhombic lip of the brainstem, while SHH tumors originate from the external granular layer. Currently,<unk> s are thought to arise from cerebellar stem cells that have been prevented from dividing and differentiating into their normal cell types. This accounts for the histologic variants seen on biopsy. Both perivascular pseudorosette and Homer Wright pseudorosette formations are highly characteristic of<unk> s and are seen in up to half of cases. The classic rosette with tumor cells around a central lumen can be seen. In the past,<unk>  was classified using histology, but recent integrated genomic studies have revealed that<unk>  is composed of four distinct molecular and clinical variants termed WNT/β-catenin, Sonic Hedgehog, Group 3, and Group 4. Of these subgroups, WNT patients have an excellent prognosis and group 3 patients have a poor prognosis. Also, a subgroup-specific alternative splicing further confirms the existence of distinct subgroups and highlights the transcriptional heterogeneity between subgroups. Amplification of the Sonic Hedgehog pathway is the best characterized subgroup, with 25% of human tumors having mutations in Patched, Sufu (Suppressor of Fused Homolog), Smoothened, or other genes in this pathway.<unk> s are also seen in Gorlin syndrome as well as Turcot syndrome. Recurrent mutations in the genes CTNNB1, PTCH1, MLL2, SMARCA4, DDX3X, CTDNEP1, KDM6A, and TBR1 were identified in individuals with<unk> . Additional pathways disrupted in some<unk> s include MYC, Notch, BMP, and TGF-β signaling pathways.
Medulloblastoma
Sialoblastoma
Pineoblastoma
Ameloblastoma
Hemangioblastoma
Glioblastoma
Neurothekeoma
Subependymoma