A case of medulloblastoma in a patient with fetal ventricular enlargement.

Medulloblastoma is the second-most common malignant tumor in children. Medulloblastoma has been categorized into four distinct molecular subgroups: WNT, sonic hedgehog (SHH), group 3, and group 4. We report on a male child with medulloblastoma, in whom an enlarged ventricle was diagnosed in utero. Magnetic resonance imaging showed cyst formation in the cerebellar hemisphere initially, with tumor growth being indicated later. Tumor resection was performed when the boy was 12 months old. The histological findings showed extensive nodularity. Further genetic analysis revealed the tumor to be SHH type. This is the first description of a medulloblastoma observed from the fetal stage. Our findings in this case indicate that cyst formation may be the pre-neoplastic lesion of SHH-subtype medulloblastomas.