Which tumor arises in the fourth ventricle and commonly presents with hydrocephalus and calcifications?

• A. Pilocytic astrocytoma
• B. Ependymoma
• C. Medulloblastoma
• D. Cerebellar astrocytoma

Answer: (B)

Think about where the tumor grows and what it does to CSF flow. When a child has a mass in or near the fourth ventricle that leads to hydrocephalus, and imaging shows calcifications, the most fitting diagnosis is an ependymoma. Ependymomas arise from the ependymal lining of ventricles, and in children they frequently involve the fourth ventricle. This location explains the obstructed CSF flow and resulting hydrocephalus. Calcifications are a common radiologic feature of ependymomas.

Other posterior fossa tumors fit less well. A pilocytic astrocytoma is typically a cerebellar lesion that often appears cystic with a mural nodule and calcifications are not defining. Medulloblastoma can also cause hydrocephalus by obstructing CSF, but it usually presents as a solid midline vermian mass with fewer calcifications and a different imaging profile. Cerebellar astrocytoma isn’t as strongly tied to the fourth ventricle with calcifications.

So the combination of fourth-ventricle origin, hydrocephalus, and calcifications most specifically points to an ependymoma.