Which pediatric brain tumor most commonly presents with obstructive hydrocephalus?

• A. Pilocytic astrocytoma
• B. Medulloblastoma
• C. Optic pathway glioma
• D. Ependymoma

Answer: (B)

Obstructive hydrocephalus happens when CSF flow is blocked within the ventricular system, most often at or near the fourth ventricle. In children, a cerebellar tumor that grows rapidly right in the midline—the cerebellar vermis—tends to block that fourth ventricle, causing noncommunicating hydrocephalus. Medulloblastoma is the classic posterior fossa tumor in the pediatric population that does just that: its location and aggressive growth readily impede CSF pathways, leading to signs of increased intracranial pressure such as headaches and vomiting, and sometimes ataxia from cerebellar dysfunction. While other tumors in the posterior fossa can cause hydrocephalus as well, medulloblastoma most classically presents with obstructive hydrocephalus in children, making it the best fit for this scenario.