Which posterior fossa tumor may show cerebellar peduncle involvement on imaging?

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

Answer: (A)

Medulloblastoma is the tumor most likely to involve the cerebellar peduncles on imaging. This tumor tends to arise in the cerebellar vermis in children and is highly aggressive, with a propensity to extend beyond the tumor bed into adjacent structures and along CSF pathways. Its growth pattern often brings it into the surrounding brainstem regions, including the peduncles, which can be seen on MRI as invasion or contact with the superior or inferior cerebellar peduncles, sometimes with diffusion restriction due to high cellularity.

Pilocytic astrocytoma is usually more well-circumscribed and often presents as a cystic lesion with a enhancing mural nodule, and it tends to spare deep invasion of peduncular pathways. Ependymoma arises near the fourth ventricle and may extend into adjacent spaces, but the classic pattern is ventricle-centered growth rather than peduncular invasion. Cerebellar astrocytoma is not a typical descriptor for a common posterior fossa tumor pattern and does not usually emphasize peduncular involvement.