MCQ: Headache | Vomiting | ataxia | posterior fossa mass

Correct answer: C Medulloblastoma

Explanation: Medulloblastoma 

This child most likely has medulloblastoma, the most common malignant brain tumor of childhood.

The diagnosis is supported by the following findings:

• Progressive early morning headaches and recurrent vomiting, suggesting raised intracranial pressure
• Papilledema, indicating increased intracranial pressure
• Truncal ataxia, horizontal nystagmus, and gait instability, indicating a midline cerebellar lesion
• MRI demonstrating a midline posterior fossa mass compressing the fourth ventricle, resulting in obstructive hydrocephalus

Medulloblastoma is an embryonal tumor that typically arises from the cerebellar vermis in school-aged children. Compression of the fourth ventricle leads to obstructive hydrocephalus, which accounts for the symptoms of raised intracranial pressure. Because medulloblastoma has a tendency to spread through the cerebrospinal fluid (CSF), staging requires MRI of the entire neuraxis and CSF cytology (performed after relief of raised intracranial pressure when it is safe).

Why the other options are incorrect

A. Atypical teratoid/rhabdoid tumor (ATRT)
ATRT usually occurs in children younger than 3 years and is highly aggressive. Although it may arise in the posterior fossa, the patient’s age and imaging findings are more typical of medulloblastoma.

B. Ependymoma
Ependymomas commonly arise from the floor of the fourth ventricle and may also cause obstructive hydrocephalus. However, they are generally centered within the ventricle, whereas a midline cerebellar mass in a school-aged child is more characteristic of medulloblastoma.

C. Medulloblastoma
Correct. The combination of raised intracranial pressure, cerebellar signs, and a midline posterior fossa mass is classic for medulloblastoma.

D. Diffuse intrinsic pontine glioma (DIPG)
DIPG presents with cranial nerve palsies, long tract signs, and ataxia due to an infiltrative pontine lesion. MRI shows diffuse enlargement of the pons rather than a discrete posterior fossa mass causing hydrocephalus.

E. Pilocytic astrocytoma
Pilocytic astrocytoma is the most common overall pediatric brain tumor and usually arises in the cerebellar hemisphere. MRI typically demonstrates a cystic lesion with an enhancing mural nodule, rather than a solid midline mass compressing the fourth ventricle.

Learning Point

In a school-aged child presenting with:

• Early morning headache
• Recurrent vomiting
• Papilledema
• Truncal ataxia
• A midline posterior fossa mass with obstructive hydrocephalus

the most likely diagnosis is medulloblastoma. A key examination point is that medulloblastoma frequently spreads through the CSF (“drop metastases”), so MRI of the entire spine is an essential part of staging before definitive treatment.