A 5-year-old boy has two months of morning headache and projectile vomiting. MRI shows a heterogeneously enhancing midline cerebellar mass filling the fourth ventricle, with markedly restricted diffusion on DWI. Which is the most likely diagnosis?

• A Juvenile pilocytic astrocytoma
• B Brainstem glioma
• C Fourth ventricular ependymoma
• D Medulloblastoma ✓

Explanation

Medulloblastoma is a highly cellular small round blue cell tumour of the vermis or fourth ventricle in children, so it shows marked restricted diffusion on DWI. Pilocytic astrocytoma typically has low cellularity with free diffusion and often a cyst with a mural nodule. Ependymoma enhances variably and characteristically extends through the foramina of Magendie and Luschka rather than showing restricted diffusion.

Reference: Osborn's Brain, 2nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.