A 6-year-old boy presents with morning headaches, vomiting, and truncal ataxia over 4 weeks. MRI shows a heterogeneous midline cerebellar vermis mass causing obstructive hydrocephalus. Histology confirms small round blue cells forming Homer Wright rosettes. Which feature of this tumour dictates that the entire neuraxis must be included in staging and radiotherapy planning?

• A Resistance of the tumour to all chemotherapeutic agents
• B Invariable origin from the vestibular nerve sheath
• C High frequency of leptomeningeal dissemination via cerebrospinal fluid ✓
• D Exclusive growth by local infiltration of the brainstem

Explanation

Medulloblastoma is a primitive neuroectodermal tumour of the cerebellar vermis in children that characteristically seeds the subarachnoid space through CSF, producing drop metastases along the spinal cord. Staging therefore requires whole-neuraxis MRI and CSF cytology, and treatment includes craniospinal irradiation. Local brainstem invasion does occur but is not the reason for neuraxis coverage, and the tumour is chemosensitive, so options B, A and D are incorrect.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.