Medulloblastoma

Case contributed by A.Prof Frank Gaillard

Presentation

This young woman presented with hydrocephalus, and underwent an endosocopic third ventriculostomy at another institution prior to being imaged.

Patient Data

Age: 20
Gender: Female
CT

CT Brain

CT scans demonstrate a large posterior fossa mass, located in the midline, with faint speckled calcification anteriorly. It appears isodense with grey matter.  The 4th ventricle appears displaced anteriorly. 

MRI

MRI confirms a mass arising from or invading the vermis. It is isointense to T1 and hyperintense on T2 with restricted diffusion, consistent with a cellular histology. Only faint contrast enhancement is present. 

The mass appears to extend through the foramen of Luschka. 

A number of similar signal intensity lesions are scattered throughout the rest of the intracranial cavity, including supratentorially: left middle cranial fossa, pinal region, third ventricle, quadrigeminal cistern. 

MRI

Thoracic MRI

A number of lesions are demonstrated, the largest arising from the posterior aspect of the cord, and demonstrating high T2 signal and contrast enhancement. 

Annotated image

Annotated images

Hyperdense mass (blue dotted line) with calcification anteriorly (green arrow) appears to be located in the verims, posterior to the 4th ventricle (yellow arrow). Inferiorly the mass ( * ) fills the 4th ventricle and extends through the foramen of Luschka (red arrow). 

Multiple high T2 signal nodules are seen both supratentorially and along the cord (blue arrows) in keeping with CSF seeding. 

The patient went on to have a craniotomy and excision of the posterior fossa mass. 

Histology

MICROSCOPIC DESCRIPTION: Paraffin sections show a densely hypercellular tumour involving cerebellum with features of medullablastoma.  Tumour cells have small irregularly shaped hyperchromatic nuclei and form well developed Homer Wright type rosettes.  In addition there is a diffuse sheeted arrangement and a desmoplastic pattern is noted focally.  Some pale areas are also seen.  There are frequent mitotic figures and prominent apoptotic activity. A focus of confluent necrosis with dystrophic calcification is also noted.  Tumour predominantly involves cerebellar white matter but focally is seen to stream through cerebellar cortex from a persistent external granular layer. Tumour also extends to overlying leptomeninges. 

Immunohistochemistry shows strong diffuse staining for synaptophysin in tumour cells and focal weak staining for GFAP. This profile is in keeping with medulloblastoma. The topoisomerase labelling index is aprroximately 30%.

FINAL DIAGNOSIS: Medulloblastoma (WHO grade IV).

Case Discussion

This case illustrates the difficulty in being able to arrive at a firm pre-operative diagnosis, when features are a little atypical. In this case the age of the patient and protrusion through the 4th ventricular foramen favour ependymoma, whereas the fact that the lesion arises from the vermis and presence of numerous supratentorial deposits favours a medulloblastoma (ependymomas tend to seed inferiorly). 

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Case information

rID: 13715
Case created: 9th May 2011
Last edited: 2nd Nov 2017
Inclusion in quiz mode: Included

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