Case contributed by Assoc Prof Frank Gaillard


Presented with hydrocephalus, and underwent an endosocopic third ventriculostomy at another institution prior to being imaged.

Patient Data

Age: 20 years
Gender: Female

CT Brain


There is 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. Anterior pneumocephalus consistent with recent intervention.


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 right 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, pineal region, third ventricle, quadrigeminal cistern

Thoracic MRI


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

Annotated images

Annotated image

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. 


MICROSCOPIC DESCRIPTION: Paraffin sections show a densely hypercellular tumor involving cerebellum with features of medullablastoma.  Tumor 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.  Tumor predominantly involves cerebellar white matter but focally is seen to stream through cerebellar cortex from a persistent external granular layer. Tumor also extends to overlying leptomeninges. 

Immunohistochemistry shows strong diffuse staining for synaptophysin in tumor cells and focal weak staining for GFAP. This profile is in keeping with medulloblastoma. The topoisomerase labeling 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 favor an ependymoma, whereas the fact that the lesion arises from the vermis and presence of numerous supratentorial deposits favors a medulloblastoma (ependymomas tend to seed inferiorly). 

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