Medulloblastoma (Lateral origin)

A 30 yo female with giddiness.

Findings:
A hyper dense right Cp angle mass with fluid – fluid levels on Non contrast CT.
On  MRI, lesion is iso intense to cortical grey matter on T1 as well as T2 images.
Restricted diffusion on diffusion weighted images.
Faint heterogeneous enhancement on post contrast T1.
Multiple fluid – fluid levels with low signal intensity hemosiderin staining in dependent portions on T2*GRE implies to intra lesional bleed, a faint focus of T1 bright signal in dependent portion of mass attributed to meth Hb – a sub acute stage blood degradation product.
A rim of perilesional edema in adjacent right cerebellar hemisphere.
It is difficult to comment whether lesion is extra axial or intra axial as cerebellum is displaced by mass but there is no clear demarcation between the mass and cerebellum even on post contrast T1.
Single voxel MR Spectroscopy shows significantly reduced NAA at 2ppm, high choline at 3.2ppm  and a lactate peak at 1.3ppm.
Mass effect significant, medulla and Pons compressed. Obstructive hydrocephalus due to fourth ventricle compression evident by mild dilatation of temporal horns of lateral ventricle.

Imagingwise Possible DDs: Medulloblastoma, Meningioma.
Acoustic Schwannoma unlikely as there is no intra canalicular extension or widening of IAC.

Histopathology report : Medulloblastoma – Classic Desmoplastic variant, WHO Grade IV with lateral cerebellar origin – atypical for location. 


Medullobastoma
Syn: MB, Posterior fossa PNET, PNET – MB,
A highly cellular embryonal cell tumor.
Age group : common in children, ~75% diagnosed by 10 years.
3 times more common in males.


Location:
Intraventricular – 4th ventricular roof is a typical and most common location. A most common posterior fossa tumour in children. 
Lateral origin – Cerebellar hemisphere is an atypical location common in older children and adults.

Size vary, average size ranges between 3- 5cm at the time of presentation.
On Non contrast CT, solid 4th ventricle mass, hyperdense, calcifcaiton seen in ~20% cases, small intra tumoural cysts, necrosis in ~50% cases.
On MR signal on T1 iso - hypo intense to cortical grey matter on T1 , iso – hyperintense on T2w and FLAIR. High signal on diffusion attributed to its dense, highly cellular nature.
An associated Obstructive hydrocephalus is common seen in ~ 95% cases.
Usually mild to moderate and homogenous enhancement, may show patchy heterogeneous enhancement due to areas of necrosis.
On MR Spectroscopy, NAA reduced or absent as it’s a non neuronal tumour, raised choline.


Other cases of Medulloblastoma with typical location and drop metastasis.