Medulloblastoma

1-Average age is 7 years.

2-Present in the fourth ventricle region.

3-Arises from the roof of the fourth ventricle resulting that a part of it will be in the fourth ventricle while the other part is in the cerebellum so you can see a part of the fourth ventricle compressed by the tumor.It could be calcify and also shows cystic changes.

4-Evidence of supra tentorial hydrocephalus.

5-In the sagittal image of MRI,you can find a sign which could differentiate medulloblastoma from ependymoma which is in case of ependymoma the tumor is casting inside the ventricle while in case of medulloblastoma the tumor is arising from the cerebellum and encroaching upon the fourth ventricle in addition to another sign which is that in case of ependymoma the lesion tend to extend through ventricular foramina while in case of medulloblastoma is not.

6-It could contains cystic component as ependymoma.

Conclusion:

-When you see a lesion arising from the area of the fourth ventricle
 you must put the following differential diagnosis
-Ependymoma.
-Medulloblastoma.
-Epidermoid cyst.
Look to the contrast study, if the lesion is not enhancing, so it will be a dermoid cyst.
If it is an enhancing lesion, think about ependymoma or medulloblastoma, where you can differentiate by the following:
Ependymoma causes complete disappearance of the fourth ventricle and can extend through the foramina of the fourth ventricle while in case of medulloblastoma you can find a part of the fourth ventricle compressed and it never extend through the foramina.
 In the sagittal image of MRI,you can find a sign which could differentiate medulloblastoma from ependymoma which is in case of ependymoma the tumor is casting inside the ventricle while in case of medulloblastoma the tumor is arising from the cerebellum and encroaching upon the fourth ventricle in addition to another sign which is that in case of ependymoma the lesion tend to extend through ventricular foramina while in case of medulloblastoma is not.