Primitive Neuro-epithelial Tumors(PNET)

1-A rare group of tumors formed of undifferentiated cells.

2-Generally occur in the pediatric age group.

3-Include the following

-Medulloblastoma.

-Retinoblastoma.

-Others.

4-Can not be differentiated radiologically.

5-In the clinical practice, any tumor seen in the region of the fourth ventricle, you must diagnose it as ependymoma or medulloblastoma if it shows contrast enhancement and if it shows no enhancement it could be diagnosed as epidermoid cyst.

6-Could be included in the differential diagnosis of a mid line hyper dense homogeneously enhancing lesion seen in the area of the fourth ventricle.

7-Very rare to be calcified or shows cystic changes or present outside the mid line.

8- If you want to diagnose PNET you must exclude two most important signs to exclude ependymoma which are presence of calcification and cystic changes.