RADIOLOGY: HEAD: Case# 33610: CHOROID PLEXUS PAPILLOMA (CPP). This 9 month old child presented with a history of lethargy. T1 weighted axial MRI reveals an intermediate signal mass in the lateral ventricle. T1 weighted axial MRI after gadolinium shows intense, homogeneous enhancement of the mass in the lateral ventricle. T2 weighted axial MRI shows intense surrounding vasogenic edema. Choroid plexus papilloma (CPP) are the most common tumor arising in the trigone of the lateral ventricle in children. They represent 2-5% of all primary brain tumors in children, with almost 90% occurring in children less than five years old. In children, they usually arise in the trigone of the lateral ventricle. In adults they commonly arise in the fourth ventricle. Less than 10% occur in the third ventricle or elsewhere. Patients usually present with hydrocephalus. CPPs typically enhance dramatically following contrast administration on CT or MRI. Parenchymal invasion with edema may occur. Imaging findings are not reliable for distinguishing between CPP and choroid plexus carcinoma, which represent about 10% of choroid plexus neoplasms.