Choroid plexus papilloma

There is a midline extra-axial expansile lesion is presumably in the 4th ventricle measuring 4.8 x 3.7 cm. There is mass effect on cerebellar hemispheres laterally, and medulla and upper spinal cord anteriorly but no hydrocephalus or significant vasogenic edema. There is no considerable enlargement of the foramen of Luschka bilaterally to suggest their involvement. The lesion is heterogeneously hypodense with small calcified foci in the anteroinferior aspect.

There is an expansile T1 hypointense to white matter and T2/FLAIR hyperintense lesion located in the inferior aspect of the cerebellar interhemispheric fissure and floor of the forth ventricle. It is extended to the foramen of magnum, causing mass effect on the medulla and upper spinal cord anteriorly and on the cerebellar hemispheres laterally. The Magendie and Luschka foramina are spared. There is no obstructive hydrocephalus.

The lesion is lobular in appearance and enhances homogeneously with no significant vasogenic edema. There is no restricted diffusion or foci of hemorrhage. There is no dural tail or CSF cleft sign. The remainder of the study is non-significant.

Given the Ct and MRI characteristics of the tumor within the floor of the forth ventricle, the most likely diagnoses include ependymoma and choroid plexus papilloma. Medulloblastoma is less likely as the lesion has no restricted diffusion. 

Case contributed by Dr. Lorne Rosenbloom, neuroradiology assistant professor of McGill University.