Intraventricular Posterior Fossa Tumors

Case A: A noncontrast CT image demonstrates a hyperdense posterior fossa mass lesion centered within the vermis causing effacement and anterior displacement of the fourth ventricle with associated hydrocephalus. On the T2-weighted image, the lesion is isointense to hypointense to brain parenchyma. On postgadolinium images it demonstrates both solid and rim enhancement. On the ADC image, the solid enhancing component demonstrates low diffusivity, suggesting increased cellularity.

Case B: A lobulated mass lesion centered in the right foramen of Luschka is hyperintense on T2-weighted images and demonstrates mild enhancement with a large posterior lateral component with low diffusivity. The mass also extends through the foramen of Magendie, the bilateral foramen of Luschka, cerebellopontine angles, and prepontine cisterns. The left internal auditory canal involvement is best demonstrated on the CISS sequence.

Case C: A predominantly T2 hyperintense lesion centered within the fourth ventricle demonstrates internal microlobulations. It expands the fourth ventricle without surrounding perilesional edema or infiltration. On the postcontrast T1 axial and sagittal images, contrast enhancement is seen.

Case D: A noncontrast CT scan demonstrates a large heterogenous posterior fossa mass that is hyperdense to the brain parenchyma with multiple nonenhancing small cystic components. The ADC dark, more solid enhancing portion reflects hypercellularity.