26 years, Female, new posterior fossa mass. There is an enhancing mass centered on the inferior aspect of the fourth ventricle measuring 2.5 x 2.4 x 4.0 cm in the AP, transverse, and craniocaudal dimensions. The mass is almost entirely solid with small foci of cystic change within the lesion. There appears to be infiltration of the posterior aspect of the medulla. There is mild to moderate degree of enhancement, primarily in its posterior and superior aspects. Mass extends inferiorly through the foramen of Magendie. There is mild prominence of the lateral and third ventricles as well as the cerebral aqueduct suggesting mild ventricular outflow obstruction. There is also anterior displacement of the medulla with effacement of the ventral CSF space at the foramen magnum. There is mild restricted diffusion associated with the mass indicating tumor cellularity. There are also small foci of susceptibility which may represent minimal hemorrhage or mineralization.Remainder of the brain demonstrates no parenchymal signal abnormality. No additional foci of parenchymal or meningeal enhancement. No extra-axial collections. Major flow-voids are preserved. There is mild mucosal thickening involving the right greater than left frontal sinuses and anterior ethmoid air cells. There is diffuse opacification of the bilateral mastoid air cells.
1. Enhancing mass centered on the inferior aspect of the fourth ventricle measuring 2.5 x 2.4 x 4.0 cm. There appears to be infiltration and expansion of the posterior inferior aspect of the medulla suggesting possibility that this mass arises from the posterior medulla with exophytic extension into the fourth ventricle. Differentials include brainstem glioma as well as medulloblastoma and ependymoma.2. Mild enlargement of the more proximal ventricular system related to outflow obstruction.