A large, lobulated extra-axial mass is evident in the prepontine and interpeduncular cistern, extending through the foramen magnum into the anterior spinal canal up to the inferior aspect of the C2 vertebral body. The mass extends into the middle cranial fossa on the right side via Meckel's cave and into the posterior aspect of the suprasellar cistern on the right side. The mass also extends up to the CP angles bilaterally.
It results in compression of the pons and medulla oblongata and attenuation of the fourth ventricle, but no hydrocephalus. Within the spinal canal, the mass results in spinal cord compression.
The mass encases both vertebral arteries as well as the basilar artery. It causes medial displacement of the right posterior communicating artery.
On T1WI, the mass is hyperintense but is isointense to white matter on T2WI. It is of inhomeogenous signal intensity on FLAIR and does not enhance post contrast. Fluid restriction is demonstrated on diffusion weighted imaging (DWI) and corresponding apparent diffusion coefficient (ADC).