How do you differentiate it from an arachnoid cyst?
Epidermoid cysts generally show diffusion restriction.
T1: isointense lesion to CSF in the posterior fossa anteriorly more extending to right side
T2: it is confirmed that the lesion follows CSF in most of the sequences
FLAIR: heterogeneous/dirty signal without associated oedema
DWI/ADC: increased signal intensity on DWI and ADC with values similar to adjacent brain parenchyma, indicating abnormal restricted diffusion; this pattern is not observed in arachnoid cysts
the lesion exerts mass effect upon the brain stem, mainly compressing the pons and brainstem. It is completely encasing basilar artery and its branches. It also extends to right cerebellopontine angle displacing the right VII and VIII nerves posteriorly. It is also indenting the 4th ventricle