As demonstrated on the preceding CT scan, within the right cerebellopontine angle is a well-circumscribed CSF intensity lesion with bony remodelling of the petrous apex and indentation of the middle cerebellar peduncle. Content follows CSF on all sequences including diffusion-weighted imaging. No abnormal enhancement. The seventh and eighth cranial nerves are displaced anteriorly. The ventricles are unremarkable in appearance with no evidence of a hydrocephalus.
Conclusion: Right cerebellopontine angle arachnoid cyst.