A CSF density lesion in the right cerebellopontine angle, with moderate local mass effect with mild displacement of the brainstem but no effacement of the fourth ventricle. No widening of the adjacent porus acousticus. Remodelling of the adjacent bone is, however, present.
Conclusion: Right cerebellopontine angle cystic lesion most likely represents an incidental arachnoid cyst with a differential diagnosis that includes epidermoid cyst or cystic acoustic neuroma (the latter two are thought less likely).