This is a 62 years old lady with right trigeminal neuralgia and ataxia. Preserved hearing. Most likely diagnosis?
- Acoustic Schwannoma
- Arachnoid Cyst
- Trigeminal Schwannoma
- Epidermoid cyst
Congratulations to those who selected Trigeminal schwannoma. Schwannoma can be purely solid or solid cum cystic. This one is predominantly cystic with some solid part towards the Meckel’s cave which is heterogeneously enhancing on contrast.
It is sparing the 7th nerve on T2 and is not causing dilatation of the internal auditory canal which is the hallmark of Acoustic schwannoma. 9th nerve lesions generally do not extend to the middle cranial fossa and generally remain in the posterior cranial fossa.
Lack of diffusion restriction rules out the Epidermoid cyst. Arachnoid cysts have the same signals as CSF on all sequences including FLAIR. This lesion is hyper-intense on FLAIR.
Metastasis is always a differential in adults with posterior fossa lesions, however, they almost always have significant surrounding edema – not seen on these scans.