What are the key imaging characteristics of brainstem gliomas in the posterior fossa of children, and how do they typically present on MRI and CT scans?

Brainstem gliomas in children are typically located within the brainstem and present as an expansile mass. On CT, they appear isodense to hypodense, while on MRI, they are hypointense on T1-weighted images and hyperintense on T2-weighted images. Key diagnostic features include diffuse infiltration of the brainstem without a distinct mass, often with minimal enhancement after contrast. Clinically, they may present with cranial nerve deficits or long tract signs. A common pitfall is mistaking them for demyelinating lesions or other posterior fossa tumors like medulloblastomas, which have different imaging characteristics.