How do you diagnose a brain infection?

Encephalitis?: Brain abscess, encephalitis, and others can be evaluated using imaging studies like an MRI and others, a lumbar puncture, serologies, but primarily focused around findings on history and physical exam.

CSF tests, imaging: While there are certain blood test results or MRI findings that raise the suspicion for infection, a definitive diagnosis often requires a lumbar puncture for analysis of cerebrospinal fluid. That being said, in many cases we will treat infections empirically just based on clinical suspicion, especially if the patient is presenting with seizures or other worrisome signs.