Many I think. Illness caused by an infectious organism such as a virus or bacterium for e.g. meningitis, encephalitis, toxoplasmosis, subdural empyema, etc.

You can check this articles:

https://www.msdmanuals.com/home/brain,-spinal-cord,-and-nerve-disorders/brain-infections/overview-of-brain-infections

https://www.webmd.com/brain/brain-swelling-brain-edema-intracranial-pressure#1

Also, if you want, you can edit your question and add additional topics, not only "brain", for e.g. "neurology", "neurosurgery", "medicine", etc.