Cerebritis

1-Caused by infection of the brain tissue by bacteria.

2-Radiologically, it differs completely from that occurs due to viral infection. 

If the patient got cerebritis you will see the following:

-Early you will see bilateral areas of hypo density in the brain tissue then followed by formation of brain abscess.

-Cerebritis cause gyral enhancement after contrast injection which could be seen also in infarction and tumors, you can differentiate between them by clinical history.

-Abscess:

*CT: Hypo dense area rounded or oval affecting brain parenchyma surrounded by edema.

*MRI T1: Hyper intense rounded area surrounded by a hypo intense wall which is also surrounded by hyper intense edema.

*With contrast, it will shows first thin and regular enhancement of the wall and finally it becomes  thick but also regular which can differentiate it clearly from gliomas and other causes leading to marginal enhancement, if the picture is not clear, go immediately to diffusion to solve this problem.

*Diffusion MRI: Restricted diffusion lesion (hyper intense) which must be differentiated from infarction and high cellularity brain neoplasm.

D.D.by clinical history and by ADC map where in case of tumor, it will be hyper intense while in case of infection and infarction, it will be hypo intense.

*Presence of air inside the brain abscess is an indication that it is iatrogenic rather than air forming organisms.

*It causes daughter abscesses, meningitis or ventriculitis.

3-Route of infection:

-Hematogenous.

-From a septic focus, the most common cause of abscess in the cerebellum is septic focus in the ear.

-Penetrating trauma.

-Congenital heart disease due to producing septic emboli directed to the brain.