It can detect oedema, hydrocephalus, shift, or imminent ventricular rupture. A brain abscess appears as a hypodense centre with an outlying uniform ring of enhancement, surrounded by a variable hypodense region of brain oedema. Contrast enhancement is essential. Although CT is very sensitive for detecting brain abscess, the findings are not specific, particularly in early disease. It appears to be more sensitive for detecting cerebral oedema and early changes associated with brain abscess.
Gadolinium enhancement provides additional information about brain abscess structure.
The important distinction when treating focal CNS lesions is whether the patient has cerebritis or a brain abscess. Cerebritis is an area of low density on imaging studies surrounded by ring enhancement that does not decay on contrasted scans 60 minutes later. This difference is important, because cerebritis can be cured with antibiotics alone, without the subsequent development of an abscess. There were 67 cases of brain abscess reportedly cured by medical therapy alone from 1975 to 1985. The initial diagnosis and resolution of the abscess were documented by CT, patients were treated with parenteral antibiotics for more than 8 weeks, and there was lack of surgical or histopathologic evidence of encapsulation.