The most common acute brain diseases include disorders of cerebral circulation (by ischemic and hemorrhagic type), brain tumors (including those with hemorrhage), and inflammatory diseases. Localization of the ischemic zone corresponds to a specific vascular region. Hypodensity often has the form of a wedge. Cytotoxic edema captures white and gray matter. There is a positive dynamics of the development of the pathological process. Contrast agents are used for differential diagnostics with volumetric processes. The accumulation of contrast agent occurs mainly in the course of the brain gyrus. The causes of hemorrhage (non-traumatic hematoma) in the brain can be a hypertensive crisis, aneurysm rupture, hemorrhagic transformation of an ischemic stroke, and a brain tumor. As a rule, differential diagnosis of ischemic stroke has to be performed with astrocytic brain tumors. Also, ischemic stroke should be differentiated from such inflammatory diseases of the brain as encephalitis and vasculitis. Thus, in terms of admissions, multidisciplinary medical institutions have to deal with a variety of acute brain diseases, tomography picture which can be similar and different tomographic manifestations ("masks") of the same pathological processes that requires a mandatory comparison of CT - and MRI-semiotics of these pathological processes with a history and clinical disease.