CT brain has shadows suggesting the presence of hypodensity in that part. CT hypodensity has the following possible diseases: 1, cerebral infarction is the most common brain hypodense foci, which are not obvious within 48 hours after the infarction just occurred, and more than 48 hours will see obvious hypodense shadows. fresh lesions will be surrounded by a more vague edema band, while the edge of old lesions will be sharper. 2, cysts, which are more common Arachnoid cysts, located in the temporal pole or occipital pool, can also be in the pineal gland and other parts of the brain. 3, tumors, such as gliomas or astrocytomas, sometimes accompanied by hemorrhage, will have a mixed high density. 4, brain softening foci, which can be left after surgery, or after traumatic brain injury, brain hemorrhage or cerebral infarction, encephalitis, etc., are not specific. The edges are relatively sharp and clear, and the interior is filled with glial cells.