 The hematoma can exert a mass effect on the brain, increasing intracranial pressure and potentially causing midline shift or deadly brain herniation.In the past this effect held additional diagnostic importance since prior to the invention of modern tomographic soft-tissue imaging utilizing MRI or CT it was not possible to directly image many kinds of primary intracranial lesions.Therefore in those days, the mass effect of these abnormalities on surrounding structures was sometimes used to indirectly infer the existence of the primary abnormalities themselves, for example by using a cerebral angiography to observe the secondary vascular displacement caused by a subdural hematoma pushing on the brain, or by looking for a distortion caused by a tumor on the normal outline of the ventricles as depicted on a pneumoencephalogram.