INTRACEREBRAL HEMORRHAGE

CT Features

br-740.gif

      Together, hypertension, aneurysm, and vascular malformations account for 80% of intracerebral hemorrhages. All cerebral hematomas, whatever the cause, have a similar resolution pattern on CT. The rate of resolution depends on the size of the hematoma, usually within one to six weeks, and they resorb from the outside toward the center. Perihematoma low density appears in 24-48 hours. Rim enhancement appears in one week and persists for six weeks. The end result of a hematoma is decreased parenchymal density, focal atrophy and local ventricular dilatation.

MR Appearance

      Intracerebral hematomas have a very dynamic appearance on MR, changing in signal intensity over time. Acute blood, in the form the oxyhemogloblin, is isointense with the brain parenchyma. Within a few hours, the oxyhemoglobin is converted to deoxyhemoglobin within the hematoma. Deoxyhemoglobin has a predominant effect of shortening T2, resulting in low signal on T2-weighted images. After three to four days, the deoxyhemoglobin is progressively converted to methemoglobin, which is a paramagnetic substance. Although methemoglobin shortens both T1 and T2, the predominant effect is T1 shortening. As a result, at this stage, hematomas are high signal in both T1-and T2-weighted images. Over the next few months, the methemoglobin is slowly broken down into hemichromes which produce only mild T1 shortening. Hematomas at this end stage are slightly high signal on T1-weighted images and remain high signal on the T2-weighted images. Another interesting phenomenon occurs around the periphery of hematomas. Macrophage activity results in degradation of the methemoglobin and conversion of the iron moiety to hemosiderin. Hemosiderin shortens T2 and produces a black ring around the hematoma on T2-weighted images. We have observed this ring as early as nine days after hemorrhage, and the ring becomes thicker over time. The amount of hemosiderin varies from one hematoma to another, and the specific physiologic and chemical factors that influence this are unknown. In small hematomas (less than 1 cm), we have noted low signal intensity from hemosiderin throughout the cavity. The length of time that the hemosiderin will remain in the area of a hematoma is also unknown, but we have observed hemosiderin at the site of a

br-7401.gif

previous hematoma as long as four years following the primary hemorrhage. From this discussion, it is apparent that the specific signal intensities of a hematoma on T1- and T2-weighted images provide a clue as to the age of the hemorrhage. Endnote Endnote


Hypertensive Hemorrhage

      The criteria for hypertensive hemorrhage include a hypertensive patient, 60 years of age or older, and a basal ganglia or thalamic location of the hemorrhage. A CT scan is the procedure of choice for evaluating these patients. Arteriography is necessary only if one of these criteria is missing. Hypertensive hemorrhages are often large and devastating. Since they are deep hemorrhages and near ventricular surfaces, ventricular rupture is common. One-half of hypertensive hemorrhages occur in the putamen; the thalamus in 25%; pons and brainstem, 10%; cerebellum, 10%, and cerebral hemispheres, 5%.  

{To return to cases, use the "Back " button on the Toolbar}