Intracranial hemorrhage: principles of CT and MRI interpretation

Abstract

Accurate diagnosis of intracranial hemorrhage represents a frequent challenge for the practicing radiologist. The purpose of this article is to provide the reader with a synoptic overview of the imaging characteristics of intracranial hemorrhage, using text, tables, and figures to illustrate time-dependent changes. We examine the underlying physical, biological, and biochemical factors of evolving hematoma and correlate them with the aspect on cross-sectional imaging techniques. On CT scanning, the appearance of intracranial blood is determined by density changes which occur over time, reflecting clot formation, clot retraction, clot lysis and, eventually, tissue loss. However, MRI has become the technique of choice for assessing the age of an intracranial hemorrhage. On MRI the signal intensity of intracranial hemorrhage is much more complex and is influenced by multiple variables including: (a) age, location, and size of the lesion; (b) technical factors (e.g., sequence type and parameters, field strength); and (c) biological factors (e.g., pO2, arterial vs. venous origin, tissue pH, protein concentration, presence of a blood-brain barrier, condition of the patient). We discuss the intrinsic magnetic properties of sequential hemoglobin degradation products. The differences in evolution between extra- and intracerebral hemorrhages are addressed and illustrated.

Comparison of O-(2-18F-Fluoroethyl)-l-Tyrosine and l-3H-Methionine Uptake in Cerebral Hematomas

“…Time course of 3 H-MET uptake is similar to that of 18 F-FET, but after 3-4 wk there was still borderline uptake in some animals. *P , 0.05. findings (24,25). PET using radiolabeled amino acids is helpful in the diagnostic work-up of cerebral gliomas, and 18 F-FET PET may be considered as an additional diagnostic tool when the differentiation of a neoplastic from a nonneoplastic origin of a hematoma is unclear.…”

Blend Sign on Computed Tomography

“…The CT attenuation of blood is dependent on the time course of the bleeding. 19 The density of hematoma is affected by the individual components of the hematoma. The hemoglobin is the most important factor determining CT attenuation of the hematoma.…”

Substantial Observer Variability in the Differentiation Between Primary Intracerebral Hemorrhage and Hemorrhagic Transformation of Infarction on CT Brain Imaging

“…Because the rate of HTI is relatively low within the first 24 hours after stroke onset, 9,10 hematoma density in ICH decreases with time, 11 and because we expected greater radiological agreement in those cases with severe strokes due to large-volume intracerebral hematomas who are more likely to present early and be scanned immediately, we stratified the analysis according to whether or not the scan was performed Ͻ24 of stroke onset. Observer agreement was measured using unweighted statistics.…”

“…The clot retracts; a surrounding hypointense zone due to reactive vasogenic edema appears, and this might be mistaken for underlying infarction. With proteolysis and absorption of globin molecules, the hematoma density also decreases 11 and in turn begins to resemble extravasated blood from vessels damaged by ischemia. Hemorrhages in lobar locations might have been more variably diagnosed because the vascular topography of superficial brain regions is relatively heterogenous, 20 occasionally making it difficult to determine when a hematoma definitely falls outside an arterial territory and is therefore less likely to be a secondary bleed into an infarct.…”

“…However, most clinicians would be reluctant to use these therapies after ICH unless the risk of thromboembolism was also high given that the risk of recurrent hemorrhage outweighs the risk of a future ischemic stroke. 7 Because the incidence of HTI is low within the first 24 hours after stroke onset but increases thereafter, 8 -10 and because ICH may come to resemble HTI as hematoma density decreases with time, 11 delays in brain imaging are likely to make the distinction between ICH and HTI more difficult. Yet, despite efforts to minimize scan delays for patients who are thrombolysis candidates, other patients with minor stroke symptoms, elderly patients, or those who have presented outside the therapeutic time window for thrombolysis are still likely to face scan delays.…”