Neurosurgery

is very high signal on both T1- and T2-weighted images. Throughout these stages there will be an admixture of products present. In large hematomas, the center will be hypoxic, delaying hemoglobin desaturation. High signal occurs from the outside of the hematoma and progresses inwards with time (Fig. 2.5a, b).

Chronic Stage

Edema and mass effect will disappear and the end-stage products of ferritin and hemosiderin form, which are very low on T2 weighting, particularly GE T2. Macrophages laden with these iron storage products will remain for years in the wall of the old hematoma.

Extra-axial Hemorrhage

Acute subarachnoid hemorrhage can be impossible to differentiate from normal CSF on MRI, and CT remains the imaging modality of choice, particularly if the hematoma is only small and not focal. Sensitivity of MRI can be improved by use of FLAIR sequence, particularly if the diagnosis has been delayed, when the CT scan is more likely to be negative. An MR angiogram can be performed whilst the patient is in the scanner.

Extradural and subdural hematomas are very well demonstrated on MRI. Small collections over the surface of the brain and tentorium will be better demonstrated in the coronal plane. The evolving hematoma signal patterns are similar to those of parenchymal hematomas except in the chronic stages, as hemosiderin is not stored. The collection becomes similar to CSF on routine T1 and T2 weighting but remains high signal on proton-density and

Table 2.3. Evolution of hematoma

Phase

Time

Hb Product

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