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Cytotoxic Edema

Figure 6.1 a-f

Acute infarction with hyperacute hemorrhage (oxy-hemoglobin/deoxy-hemoglobin). A 72-year-old woman suffered from a right-sided weakness. MR imaging 30 hours after the onset of symptoms (a-c) showed a lesion in the right basal ganglia (arrow) that is hyperintense on DW (a) and b0 images (b).On the ADC map (c) the lesion is hypointense (arrow), indicating that this is a non-hemorrhagic acute infarction. During the end of the MR scanning, 30.5 hours after the onset of symptoms (d-f), the patient suddenly lost consciousness.The study was repeated, showing the increased size of the basal ganglia lesion.On the DW image (d) there is now a heterogeneous hyperintensity (arrow), consistent with oxy-he-moglobin.The b0 image (e) also shows the lesion as heterogeneous, hyperintense (arrow), supporting oxy-hemoglobin. Note the new regions of hypointensity around the lesion (arrowhead),indicating deoxy-hemoglobin (d-f).The ADC map (f) shows the lesions as heterogeneously hypointense,consistent with oxy-hemoglobin (arrow). However, it is difficult to calculate the ADC due to the presence of paramagnetic deoxy-hemoglobin (arrowhead).

Results of DW imaging of hematomas at this stage have not been well characterized. In our experience, however, a hyperacute intraparenchymal hemorrhage is hyperintense on DW images, with a decreased apparent diffusion coefficient (ADC). This is in accordance with observations of other authors [28, 33]. The possible causes for the decreased ADC are shrinkage of extracellular space due to clot retrac-tion,changes in the concentration of hemoglobin and a high viscosity [13,19,22-24,28,33-35].

Chronic Hemorrhage
Figure 6.2 a-f

Hyperacute and chronic hemorrhage (oxy-hemoglobin/deoxy-hemoglobin, met-hemoglobin and hemosiderin/ferritin). A 40-year-old woman developed an acute left-sided weakness.A non-enhanced CT scan 6 hours after the onset of symptoms (a) shows a hyperdense lesion (arrow) in the right frontoparietal region associated with a small amount of subarachnoid hemorrhage (arrowhead). MR imaging 12 hours after the onset of symptoms (b-h) shows a heterogeneous lesion with areas of central hyperintensity on the T2-weighted image (b) (arrow; oxy-hemoglobin) with a peripheral hypointensity from the susceptibility influence of paramagnetic material (arrowheads; deoxy-hemoglobin). The T1-weighted image (c) shows the lesion as heterogeneous with areas of isointensity (arrow; oxy-hemoglobin) and hypointensity (arrowheads;deoxy-hemoglobin). Both the DW (d) and b0 images (e) show the lesion as heterogeneous with areas of hyperintensity (arrows;oxy-hemoglobin) and hypointensity (arrowheads;deoxy-hemoglobin).The hypointensity is more prominent on these sequences than on the T2-weighted image (b).The ADC map (f) has a similar appearance of a heterogeneous lesion with areas of hypointensity (arrows;oxy-hemoglobin and arrowheads;deoxy-hemoglobin). As usual, when there is a strong susceptibility influence, it is difficult to calculate ADC.

Cytotoxic Edema Intoxication

The coronal GRE image (g) and the GRE-echo-planar image (h) are more sensitive in depicting the susceptibility effect from deoxy-hemoglobin (arrowheads).The diamagnetic oxy-hemoglobin will,as expected,show an isointense signal (ar-row),similar to the other sequences. Four months after the onset of symptoms (i-n), the patient had a new MR examination. On a T2-weighted image (i),the lesion is still heterogeneous, but there are now areas of hyperintensity (extracellular met-hemoglobin; arrow) and hypointensity (arrowheads; hemosiderin/ferritin).The T1-weighted image (j) shows the heterogeneous lesion with areas of hyperintensity (arrow; extracellular met-hemoglobin) and hypointensity (hemosiderin/ferritin).The DW image (k) show the lesion as hypointense overall and the same is seen on the b0 image (l), but this "T2-weighted" image has a small hyperintense zone in the center of the hematoma, probably due to extracellular met-hemoglobin (arrow).The hypointensity (arrowheads) on the b0 image (l) is more pronounced than on the conventional T2-weighted image (i), demonstrating the higher sensitivity to susceptibility with this imaging sequence.The susceptibility effect will make it difficult to calculate ADC accurately, but the ADC map (m) will demonstrate the susceptibility from hemosiderin/ferritin as peripheral hypointense areas (arrowheads). In the center there are hyperintense areas (arrow), probably containing extracellular met-hemoglobin.The hypointensity on the DW image (k) is probably a combined effect of T2 shortening,magnetic susceptibility and increased diffusibility.A marked peripheral hypointensity from hemosiderin/ferritin will also be seen when a GRE technique (n) is used (arrowheads)

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