In the early stage of the subacute hematoma (Figs. 6.2 and 6.3), there is a decline in the energy state of the red blood cell and hemoglobin is oxidized to met-he-moglobin [3,4,7,10,11,14,19,22,23,28-30, 33, 34]. In met-hemoglobin the iron is still bound to the heme moiety within the globin protein, but it is now in the ferric state with five unpaired electrons. This transformation normally starts in the periphery of the hemorrhage and gradually evolves to the center. In the transition to met-hemoglobin, conformational changes will take place in the molecule and water protons will now have access to the unpaired electrons of iron in met-hemoglobin, creating a proton-electron, dipole-dipole interaction. Dipolar relaxation enhancement will then take place, making met-hemoglobin appear hyperintense on T1-weight-ed images. Met-hemoglobin, as a paramagnetic sub stance, will induce magnetic susceptibility relaxation affecting the transverse relaxation (T2* effect), which results in a marked hypointensity on T2-weighted images [3,6,7,10,14,22-24,28-31,33,34].
On DW imaging, intracellular met-hemoglobin shows hypointensity due to these paramagnetic susceptibility effects and ADC measurements are not reliable due to the susceptibility effects [28-30,33].
Figure 6.3 a-e
Acute to early subacute hemorrhage (deoxy-hemoglobin and intracellular met-hemoglobin). A 49-year-old man with headache and aphasia was referred for MR imaging 24 hours after the onset of symptoms (a-e).This study shows a left temporal lobe lesion that is hypointense on the T2-weighted image (a) (arrow; deoxy-hemoglobin and intracellular met-hemoglobin) with surrounding edema. On the Tl-weighted image (b) the lesion is heterogeneous with areas of hypointensity (arrow;deoxyhemoglobin) and hyperintensity (arrowhead;intracellular met-hemoglobin).The DW image (c) demonstrates hypointensity (arrow; deoxy-hemoglobin and intracellular met-hemoglobin). The surrounding hyperintense rim (arrowhead) is a magnetic susceptibility artifact.This peripheral artifact is also seen around the hypointensity (arrow) created by deoxy-hemoglobin and intracellular met-hemoglobin on the b0 image (d). ADC cannot be calculated accurately, which is easy to understand when looking at the extremely heterogeneous lesion depicted on the ADC map (e)
Late subacute-chronic hemorrhage (extracellular met-hemoglobin and hemosiderin/ferritin). A 52-year-old man with a history of chronic hypertension complained of headache and aphasia.MR examination 2 months after the onset of symptoms shows a left temporal lobe lesion that is hyperintense on the T2-weighted image (a) (arrow; extracellular met-he-moglobin) and surrounded by a hypointense rim (arrowheads; hemosiderin/ferritin). Another hypointense lesion is visualized in the right basal ganglia (small arrowhead; hemosiderin/ferritin),compatible with chronic hemorrhage secondary to hypertension.The T1-weighted image (b) shows the temporal lobe lesion as hyperintense (arrow;extracellular met-he-moglobin).The lesion in the right basal ganglia is also hypointense on this sequence (smallarrowhead; hemosiderin/ferritin). On the DW image (c) the temporal lobe lesion is hyperintense (arrow; extracellular met-hemoglobin) with a hypointense rim (arrowheads; hemosiderin/ferritin).The basal ganglia lesion remains hypointense, but the signal void is more extensive than on the conventional T2-weighted image (a), since GRE does not compensate for signal loss due to local magnetic field inhomogeneities and is thus more sensitive than regular spin-echo imaging.This increased susceptibility sensitivity revealed a second,old hemorrhagic lesion in the left thalamus (small arrowhead; hemosiderin/ferritin). The b0 image (d) also shows the hyperintense lesion (arrow; extracellular met-hemoglobin) with the hypointense rim (arrowheads; hemosiderin/ferritin) as well as the older lesions in the basal ganglia and thalamus (small arrowheads; hemo-siderin/ferritin).On the ADC map (e) the temporal lesion is somewhat hypointense (arrow;extracellular met-hemoglobin) with a hypointense rim (arrowheads; hemosiderin/ferritin).The other lesions are also visualized (small arrowheads); however, ADC cannot be calculated. Finally, the coronal GRE image (f) shows the temporal lesion as hyperintense (arrow;ex-tracellular met-hemoglobin) with a hypointense rim (arrowhead; hemosiderin/ferritin).The GRE sequence is the most sensitive and shows multiple small hypointense lesions (old hemorrhagic breakdown products) in the cerebral hemispheres and in the pons (smallarrowheads; hemosiderin/ferritin)
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