mercoledì 29 agosto 2007
Repeat selected MR image
Figure 1: Initial CT of the head showed an intraparenchymal bleed in the left frontal subcortical region.
Subsequent MRI showed the bleed to be predominantly isointense on T1-WI (Figure 2) and heterogeneously bright on T2-WI (Figure 3), suggestive of hyperacute to acute stage. Mild perilesional edema is seen with no abnormal adjacent flow voids. Generalized volume loss is also noted. Gradient echo images (Figure 4 and Figure 5) show multiple, patchy areas of hemorrhage in the bilateral superficial, subcortical white matter appearing as areas of susceptibility.
Follow-up MRI shows the intraparenchymal bleed as high-signal on T1-WI (Figure 6) and hyperintense on T2-WI (Figure 7) suggestive of late-subacute nature of bleed.
Diagnosis: Cerebral amyloid disease (angiopathy)
Cerebral amyloid disease is a localized form of amyloidosis characterized by extracellular deposition of ß-amyloid in the brain, and it is not associated with systemic amyloidosis. It is found at autopsy in 33% of 60–70 year olds and the prevalence increases to 75% of people older than 90 years. Cerebral amyloid deposition occurs in three morphologic varieties, with cerebral amyloid angiopathy (CAA) being the most common with deposition of ß-amyloid protein in the media and adventitia of small and medium-sized vessels of the cerebral cortex, subcortex, and leptomeninges. Amyloidoma and diffuse encephalopathic white matter involvement are rare.
Many cases of CAA are asymptomatic. When symptomatic, typical presentations include acute intracranial hemorrhage, symptoms resembling a transient ischemic attack (TIA), or dementia. However, these symptoms are not specific for CAA and are often not readily associated with CAA. With continued aging of the population, CAA will become even more prevalent, making correct characterization of imaging findings important.
The deposition of ß-amyloid in the vessel wall is associated with fibrinoid necrosis, focal vessel wall fragmentation, and microaneurysms, which all predispose the patient to repeated episodes of blood vessel leakage or frank hemorrhage. Luminal narrowing may occur at sites of fibrinoid necrosis, which can lead to ischemic change. Histologically, ß-amyloid deposits stained with Congo red show classic yellow-green birefringence under polarized light.
Nonenhanced head CT is the preferred initial imaging modality as it provides crucial information regarding the characteristics of the intracranial hemorrhage, including size, location, shape, and extension to the extra axial spaces. MRI is best suited for identification of small or chronic cortical hemorrhages and ischemic sequalae of this disease, exclusion of other causes of acute cortical-subcortical hemorrhage, and assessment of disease progression. GRE is currently the most sensitive MR imaging sequence for detection of the chronic cortical-subcortical microhemorrhages. Local magnetic field inhomogeneity related to the presence of hemosiderin causes a marked loss of signal on T2*-weighted GRE imaging.
CAA-related ICH represents only 2% of all ICH but is an important cause of hemorrhage in normotensive elderly patients without trauma, representing 38% to 74% of ICH cases in the elderly. CAA-related ICH exhibits a distinctive cortical-subcortical distribution that generally spares the deep white matter, basal ganglia, and brainstem. Angiography does not play a role in the evaluation of CAA.
CAA should be considered in the broad differential diagnosis of leukoencephalopathy, especially if associated with cortical-subcortical hemorrhage(s) or progressive dementia. In CAA, atrophy is most likely the result of chronic small vessel ischemia related to ß-amyloid deposition and is usually seen in association with leukoencephalopathy.
There is no current treatment to halt or reverse ß-amyloid deposition. Patients with CAA have an increased risk of bleeding while taking warfarin, even when the level of anticoagulation is in the therapeutic range. The risk-benefit ratio of anticoagulation and thrombolytic therapy in CAA patients should be carefully considered on an individual basis.