脑淀粉样血管病 Cerebral Amyloid Angiopathy
脑淀粉样血管病：CT和MR影像学表现 Cerebral Amyloid Angiopathy: CT and MR Imaging Findings
脑淀粉样血管病(cerebral amyloid angiopathy，CAA)是以软脑膜和皮质中、小动脉中膜和外膜出现β-淀粉样蛋白(β-amyloid peptide，Aβ)沉积为特征的一种脑血管病变。散发性CAA通常见于60岁以上的老年人，其发病率随着年龄的增长而升高，65～74岁为2．3％，80岁以上为100％。由于70％～97.6％的阿尔茨海默病(Alzheimer's disease，AD)患者存在CAA，因此被认为是AD的形态学标志，但也可见于无临床症状的健康老年人。多数CAA患者临床表现为痴呆、脑出血或短暂性脑缺血发作，其中脑出血是CAA最常见的临床表现。
The Boston Criteria for Diagnosis of CAA
Figure 1. Histologic appearance of β-amyloid deposition in cerebral cortical vessels. (a) Photomicrograph (original magnification, ×100; Congo red stain) shows highlighted β-amyloid deposits along the vessel walls. (b) Photomicrograph (original magnification, ×100; Congo red stain) obtained with polarized light shows the classic yellow-green birefringence of the β-amyloid deposits.
Figure 2. Determination of ICH location in a 74-year-old man with acute onset of expressive aphasia, confusion, and a right-sided facial droop. Axial nonen-hanced CT scan shows a left-sided frontal cortical ICH, a finding most consistent with CAA-related ICH. Pathologic tissue obtained at hematoma evacuation was positive for CAA. The location of an ICH is helpful in determining the cause of the ICH in a patient with a sudden neurologic deficit.
Figure 3. Sensitivity of GRE imaging for hemosiderin in an 80-year-old man with dementia that has progressed over the past 4 years. (a) Axial GRE MR image shows multiple foci of signal loss in cortical-subcortical locations. In a patient with a diagnosis of probable CAA, these foci are consistent with chronic microhemorrhages. (b) Axial T2-weighted fast spin-echo MR image does not show the foci of chronic microhemorrhage.
Figure 4. Recurrent CAA-related ICH in a 65-year-old woman with progressive aphasia, right visual field deficits, and headache. (a) Axial nonenhanced scan from the initial CT study shows a discrete, ovoid, left-sided occipital ICH. (b) Axial GRE MR image obtained the same day shows numerous cortical-subcortical microhemorrhages, a finding most compatible with a diagnosis of probable CAA. One month later, the patient returned to the emergency department with an increasing level of confusion. (c) Axial nonenhanced CT scan obtained at that time shows a larger, more devastating, left-sided parieto-occipital hemorrhage. Owing to the presence of multiple cortical-subcortical microhemorrhages, which are highly suggestive of CAA, the larger ICH was thought to represent recurrent hemorrhage rather than a hemorrhagic infarction. The patient was not a surgical candidate and was discharged to a hospice 1 week later, where she died after a few days.
Figure 5. CAA-related macrohemorrhage with associated subarachnoid hemorrhage in an 81-year-old man with acute dysphasia and agitation. Axial nonenhanced CT scan shows an irregular, 4 × 5-cm, left-sided frontoparietal cortical ICH. The high attenuation in adjacent sulci (arrowheads) is consistent with subarachnoid hemorrhage. The patient had a diagnosis of probable CAA on the basis of a history of two spontaneous right-sided frontal ICHs.
Figure 6. CAA-related macrohemorrhage with associated subdural hemorrhage in a 77-year-old man with severe headache and difficulty walking. Axial nonenhanced CT scan shows a large right-sided posterior parietal ICH with irregular borders in a cortical location. There is a small right-sided posterior parafalcine subdural hemorrhage (arrow). The large hematoma causes marked effacement of right cerebral sulci and approximately 9 mm of subfalcine herniation. The patient underwent emergency hematoma evacuation; CAA was demonstrated at histologic analysis.
Figure 7. CAA-related macrohemorrhage with associated intraventricular hemorrhage in an obtunded 81-year-old man. (a) Sagittal nonenhanced T1-weighted MR image shows a large frontal cortical ICH. (b) Axial GRE MR image shows that the right-sided frontal cortical ICH extends to the right lateral ventricle. GRE images also revealed multiple cortical-subcortical microhemorrhages, a finding most consistent with a diagnosis of probable CAA. (c) Axial fluid-attenuated inversion-recovery (FLAIR) MR image shows the more rarely associated intraventricular hemorrhage (arrows) as well as subarachnoid hemorrhage (arrowhead).
Figure 8. CAA-related microhemorrhage in a 76-year-old woman with memory loss, seizures, and headaches. CAA was diagnosed with biopsy at another institution. Axial GRE MR image shows multiple cortical-subcortical microhemorrhages, a finding consistent with CAA.
Figure 9. Leukoencephalopathy in a 79-year-old woman with slowly progressive dementia similar to Alzheimer dementia. (a, b) Axial nonenhanced CT scan(a) and FLAIR MR image (b) show symmetric periventricular leukoencephalopathy with sparing of the U fibers, corpus callosum, and internal capsules. The FLAIR image also shows encephalomalacia and hemosiderin from prior macrohemorrhage in the left frontal lobe. (c) Axial GRE MR image shows multiple bilateral cortical foci of hemosiderin, thus increasing the specificity for a diagnosis of probable CAA. The encephalomalacia and hemosiderin in the left frontal lobe are also seen.
Figure 10c. Leukoencephalopathy in a 61-year-old woman with rapidly progressive cognitive decline. (a) Axial FLAIR MR image shows asymmetric lobar leukoencephalopathy extending to involve the U fibers and exerting mass effect on the adjacent sulci, most prominently in the posterior left parietal lobe. The absence of signal abnormality at diffusion-weighted MR imaging made an ischemic process or acute infarction unlikely. CAA was diagnosed with biopsy. (b)Axial GRE MR image obtained after biopsy shows a few cortical microhemorrhages (arrows). The patient was treated with a short course of prednisone taper therapy, which started at 40 mg and produced clinical improvement. (c) Follow-up axial FLAIR MR image obtained 1 year later shows near-complete resolution of the leukoencephalopathy. CAA patients with subacute cognitive decline and leukoencephalopathy may respond to immunosuppressive therapy.
Figure 11. Probable CAA in a 72-year-old woman with speech difficulties and waxing and waning memory loss. (a) Axial FLAIR MR image shows nonspecific atrophy as well as periventricular leukoencephalopathy and prominent left-sided parieto-occipital leukoencephalopathy. (b) Axial GRE MR image shows cortical-subcortical microhemorrhages and a small left-sided parietal cortical-subcortical macrohemorrhage. These findings increase suspicion for probable CAA.
Figure 12. Hypertension-related macrohemorrhage in an 80-year-old woman with right-sided weakness and a blood pressure of 160/85 mm Hg. Axial nonenhanced CT scan shows an area of increased attenuation in the left thalamus, a finding most consistent with an acute hypertensive ICH.
Figure 13. Hypertension-related microhemorrhages in a 91-year-old woman with hypertension and unsteadiness. Axial GRE MR image shows multiple small foci of hemosiderin in both basal ganglia and thalami, locations more consistent with a hypertensive cause.
Figure 14. Large macrohemorrhage in a 66-year-old man with biopsyproved brain metastases from small cell lung cancer who presented with headache, light-headedness, and difficulty walking. (a) Axial FLAIR MR image shows a large right-sided frontal cortical hematoma with surrounding vasogenic edema. A fluid-fluid level is present, as is often seen in patients undergoing anticoagulation therapy. This patient was taking clopidogrel for a coronary stent. (b) Axial contrast-enhanced T1-weighted MR image shows a second, nonhemorrhagic metastatic lesion in the right temporal lobe (arrow).