Infections can cause vasculitis both by direct invasion of the vessel walls and by an immune-mediated response to the pathogens. Bacterial, fungal and some viral vasculitis (e.g. herpes virus) cause a direct invasion of the vessel walls, usually resulting in infarction (Fig. 7.8) [2, 24]. Vasculitis with aseptic meningitis is probably related to an immunologic re-action,which can show reversible lesions. Aspergillus infiltrates and destroys the internal elastic lamina of major cerebral arteries, which results in infarction, abscess formation and hemorrhage  (Fig.7.9).In-fection of the infarcted tissue may be aggressive, and direct extension into the surrounding brain may progress quickly.
Pneumococcal meningitis and vasculitis in a 4-year-old girl with high fever. a T2-weighted image reveals hyperintense lesions in bilateral basal ganglia (arrows). b DW image shows these lesions as very hyperintense, representing acute or subacute infarcts due to infectious vasculitis (arrows). c ADC demonstrates low signal, confirming acute or subacute infarcts due to infectious vasculitis (arrows).d MRA shows stenosis of internal carotid arteries,right middle cerebral and left anterior cerebral arteries (arrows)
Disseminated aspergillosis in a 48-year-old female presenting with altered mental status and a history of acute lymphoblastic leukemia, post recent bone marrow transplant. a T2-weighted image shows a high signal intensity lesion (arrow) at the corti-comedullary junction in the medial left frontal lobe. A hypointense spot in this lesion represents a hemorrhagic component (arrowhead). b Gadolinium-enhanced Tl-weighted image reveals no enhancement within this lesion (arrows). c DW image shows this lesion containing areas of very high signal intensity (arrows), indicating a vasculitis-mediated acute septic infarction. d ADC shows heterogeneous decreased signal (arrows) in the lesion,confirming a conglomerate of acute septic infarctions. (From )
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