Pathology of pulmonary vasculitis.

There are three major vasculitis syndromes that affect the lung: Wegener's granulomatosis (WG), Churg-Strauss syndrome (CSS), and microscopic polyangiitis (MPA). The pathology of pulmonary vasculitis is complicated because it requires correlation with clinical, laboratory, and radiological features; there is overlap in some histological features among the vasculitis syndromes; biopsies early in the course of disease or after therapy may show atypical or incomplete histological features; the differential diagnosis is complex and includes infection that should not be treated with corticosteriods or immunosupressive agents; and few pathologists have much experience with these cases. Major histological features of necrosis, granulomatous inflammation, and vasculitis characterize WG. The inflammatory consolidation consists of a mixture of neutrophils, lymphocytes, plasma cells, macrophages, giant cells, and eosinophils. Necrosis may take the form of neutrophil microabscesses or geographic necrosis. Granulomas may take several forms, including scattered or loose clusters of giant cells, palisading histiocytes or giant cells lining the border of geographic necrosis or microabscesses, and palisading microgranulomas. Sarcoidal granulomas are very rare. CSS may show eosinophilic pneumonia, allergic granulomas, and eosinophilic vasculitis. Asthmatic bronchitis may also be present. Biopsies from CSS patients are rare because this syndrome is usually diagnosed clinically. Microscopic polyangiitis demonstrates neutrophilic capillaritis and diffuse alveolar hemorrhage.