When to suspect pulmonary vasculitis: radiologic and clinical clues.

Vasculitis is an inflammatory destructive process affecting blood vessels. Pulmonary vasculitis may be secondary to other conditions or constitute a primary, and in most cases idiopathic, disorder. Underlying conditions in the secondary vasculitides are infectious diseases, connective tissue diseases, malignancies, and hypersensitivity disorders. The most widely used approach to classifying the primary vasculitides is based on the size of the affected vessels (large, medium, small). Thoracic involvement is most commonly seen with primary idiopathic large-vessel vasculitides (Takayasu arteritis, giant cell arteritis, Behçet disease) and primary small-vessel antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides (Wegener granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome). The radiologic manifestations of primary pulmonary vasculitis are extremely variable and include vessel wall thickening, nodular or cavitary lesions, ground-glass opacities, and consolidations. Diffuse alveolar hemorrhage is a clinical syndrome that usually results from primary small-vessel vasculitis in the lungs. Although chest radiography is often the first imaging study performed in patients with pulmonary involvement by vasculitis, chest radiographs often fail to show the exact pattern and extent of thoracic involvement and CT is more useful in assessment of the thoracic findings. The pulmonary primary vasculitides are rare disorders, and their diagnoses are among the most demanding challenges in medicine because their signs and symptoms are nonspecific and overlap with those of infections, connective tissue diseases, and malignancies; thus, diagnosis of vasculitis relies on recognition of characteristic combinations of particular clinical, radiologic, laboratory, and histopathologic features.