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.

Chronic pulmonary thromboembolism is mainly a consequence of incomplete resolution of pulmonary thromboembolism. Increased vascular resistance due to obstruction of the vascular bed leads to pulmonary hypertension. Chronic thromboembolic pulmonary hypertension is clearly more common than previously was thought, and misdiagnosis is common because patients often present with nonspecific symptoms related to pulmonary hypertension. Computed tomography (CT) is a useful alternative to conventional angiography not only for diagnosing chronic pulmonary thromboembolism but also for determining which cases are treatable with surgery and confirming technical success postoperatively. The vascular CT signs include direct pulmonary artery signs (complete obstruction, partial obstruction, eccentric thrombus, calcified thrombus, bands, webs, poststenotic dilatation), signs related to pulmonary hypertension (enlargement of main pulmonary arteries, atherosclerotic calcification, tortuous vessels, right ventricular enlargement, hypertrophy), and signs of systemic collateral supply (enlargement of bronchial and nonbronchial systemic arteries). The parenchymal signs include scars, a mosaic perfusion pattern, focal ground-glass opacities, and bronchial anomalies. The presence of one or more of these radiologic signs arouses suspicion and allows diagnosis of this entity. Early recognition of chronic pulmonary thromboembolism may help improve the outcome, since the condition is potentially curable with pulmonary thromboendarterectomy.

Thoracic aortic dissection is the most frequent cause of aortic emergency, and unless it is rapidly diagnosed and treated, the result is death. Helical computed tomography (CT) permits the diagnosis of acute aortic dissection with a sensitivity and specificity of nearly 100%. This imaging modality also enables differentiation between proximal aortic dissection (type A in the Stanford classification) and distal aortic dissection (Stanford type B), which are treated differently and have different prognoses. In 70% of patients in whom nontraumatic acute thoracic aortic dissection is diagnosed after evaluation with helical CT, scans show the typical signs of aortic dissection, with rupture and displacement of the intima. CT also can depict other pathologic entities with similar clinical manifestations, such as intramural hematoma and penetrating atherosclerotic ulcer. Awareness of the different radiologic appearances of these disease entities is essential for differential diagnosis. More than one-third of patients with aortic dissection show signs and symptoms indicative of systemic involvement. Because branch-vessel involvement may increase morbidity and mortality, in this group of patients it is important to evaluate the entire aorta so as to determine the distal extent of the dissection and detect any systemic involvement.

Various congenital and acquired anomalies may affect the pulmonary arteries in adult patients. Congenital anomalies (proximal interruption, anomalous origin of the left pulmonary artery [pulmonary artery sling], and idiopathic dilatation of the pulmonary trunk) are usually found incidentally at chest radiography or computed tomography (CT). Acquired anomalies include diffuse or focal enlargement of the arteries because of pulmonary hypertension, aneurysm, and intravascular pulmonary metastasis; decreased arterial diameter because of bronchial carcinoma, mediastinal fibrosis, and Takayasu arteritis; and intraluminal filling defects due to pulmonary thromboembolism and pulmonary artery sarcoma. An awareness of the radiologic manifestations of the disease entities and potential pulmonary artery complications secondary to infection or vasculitis may enable an early diagnosis. CT angiography is becoming the standard method for evaluating patients in whom the presence of pulmonary embolism is suspected. CT assessment of the extent of heart effects in patients with pulmonary hypertension and pulmonary embolism is particularly important because such effects largely determine the prognosis.

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