Claudia Grosse, MD , Alexandra Grosse, MD
Pulmonary hypertension may primarily affect either the arterial (pre¬capillary) or the venous (postcapillary) pulmonary circulation. Pulmo¬nary arterial hypertension may be idiopathic or arise in association with chronic pulmonary thromboembolism; pulmonary embolism caused by tumor cells, parasitic material, or foreign material; parenchymal lung disease; liver disease; vasculitis; human immunodeficiency virus infection; or a left-to-right cardiac shunt. Its histologic characteristics include vascular changes—medial hypertrophy, intimal cellular pro¬liferation, intraluminal thrombosis, and the development of plexiform lesions—that manifest primarily in the muscular pulmonary arteries. Features of pulmonary arterial hypertension that may be seen at com¬puted tomography (CT) are central pulmonary artery dilatation, abrupt narrowing or tapering of peripheral pulmonary vessels, right ventricular hypertrophy, right ventricular and atrial enlargement, dilated bronchial arteries, and a mosaic pattern of attenuation due to variable lung perfu¬sion. Pulmonary venous hypertension may result from pulmonary veno-occlusive disease, pulmonary venous compression by extrinsic lesions (eg, mediastinal fibrosis), left-sided cardiac disease, or pulmonary vein stenosis. Its histologic hallmarks include venous intimal cellular prolifer¬ation, medial hypertrophy, and thickening of the internal elastic lamina; capillary congestion and proliferation; interlobular septal thickening; lymphatic dilatation; and, sometimes, venous infarction and vascular changes characteristic of pulmonary arterial hypertension. CT scans in patients with pulmonary venous hypertension show pulmonary intersti¬tial and alveolar edema with signs of pulmonary arterial hypertension. High-resolution CT with standard axial and angiographic acquisitions is useful for identifying underlying disorders and differentiating among the various causes of secondary pulmonary hypertension.