ARRS Case of the Week
CARDIOVASCULAR IMAGING: Thoracic Arteries
Case Author: Diana Litmanovich, MD, Beth Israel Deaconness Medical Center
56-year-old woman with shortness of breath and known coagulopathy.
Axial (A) and coronal reformatted (B) contrast-enhanced MDCT images of the chest show a linear filling defect in the right lower lobe pulmonary artery. Correlating lung window CT image at the level of the carina (C) shows an area of decreased perfusion in the right lower lobe and dilatation of the main pulmonary artery compared with the aorta.
Chronic pulmonary thromboembolism
Chronic pulmonary thromboembolism is caused by intimal hyperplasia in reaction to pulmonary thrombus, developing in a minority of patients with pulmonary embolism. It is often first identified during the diagnostic workup of unexplained pulmonary hypertension. CT angiography of these patients should be timed in relation to the IV contrast bolus so that both the pulmonary arteries and the aorta are well opacified for optimal imaging of both the pulmonary arteries and bronchial arterial collaterals.
Direct pulmonary arterial signs of chronic pulmonary thromboembolism are related to sequelae of thrombus organization and consist of complete obstruction, eccentric thrombi, beading of the vessel, intimal irregularities, and intravascular bands and webs. Poststenotic dilatation and aneurysm of the pulmonary arteries are common.
An intravascular band is a linear structure attached to both ends of the vessel wall with a free unattached midportion. It is usually 0.3–2 cm long and is oriented in the direction of blood flow, along the long axis of the vessel. A web consists of multiple bands with branching, forming a network. Bands and webs are most frequently found in lobar or segmental arteries and rarely are seen in the main pulmonary artery.
Pulmonary hypertension develops as the result of a sustained increase in vascular resistance. The CT findings are enlarged central pulmonary arteries, right ventricular hypertrophy, and right atrial enlargement with a patent foramen ovale. The chronic hypoxemia that accompanies the decreased pulmonary flow causes hypertrophy of the bronchial arteries, providing collateral arterial flow to the lungs.
Parenchymal signs of chronic pulmonary thromboembolism include peripheral scars, focal groundglass opacities, bronchial dilatation, and mosaic perfusion. Mosaic perfusion consists of patchy areas of hypoperfusion distal to occluded vessels and distal to vasculopathy in nonoccluded areas interspersed with areas of increased attenuation related to redistribution of blood flow in the patent arterial bed.
The location and extent of proximal thromboembolic obstruction are the most critical determinants of operability. Placement of a filter in the inferior vena cava is recommended before surgery, except in patients with a clearly defined source of emboli other than the deep veins of the legs. Pulmonary thromboendarterectomy is the treatment of choice with lifelong anticoagulant therapy to prevent recurrent thrombosis.
Castañer E, Gallardo X, Ballesteros E, et al. CT diagnosis of chronic pulmonary thromboembolism. RadioGraphics 2009; 29:31–50
Grosse C, Grosse A. CT findings in diseases associated with pulmonary hypertension: a current review. RadioGraphics 2010; 30:1753–1777
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