(Radiographics. 2002;22:739-764.)
© RSNA, 2002
High-Resolution CT and CT Angiography of Peripheral Pulmonary Vascular Disorders1
Christoph Engelke, MD,
Cornelia Schaefer-Prokop, MD,
Eckart Schirg, MD,
Joachim Freihorst, MD,
Sisa Grubnic, FRCR and
Mathias Prokop, MD
1 From the Department of Radiology, St George’s Hospital, London, England (C.E., S.G.); the Departments of Diagnostic Radiology (E.S.) and Pediatrics (J.F.), Hanover Medical School, Hanover, Germany; and the Department of Radiology, General Hospital Vienna, University of Vienna, Austria (C.S.P., M.P.). Presented as an education exhibit at the 2000 RSNA scientific assembly. Received November 27, 2001; revision requested January 14, 2002 and received February 19; accepted February 22. Address correspondence to C.E., Department of Radiology, Technische Universität München, Klinikum rechts der Isar Ismaninger Strasse 22, 81675 Munich, Germany (e-mail: cengelke@hotmail.com).
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Abstract
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Peripheral pulmonary vascular disorders that can be evaluated with computed tomography (CT) include various disease entities with overlapping imaging features and a wide range of clinical manifestations. The overall accuracy of CT in the diagnosis of pulmonary vascular disorders increases with improved spatial resolution, administration of a high-flow contrast material bolus, and the use of cardiac gating. The integration of high-resolution CT and CT angiographic techniques into one scanning protocol has important clinical implications for multisection CT and makes it the imaging modality of choice in the evaluation of this complex group of disorders.
© RSNA, 2002
Index Terms: Lung, CT, 60.12116, 60.12118 • Lung, diseases, 60.281, 60.60, 60.72, 60.91 • Lung, ground-glass opacification • Lung, hemorrhage Lung, interstitial disease, 60.917 • Lung, nodule, 60.281 • Lung, vascular disease • Pulmonary angiography, 60.12116
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LEARNING OBJECTIVES FOR TEST 1
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After reading this article and taking the test, the reader will be able to:
- Describe high-resolution CT and CT angiographic findings in peripheral pulmonary vascular disorders.
- Demonstrate integrated high-resolution CT and CT angiographic techniques for investigating pulmonary vascular and parenchymal abnormalities.
- Identify specific peripheral pulmonary vascular disorders on the basis of combined clinical and radiologic findings.
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Introduction
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The peripheral pulmonary vasculature can be affected by various disease entities with overlapping radiologic features and a wide spectrum of clinical manifestations. Multisection computed tomography (CT), high-resolution CT, and CT angiography are helpful in evaluating these disease entities.
In this article, we describe high-resolution CT and CT angiographic technique and related artifacts. We also discuss and illustrate the CT morphologic features of all main groups of peripheral pulmonary vascular disorders in relation to their clinical settings. These disorders are illustrated with use of single or multisection CT with multiplanar and three-dimensional postprocessing techniques such as sliding thin-slab maximum intensity projection (MIP) to elucidate their vascular nature. All diagnoses were confirmed histologically if CT findings were nonspecific.
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Examination Technique
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High-Resolution CT
Standard high-resolution CT technique (1-mm collimation, 10-mm intersection gap, high-resolution reconstruction kernel) is sufficient for evaluating changes in the lung parenchyma associated with peripheral pulmonary vascular disorders. Additional expiratory scans are required to distinguish between air trapping and other causes of altered lung attenuation. Scans obtained with the patient in the prone position allow differentiation of hypostasis in the dependent portions of the lungs from true pathologic tissue.
CT Angiography
CT angiography performed with standard parameters on a 1-second single-section helical CT scanner is capable of displaying the central, segmental, and some of the subsegmental pulmonary arteries. A section collimation of 3 mm, a table feed of 5 mm per rotation, and a reconstruction increment of 1–2 mm are generally used. The scanning range is from the dome of the diaphragm to just above the level of the aortic arch (approximately 12 cm).
Better spatial resolution is obtained with a subsecond single-section helical CT scanner and reduced collimation (usually 2-mm collimation and a table feed of 4 mm per rotation). A collimation of 1 mm is possible with 0.75-second scanners with a table feed of 3 mm per rotation. With this protocol, the central pulmonary arterial system from the dome of the diaphragm to the aortic arch can be covered in 30 seconds. The pitch of 3 exceeds the generally recommended limit of 2. However, the longitudinal resolution of 1.7 mm full width at half maximum (FWHM) is substantially better than with collimations of 2 or 3 mm (FWHM = 2.6 mm and 3.6 mm, respectively) (1,2). Subsegmental 5th- and 6th-order arteries can be visualized to good advantage. In addition, reconstruction of axial high-resolution CT scans is possible with high-resolution filter kernels.
Multisection CT allows CT angiography with very high spatial resolution. For multisection CT in a cooperative patient who can sustain a 20–30-second breath hold, a collimation of 4 x 1 mm or 4 x 1.25 mm is used, with a pitch of 6–7. Images with an effective section width of 1.25–1.6 mm are reconstructed every 0.7–1 mm. Depending on the rotation speed of the scanner, the table speed varies between 9.375 mm/sec (0.8-second rotation, pitch of 6) and 14 mm/sec (0.5-second rotation, pitch of 7). With this examination protocol, the whole lung can be covered in 20–30 seconds, yielding nearly isotropic data sets for subsequent reconstruction of arbitrary cut planes with multiplanar reformatting and various three-dimensional rendering techniques. With multisection CT angiography, the demonstration of subsubsegmental 6th-order vessels is excellent. Such scanning protocols allow reconstruction of high-resolution CT scans at any position and spatial orientation within the data volume (3,4). If the patient is not able to hold the breath for a long time, a protocol with a wider collimation of 4 x 2.5 mm and a pitch of 6–7 is recommended. This will allow coverage of the central pulmonary vessels from the dome of the diaphragm to the top of the aortic arch within 6.4 and 4 seconds, respectively and will substantially reduce breathing artifacts.
For single-phase bolus injection, 150 mL of nonionic contrast material is injected at 4 mL (or more) per second. If this is immediately followed by injection of 40–60 mL of saline solution at the same injection rate, the bolus is flushed from the injection veins, resulting in a longer contrast plateau with fewer high-contrast artifacts. Semiautomatic bolus tracking with a region of interest in the right ventricle is generally used and is a very reliable technique in patients with accelerated pulmonary circulation.
Artifacts
Many factors can degrade the quality of pulmonary CT angiography, including inappropriate delivery of contrast material and artifacts related to pulsation, partial volume rendering, and breathing. Poor vascular enhancement resulting in nondiagnostic examinations may be due to low volumes of contrast material (<120 mL), low injection rates (<4 mL/sec), or incorrect bolus timing. Pulsation artifacts predominantly affect the lung parenchyma of the lingular segments of the left upper lobe, the middle lobe, and both lower lobes and are particularly severe in obliquely oriented vessels, which are also prone to partial volume artifacts. Pulsation artifacts can appear as intra- and paravascular streaks or vessel beading. Partial volume artifacts are increased by limited spatial resolution, resulting in stair-step and beading artifacts in oblique vessels on multiplanar reformatted or three-dimensional reformatted images (Fig 1). These artifacts are generally more severe in peripheral vessels. Breathing can periodically decrease vascular contrast material enhancement, and the resulting artifacts should not be mistaken for intraluminal filling defects (6–8). The overall accuracy of CT in the diagnosis of pulmonary vascular disorders increases with improved spatial resolution, administration of a contrast material bolus, and the use of cardiac gating.
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Figure 1a. Artifacts of small pulmonary vessels as seen on sliding thin-slab MIP images obtained from CT angiographic data. (a) Stair-step artifacts in oblique branches (arrowheads) due to insufficient spatial resolution. (b) Partial-volume and stair-step artifacts (arrowheads) give segments of vessels along the reconstruction plane a beaded appearance. (c) Pulsation of lung parenchyma around branches with partial volume rendering results in shifting of vessel segments with streaks (arrowheads) inside or next to the real vessel lumen. (Fig 1 reprinted, with permission, from reference 5.)
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Figure 1b. Artifacts of small pulmonary vessels as seen on sliding thin-slab MIP images obtained from CT angiographic data. (a) Stair-step artifacts in oblique branches (arrowheads) due to insufficient spatial resolution. (b) Partial-volume and stair-step artifacts (arrowheads) give segments of vessels along the reconstruction plane a beaded appearance. (c) Pulsation of lung parenchyma around branches with partial volume rendering results in shifting of vessel segments with streaks (arrowheads) inside or next to the real vessel lumen. (Fig 1 reprinted, with permission, from reference 5.)
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Figure 1c. Artifacts of small pulmonary vessels as seen on sliding thin-slab MIP images obtained from CT angiographic data. (a) Stair-step artifacts in oblique branches (arrowheads) due to insufficient spatial resolution. (b) Partial-volume and stair-step artifacts (arrowheads) give segments of vessels along the reconstruction plane a beaded appearance. (c) Pulsation of lung parenchyma around branches with partial volume rendering results in shifting of vessel segments with streaks (arrowheads) inside or next to the real vessel lumen. (Fig 1 reprinted, with permission, from reference 5.)
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CT Findings
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Classic Peripheral Pulmonary Embolism
Classic peripheral pulmonary embolism is encountered in 5%–30% of patients without evidence of central involvement (9–12). The appearances of small, peripheral endoluminal thromboemboli are similar to those seen in central pulmonary embolism (Fig 2a). However, smaller vessels are more prone to artifacts toward the periphery, and the presence of indirect signs of thromboembolism (asymmetric contrast enhancement in similar-sized branches with the same orientation, distal contrast enhancement recovery, normal enhancement in perpendicularly originating patent side branches) may aid in the diagnosis of peripheral emboli in otherwise equivocal cases (Fig 2b).
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Figure 2a. Peripheral pulmonary embolism. Sliding thin-slab MIP images were obtained from single-section CT angiographic data (section collimation, 1 mm; table feed, 3 mm; reconstruction increment, 0.5 mm). (a) Subsegmental (right anterior upper lobe subsegment) (double arrowheads) and subsubsegmental (left anterior upper lobe subsubsegment) (single arrowhead) embolism. Such findings can be emphasized with sliding thin-slab MIP performed parallel to vessel orientation if the vessel is occluded by embolic material. Identification of thrombotic material is more difficult in small peripheral "in-plane" vessels due to partial volume artifacts, stair-step artifacts, pulsation artifacts, and vessel beading. (b) In equivocal cases, subsegmental branches of similar size and orientation can help identify differences in contrast enhancement in vessels affected by emboli (arrowheads).
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Figure 2b. Peripheral pulmonary embolism. Sliding thin-slab MIP images were obtained from single-section CT angiographic data (section collimation, 1 mm; table feed, 3 mm; reconstruction increment, 0.5 mm). (a) Subsegmental (right anterior upper lobe subsegment) (double arrowheads) and subsubsegmental (left anterior upper lobe subsubsegment) (single arrowhead) embolism. Such findings can be emphasized with sliding thin-slab MIP performed parallel to vessel orientation if the vessel is occluded by embolic material. Identification of thrombotic material is more difficult in small peripheral "in-plane" vessels due to partial volume artifacts, stair-step artifacts, pulsation artifacts, and vessel beading. (b) In equivocal cases, subsegmental branches of similar size and orientation can help identify differences in contrast enhancement in vessels affected by emboli (arrowheads).
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Mosaic oligemia, a feature of chronic pulmonary embolism, is characterized by areas of reduced lung attenuation and reduced vessel diameter due to hypoperfusion and vasoconstriction. Noninvolved areas are hyperattenuating relative to pathologic hypoperfused areas and may be mistaken for areas of pathologic ground-glass attenuation. In mosaic oligemia, all lung areas change in attenuation equally with inspiration and expiration and do not demonstrate air trapping. Hence, without the need for additional proof of arterial thrombosis, a disparity in the size of segmental vessels in the presence of a mosaic pattern of variable lung attenuation without air trapping can help reliably distinguish chronic pulmonary embolism from other pulmonary abnormalities (Fig 3) (13).
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Figure 3a. Chronic pulmonary embolism. Axial single-section CT angiogram (section collimation, 1 mm; table feed, 3 mm; reconstruction increment, 0.5 mm) (a) and coronal reformatted image (b) demonstrate chronic pulmonary embolism with the classic mosaic perfusion pattern (ie, hypoperfusion of the affected lung segments and relative hyperperfusion of normal lung areas). Note that vessels in hypoattenuating lung areas are smaller in caliber than those in hyperattenuating areas.
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Figure 3b. Chronic pulmonary embolism. Axial single-section CT angiogram (section collimation, 1 mm; table feed, 3 mm; reconstruction increment, 0.5 mm) (a) and coronal reformatted image (b) demonstrate chronic pulmonary embolism with the classic mosaic perfusion pattern (ie, hypoperfusion of the affected lung segments and relative hyperperfusion of normal lung areas). Note that vessels in hypoattenuating lung areas are smaller in caliber than those in hyperattenuating areas.
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Pulmonary infarcts can complicate various peripheral pulmonary vascular disorders, including pulmonary embolism (Fig 4). CT findings are similar to findings at conventional radiography. Ground-glass attenuation can precede the typically segmental consolidation. Cavitation is observed frequently in septic infarcts, but it is rarely seen in bland infarcts.
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Figure 4a. Pulmonary embolism with infarcts. Coronal thin-slab MIP image obtained from single-section CT angiographic data (section collimation, 2 mm; table feed, 4 mm; reconstruction increment, 1 mm) (a) and corresponding axial image (soft-tissue windowing) (b) demonstrate infarction of the right posterior upper lobe segment. Pulmonary infarcts occur in pulmonary embolism if the bronchial artery collateral supply to the pulmonary parenchyma is insufficient. This is common in pulmonary infection or malignancy, which may induce bronchial artery thrombosis. Acute pulmonary infarction classically appears as wedge-shaped ground-glass attenuation with slightly increased volume initially (*), followed by consolidation and then volume loss and fibrosis or cavitation.
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Figure 4b. Pulmonary embolism with infarcts. Coronal thin-slab MIP image obtained from single-section CT angiographic data (section collimation, 2 mm; table feed, 4 mm; reconstruction increment, 1 mm) (a) and corresponding axial image (soft-tissue windowing) (b) demonstrate infarction of the right posterior upper lobe segment. Pulmonary infarcts occur in pulmonary embolism if the bronchial artery collateral supply to the pulmonary parenchyma is insufficient. This is common in pulmonary infection or malignancy, which may induce bronchial artery thrombosis. Acute pulmonary infarction classically appears as wedge-shaped ground-glass attenuation with slightly increased volume initially (*), followed by consolidation and then volume loss and fibrosis or cavitation.
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Pulmonary Arterial Hypertension
Regardless of the underlying pathologic changes, the basic radiologic pattern in chronic pulmonary arterial hypertension includes central pulmonary artery dilatation, tapering of peripheral pulmonary arteries, and right heart enlargement (Fig 5). The correlation between pulmonary artery dilatation and the degree of pulmonary hypertension at CT angiography is nonlinear. In adult patients, a distal main pulmonary artery (pulmonary artery trunk) diameter of at least 29 mm at its widest point has a positive predictive value of over 95%, and a distal main pulmonary artery width exceeding the diameter of the ascending aorta has a specificity of over 90% and a positive predictive value of over 95% (14,15). CT angiography and high-resolution CT play a central role in the diagnostic work-up of patients with pulmonary hypertension and are particularly important in identifying patients with chronic or recurrent pulmonary embolism and in preoperatively assessing patients as candidates for pulmonary thrombendatherectomy (16) or vascular interventional techniques such as stent placement or cutting balloon angioplasty. In addition, a variety of high-resolution CT and CT angiographic features can provide information about underlying disorders in patients with secondary pulmonary hypertension and facilitate differential diagnosis. The Table shows the CT morphologic criteria that aid in the diagnosis of primary pulmonary hypertension and the differential diagnosis of disorders underlying secondary pulmonary hypertension.
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Figure 5. Primary pulmonary hypertension in a 32-year-old woman with average systolic pulmonary arterial pressures of 140-150 mm Hg. CT scan shows enlargement of the central pulmonary arterial system with tapering to the periphery and corkscrew-shaped arteries. Peripheral plexiform arteriopathy (not shown) was also present. (Reprinted, with permission, from reference 5.)
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Sickle Cell Disease
Although sickle cell disease is not a primary embolic disorder, it is well recognized as a classic cause of recurrent pulmonary infarction. Irreversibly sickled cells increase in number with falling oxygen saturation (HbSS saturation of less than 85%), become more rigid, and aggregate in the peripheral arteriolar and capillary microcirculation. This initiates a vicious cycle of further sickling and occlusion, eventually resulting in tissue infarction. The lungs are among the four most frequently affected organs. Although in acute sickling crises there may be widespread pulmonary consolidation and infarcts, in our experience, the chronic pulmonary tissue damage results in multiple small peripheral infarctions and scars accompanied by more widespread signs of pulmonary fibrosis (Fig 6) (17). In the course of pulmonary thrombotic arteriopathy, patients with sickle cell disease can develop pulmonary arterial hypertension, probably with a poor prognosis (18).
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Figure 6a. Sickle cell disease in a 29-year-old woman. CT scans show multiple small peripheral pulmonary infarcts (arrowheads) following sickling crises. The scan in b also demonstrates widespread mild inter- and intralobular interstitial thickening associated with ground-glass attenuation, a finding that typically represents interstitial fibrosis.
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Figure 6b. Sickle cell disease in a 29-year-old woman. CT scans show multiple small peripheral pulmonary infarcts (arrowheads) following sickling crises. The scan in b also demonstrates widespread mild inter- and intralobular interstitial thickening associated with ground-glass attenuation, a finding that typically represents interstitial fibrosis.
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Embolism of Extravascular Origin
Septic Emboli.—
Sources of septic emboli include tricuspid valve endocarditis, septal defects, infected deep venous thrombosis, venous lines, and pacemaker wires. The diagnosis is classically made with blood culture, but CT abnormalities may be visible before blood cultures become positive and are therefore important for early diagnosis. Although none of the CT features is specific for septic emboli, they are often highly suggestive in the appropriate clinical setting (Fig 7) (19).
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Figure 7. Septic pulmonary embolism. CT scan shows mycotic pneumonia with infiltration or hemorrhage into the surrounding acini (halo sign) as well as solid and subsolid nodules (arrows). Additional CT findings that are suggestive of septic embolism include the feeding vessel sign, cavitating nodules, and small peripheral (cavitating) infarcts.
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Parasitic Emboli.—
Embolism of parasitic material per se is generally not associated with symptoms. The chest sequelae are related to the local pulmonary parasitic invasion or immune complex–mediated hypersensitivity. In addition, anaphylaxis to parasite components can occur with hydatid cyst rupture. Ascariasis and other nematode infections, schistosomiasis, and, rarely, hydatid disease (Echinococcus granulosus) (Fig 8) and amebiasis can embolize to the pulmonary circulation. Disseminated ascariasis can induce massive larval pulmonary embolism with superimposed pulmonary arterial thrombosis, resulting in sudden death (20). In chronic Schistosoma mansoni after development of portal hypertension with portosystemic shunting (most affected patients have normal liver function), pulmonary involvement by means of peripheral pulmonary arterial embolism occurs frequently. Pulmonary schistosomiasis originates from the arterioles and capillaries, causing fibrosis of the perivascular interstitium. The airways are rarely affected. The disease is characterized by diffuse zonal or geographic ground-glass attenuation, interlobular interstitial thickening, pulmonary fibrosis, nodules (sometimes calcifying), cavitation on rare occasions, pulmonary hypertension, and pulmonary arteriovenous communications resembling hepatopulmonary syndrome (21–25).
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Figure 8a. Parasitic pulmonary embolism. (a, b) CT scans demonstrate rupture of an Echinococcus cyst (E granulosus) (*) into the inferior vena cava ( in b). (c, d) CT scans show peripheral pulmonary embolism of scolices (c) with subpleural calcified daughter cysts (arrowheads in d). Massive central pulmonary arterial embolism can occur in hydatid disease or in ascariasis in association with acute pulmonary arterial thrombosis.
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Figure 8b. Parasitic pulmonary embolism. (a, b) CT scans demonstrate rupture of an Echinococcus cyst (E granulosus) (*) into the inferior vena cava ( in b). (c, d) CT scans show peripheral pulmonary embolism of scolices (c) with subpleural calcified daughter cysts (arrowheads in d). Massive central pulmonary arterial embolism can occur in hydatid disease or in ascariasis in association with acute pulmonary arterial thrombosis.
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Figure 8c. Parasitic pulmonary embolism. (a, b) CT scans demonstrate rupture of an Echinococcus cyst (E granulosus) (*) into the inferior vena cava ( in b). (c, d) CT scans show peripheral pulmonary embolism of scolices (c) with subpleural calcified daughter cysts (arrowheads in d). Massive central pulmonary arterial embolism can occur in hydatid disease or in ascariasis in association with acute pulmonary arterial thrombosis.
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Figure 8d. Parasitic pulmonary embolism. (a, b) CT scans demonstrate rupture of an Echinococcus cyst (E granulosus) (*) into the inferior vena cava ( in b). (c, d) CT scans show peripheral pulmonary embolism of scolices (c) with subpleural calcified daughter cysts (arrowheads in d). Massive central pulmonary arterial embolism can occur in hydatid disease or in ascariasis in association with acute pulmonary arterial thrombosis.
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Tumor Emboli.—
Pulmonary artery tumor emboli are encountered at autopsy in up to 30% of patients with underlying malignancies such as renal cell carcinoma; hepatocellular carcinoma; choriocarcinoma; carcinoma of the breast, stomach, or prostate gland; and malignant melanoma. Embolism occurs predominantly in small or medium-sized peripheral arteries, sometimes inducing pulmonary infarction. Tumor embolism to central vessels, like classic thromboembolism, is associated with a higher mortality rate. Although the presence of lymphangitic carcinomatosis is common, in some cases tumor embolism may be the only evidence of metastatic disease. CT angiography demonstrates dilated or beaded arteries with vascular occlusion (Fig 9) and, sometimes, evidence of pulmonary infarction (26,27).
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Figure 9a. Tumor embolism in a 43-year-old woman with breast cancer who presented with progressive dyspnea. (a) High-resolution CT scan demonstrates features of pulmonary lymphangitic carcinomatosis with irregular interlobular septal thickening in both upper lobes. (b) High-resolution CT scan shows extensive bilateral pulmonary artery tumor emboli, with nodular thickening of the pulmonary arteries along the bronchovascular bundles and terminal branching patterns peripherally. The bronchial walls are normal.
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Figure 9b. Tumor embolism in a 43-year-old woman with breast cancer who presented with progressive dyspnea. (a) High-resolution CT scan demonstrates features of pulmonary lymphangitic carcinomatosis with irregular interlobular septal thickening in both upper lobes. (b) High-resolution CT scan shows extensive bilateral pulmonary artery tumor emboli, with nodular thickening of the pulmonary arteries along the bronchovascular bundles and terminal branching patterns peripherally. The bronchial walls are normal.
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Foreign Material Embolism
Air can enter the pulmonary arterial system via the right heart as a complication of venous cannulation, surgery, delivery with placenta previa, and manual vaginal examination during late pregnancy and therapeutic air insufflation procedures. The fatal terminal vessel occlusion with fibrin plugs has been attributed to platelet damage by whipping. CT angiography is highly sensitive to the presence of small amounts of intravascular air in brachiocephalic veins, heart, or pulmonary arteries. This air can result from poor contrast material injection technique (26).
Talc, cellulose, and starch embolism can be seen in chronic drug abusers, who practice venous injection of drugs in tablet form that contain these materials as filler components, or with use of cotton as filter material. Embolization to pulmonary arterioles and capillaries causes obstruction and often thrombosis with transient pulmonary hypertension, acute pulmonary hypertension syndrome with sudden death, or chronic pulmonary hypertension (26,28,29).
Pulmonary mercury embolism can occur accidentally from venous sampling with mercury-sealed syringes or in patients who attempt suicide by venous injection. The diagnosis is generally made at conventional radiography and does not require CT (26,30–33).
Coils or other foreign bodies occasionally embolize to the pulmonary circulation as a result of attempted treatment of peripheral arteriovenous communications or systemic venous intervention. CT angiography is usually indicated to confirm the location of the coil in the chest and to exclude a pulmonary arteriovenous malformation (PAVM).
Pulmonary Arterial Thrombosis
Pulmonary arterial thrombosis without classic pulmonary embolism can occur as a complication of disorders such as pneumonia (especially tuberculosis), autoimmune-related or other thrombophilia (eg, systemic lupus erythematosus), and nephrotic syndrome). Bronchogenic carcinoma, primary pulmonary artery malignancy, pulmonary artery interruption, and massive parasitic embolism can also induce pulmonary arterial thrombosis. The prognosis of acute main pulmonary arterial thrombosis is poor, and sudden death is a well-documented complication (20). The CT angiographic appearance is identical to that of embolic occlusion that includes all peripheral arterial branches.
Pulmonary Vascular Tumor Invasion
Although tumor invasion of the central pulmonary artery can occasionally be seen in stage IV bronchogenic malignancy or metastatic disease (Fig 10), the preoperative identification of arterial wall infiltration presents a major diagnostic problem. CT angiography is often misleading in cases of extrinsic compression, and, conversely, does not display vascular involvement reliably except in advanced cases of intraluminal tumor growth. It remains unclear whether circumferential tumor encasement of the pulmonary artery is associated with a high rate of wall infiltration, as in the thoracic aorta. It is likely that endovascular or transesophageal ultrasound will be advantageous in this patient group (34). Peripheral pulmonary vascular tumor invasion can be demonstrated at high-resolution CT by the presence of perifocal pulmonary hemorrhage (Fig 10).
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Figure 10a. Pulmonary vascular tumor invasion. (a) CT angiogram obtained in a patient with bronchogenic carcinoma reveals advanced pulmonary artery tumor invasion (*). CT angiography is diagnostic in cases of intraluminal tumor. (b) CT scan obtained in a patient with neurofibromatosis I and metastatic schwannoma demonstrates perifocal ground-glass attenuation, a finding that reflects the presence of pulmonary hemorrhage. This CT feature is well recognized as a manifestation of peripheral invasion of pulmonary vessels in patients with high-grade malignancy.
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Figure 10b. Pulmonary vascular tumor invasion. (a) CT angiogram obtained in a patient with bronchogenic carcinoma reveals advanced pulmonary artery tumor invasion (*). CT angiography is diagnostic in cases of intraluminal tumor. (b) CT scan obtained in a patient with neurofibromatosis I and metastatic schwannoma demonstrates perifocal ground-glass attenuation, a finding that reflects the presence of pulmonary hemorrhage. This CT feature is well recognized as a manifestation of peripheral invasion of pulmonary vessels in patients with high-grade malignancy.
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Primary Malignancy of the Pulmonary Arteries
Leiomyosarcomas of the pulmonary arteries generally develop in the main or central pulmonary arteries, often in close relationship to the pulmonary valve. They can extend into the contralateral pulmonary artery or beyond the pulmonary valve into the right ventricle. In about 50% of cases, pulmonary artery leiomyosarcomas spread endoluminally to the periphery, obliterating the vessel. However, local pulmonary and bronchial invasion can occur, and the lung is frequently affected by metastasis. Secondary thromboembolic events are common and may be the only clinical evidence of tumor at presentation, with clinical features similar to those of recurrent classic pulmonary embolism. The age distribution of pulmonary artery leiomyosarcomas peaks after 30 years. In our experience, all four patients displayed a centrifugal growth pattern with evidence of arterial dilatation secondary to the intravascular tumor mass, distal thrombosis or thromboembolism, and, in one patient, pulmonary metastasis (Figs 11, 12). In all cases, there was sufficient proximal tumor with contrast enhancement to allow differentiation from classic pulmonary embolism. Differentiation of metastatic tumor emboli from an unknown primary tumor may be difficult; however, dilatation of peripheral vessels as seen in tumor embolism is not a common feature of leiomyosarcoma of the pulmonary artery (26, 27).
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Figure 11a. Leiomyosarcoma of the pulmonary artery in a patient with pulmonary metastatic disease. Single-section CT angiograms (section collimation, 3 mm; table feed, 5 mm; reconstruction increment, 2 mm) obtained 5 months after attempted pulmonary endatherectomy for suspected recurrent pulmonary embolism show recurrent bilateral pulmonary artery tumors. Tuberous segmental pulmonary artery expansion by the tumor nodules (*) is also noted. Enhancement is present in the right lower lobe artery nodule (arrowheads in a).
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Figure 11b. Leiomyosarcoma of the pulmonary artery in a patient with pulmonary metastatic disease. Single-section CT angiograms (section collimation, 3 mm; table feed, 5 mm; reconstruction increment, 2 mm) obtained 5 months after attempted pulmonary endatherectomy for suspected recurrent pulmonary embolism show recurrent bilateral pulmonary artery tumors. Tuberous segmental pulmonary artery expansion by the tumor nodules (*) is also noted. Enhancement is present in the right lower lobe artery nodule (arrowheads in a).
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Figure 12a. Leiomyosarcoma of the pulmonary artery. (a) Multisection CT angiogram (section collimation, 4 x 1 mm; table feed, 6 mm; reconstruction increment, 0.7 mm) shows a right main pulmonary artery tumor (*) with unenhanced apposition thrombus (arrowheads) across the main pulmonary artery bifurcation. The tumor appears as an expansile enhancing clot with protrusion into the main pulmonary artery bifurcation. (b) Coronal thick-slab MIP image demonstrates lack of contrast enhancement in the right peripheral pulmonary vessels, probably due to thrombosis of the right peripheral branches. (Fig 12 reprinted, with permission, from reference 5.)
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Figure 12b. Leiomyosarcoma of the pulmonary artery. (a) Multisection CT angiogram (section collimation, 4 x 1 mm; table feed, 6 mm; reconstruction increment, 0.7 mm) shows a right main pulmonary artery tumor (*) with unenhanced apposition thrombus (arrowheads) across the main pulmonary artery bifurcation. The tumor appears as an expansile enhancing clot with protrusion into the main pulmonary artery bifurcation. (b) Coronal thick-slab MIP image demonstrates lack of contrast enhancement in the right peripheral pulmonary vessels, probably due to thrombosis of the right peripheral branches. (Fig 12 reprinted, with permission, from reference 5.)
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Pulmonary Neoplasms of Vascular Tissue
Kaposi sarcoma is a polyclonal neoplasm that derives from primitive vasoformative mesenchyme or endothelial or pericytic cells of small vessels. Pulmonary involvement is frequent in the disseminated form of the disease and occurs in up to 50% of acquired immunodeficiency syndrome (AIDS) patients with Kaposi sarcoma (19). At clinical examination, symptoms are relatively minor compared to the extent of tumoral involvement, although fatal pulmonary hemorrhage in advanced stages has been reported. Either bronchoscopic evidence of intraluminal Kaposi sarcoma or transbronchial or more invasive biopsy is required for the diagnosis. Conventional radiography can be as helpful as high-resolution CT, displaying a typical flamelike pattern of a persistent perihilar mass or ill-defined pulmonary nodules. Lymphadenopathy, pneumonic infiltrates, and pleural effusion are frequently present (35–38). The characteristic high-resolution CT appearance is frequently masked by superimposed pneumonia due to endoluminal spread of infection (in most cases, Pneumocystis carinii pneumonia) and to endobronchial tumor growth and postobstructive pneumonia. High-resolution CT demonstrates irregular, ill-defined peribronchovascular nodules, often larger than 1 cm (39) with surrounding ground-glass attenuation, with air bronchograms especially in larger peripheral or coalescent perihilar masses. Smooth or nodular peribronchovascular interstitial thickening and interlobular septal thickening are frequently present (Fig 13). The high-resolution CT findings in AIDS patients have a diagnostic accuracy greater than 90% (40).
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Figure 13. Pulmonary Kaposi sarcoma in a patient with AIDS. Bronchoalveolar lavage was negative for P carinii pneumonia. High-resolution CT scan demonstrates interstitial thickening in a perihilar and peribronchovascular distribution and coalescent masslike alveolar attenuation, findings that raised suspicion for Kaposi sarcoma. As in this case, the presence of superimposed infection can obscure radiologic findings, and often the characteristic flamelike appearance of nodular areas or perihilar attenuation is not present. The diagnosis of Kaposi sarcoma was confirmed at postmortem examination. (Reprinted, with permission, from reference 5.)
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Other neoplasms of primary vascular origin include hemangiopericytoma, angiosarcoma, proliferating (systemic, malignant) angioendothelio-matosis, and epithelioid hemangioendothelioma. These neoplasms are exceedingly rare, and the data in the literature are scarce. Radiologic features at presentation range from a more or less peripheral solitary mass to multiple masses or a very large pulmonary mass that can be well or poorly defined at conventional radiography and CT (hemangiopericytoma, angiosarcoma, epithelioid hemangioendothelioma). Proliferating angioendotheliomatosis can resemble interstitial pneumonia at conventional radiography. Occurrence of all four neoplasms in childhood or adolescence has been reported. The diagnosis is generally made at histologic analysis, but the CT morphologic features (eg, tumor calcification or perifocal pulmonary hemorrhage in epithelioid hemangioendothelioma) or the clinical manifestation (eg, pulmonary hypertension in proliferating angioendotheliomatosis) can give important clues and aid in the differential diagnosis (26,41–51).
Pulmonary Arteriovenous Shunting
PAVMs are, in the majority of cases, associated with Rendu-Weber-Osler disease. Many PAVMs are discovered incidentally in adulthood, with patients often being asymptomatic due to accommodation to the chronic pulmonary hypoxemia. CT angiography performed in conjunction with conventional angiography has an important role in screening for PAVMs, with a sensitivity greater than 95% (52). CT angiography facilitates planning of transarterial embolization by providing three-dimensional images of complex malformations (Fig 14). These 3D images are especially helpful in malformations with more than one feeding vessel. A diameter of 3 mm or more for the feeding PAVM vessels is considered an indication for embolization (53). Untreated or occult PAVMs can increase in size over time, with increasing shunt volumes inducing hypoxemia, together with an increased risk of stroke and PAVM rupture (Fig 15).
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Figure 14. Multiple peripheral PAVMs in a patient with Rendu-Weber-Osler disease. Coronal volume-rendered image (posterior view) obtained from multisection CT angiographic data (section collimation, 4 x 1 mm; table feed, 6 mm; reconstruction increment, 0.7 mm) clearly depicts serpiginous peripheral pulmonary vessels (arrowheads), the supplying and draining branches and the vascular segments of arteriovenous communication. Two PAVMs have been treated with coil embolization (arrows). (Reprinted, with permission, from reference 5.)
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Figure 15. PAVM rupture in a 63-year-old man who presented with acute hemothorax. The patient had no previous history of or clinical suspicion for arteriovenous malformation. CT scan demonstrates a ruptured large PAVM (*), a finding that was confirmed at lobectomy.
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Diffuse pulmonary arteriovenous shunting can occur in pregnancy, Rendu-Weber-Osler disease, complex cardiac malformations, proximal pulmonary artery interruption, polysplenia syndrome, liver disease, and chronic schistosomiasis (54–63). Patients present with severe hypoxemia and commonly have a history of systemic embolism with neurologic complications. Although coil embolization can successfully reduce hypoxemia in some cases, flow redistribution surgery may be more appropriate for preventing neurologic complications (54). Spontaneous regression after pregnancy has been reported (60). In macroscopic diffuse shunting, CT angiography displays conglomerate areas of small, weblike dilated arteries (Fig 16). Digital subtraction angiography is required to assess morphologic features and flow characteristics prior to coil embolization of larger communications. Diffuse telangiectatic microshunting may be evident only from the histologic findings. As an alternative to pulmonary angiography, contrast material–enhanced echocardiography or microsphere nuclear imaging can be used to assess right-to-left shunting, which can provide information about shunt volume during rest and exercise.
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Figure 16a. Diffuse pulmonary arteriovenous shunting in a 28-year-old pregnant woman. Axial (a) and sagittal (b) sliding thin-slab MIP images obtained from ultra-low-dose multisection CT data (effective dose <0.5 mSv) show dilatation of pulmonary arteries and veins in the right lower lobe (*) with a reticular vascular pattern in the lung periphery (arrowheads). (Fig 16 reprinted, with permission, from reference 5.)
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Figure 16b. Diffuse pulmonary arteriovenous shunting in a 28-year-old pregnant woman. Axial (a) and sagittal (b) sliding thin-slab MIP images obtained from ultra-low-dose multisection CT data (effective dose <0.5 mSv) show dilatation of pulmonary arteries and veins in the right lower lobe (*) with a reticular vascular pattern in the lung periphery (arrowheads). (Fig 16 reprinted, with permission, from reference 5.)
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Hepatopulmonary syndrome is characterized by pulmonary hypoxemia in the presence of advanced liver disease and is caused by (generally subpleural) arteriovenous microshunts that resemble spider angiomas. Patients present with gradual onset of hypoxemia and with dyspnea that is commonly more severe in the upright position. CT angiography can demonstrate the presence of centrilobular vessel–associated micronodules connected by arcade-like dilated subpleural vascular branches, predominantly within the lower lobes (Fig 17) (64,65).
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Figure 17. Hepatopulmonary syndrome in a patient with advanced liver cirrhosis and clinical evidence of right-to-left shunting. Sliding thin-slab MIP image obtained from single-section CT angiographic data (section collimation, 1 mm; table feed, 3 mm; reconstruction increment, 0.5 mm) demonstrates centrilobular vessel-associated micronodules connected by multiple arcade-like dilated subpleural vessels in the lower lobe (arrowheads).
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Pulmonary Vasculitis
Takayasu arteritis type IV (66) and giant cell arteritis are vasculitic syndromes affecting the central pulmonary arterial system (large elastic and medium-sized muscular branches). They are characterized by wall thickening and stenotic changes, which can cause peripheral perfusion asymmetry (Fig 18) and arterial thrombosis or thromboembolism with distal pulmonary infarction.
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Figure 18a. Takayasu arteritis. (a) Axial sliding thin-slab MIP image obtained prior to steroid therapy shows central pulmonary arterial wall thickening (arrowheads) and tapering of the lumen at the pulmonary artery bifurcation and left and right main arteries. (b) Axial sliding thin-slab MIP image obtained after corticosteroid and immunosuppressive therapy and right pulmonary artery stent placement (*) shows improvement in the caliber of the central and peripheral pulmonary arteries of the right lung (arrows). (Fig 18 reprinted, with permission, from reference 5.)
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Figure 18b. Takayasu arteritis. (a) Axial sliding thin-slab MIP image obtained prior to steroid therapy shows central pulmonary arterial wall thickening (arrowheads) and tapering of the lumen at the pulmonary artery bifurcation and left and right main arteries. (b) Axial sliding thin-slab MIP image obtained after corticosteroid and immunosuppressive therapy and right pulmonary artery stent placement (*) shows improvement in the caliber of the central and peripheral pulmonary arteries of the right lung (arrows). (Fig 18 reprinted, with permission, from reference 5.)
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Systemic vascular involvement in polyarteritis nodosa (PAN) is characterized by vasculitis of small to medium-sized vessels with sparing of arterioles and capillaries. Involvement of the pulmonary arteries is rare. Bronchial arteries are more frequently involved. The mixed interstitial-alveolar infiltrates seen on rare occasions resemble areas of pneumonitis with diffuse alveolar damage or fibrosis (Fig 19) (67,68).
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Figure 19a. PAN in a 15-year-old boy. Selective pulmonary arteriography was normal. (a) Axial sliding thin-slab MIP image obtained from single-section spiral CT data (section collimation, 2 mm; table feed, 4 mm; reconstruction increment, 1 mm) prior to therapy shows lobular and small geographic areas of ground-glass attenuation at pulmonary vascular bifurcations, findings that represent focal pneumonitis (confirmed at open lung biopsy). (b) Axial sliding thin-slab MIP image obtained 3 weeks after corticosteroid and immunosuppressive therapy demonstrates marked improvement. (c) Corresponding renal digital subtraction angiogram demonstrates multiple microaneurysms with a pearllike configuration.
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Figure 19b. PAN in a 15-year-old boy. Selective pulmonary arteriography was normal. (a) Axial sliding thin-slab MIP image obtained from single-section spiral CT data (section collimation, 2 mm; table feed, 4 mm; reconstruction increment, 1 mm) prior to therapy shows lobular and small geographic areas of ground-glass attenuation at pulmonary vascular bifurcations, findings that represent focal pneumonitis (confirmed at open lung biopsy). (b) Axial sliding thin-slab MIP image obtained 3 weeks after corticosteroid and immunosuppressive therapy demonstrates marked improvement. (c) Corresponding renal digital subtraction angiogram demonstrates multiple microaneurysms with a pearllike configuration.
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Figure 19c. PAN in a 15-year-old boy. Selective pulmonary arteriography was normal. (a) Axial sliding thin-slab MIP image obtained from single-section spiral CT data (section collimation, 2 mm; table feed, 4 mm; reconstruction increment, 1 mm) prior to therapy shows lobular and small geographic areas of ground-glass attenuation at pulmonary vascular bifurcations, findings that represent focal pneumonitis (confirmed at open lung biopsy). (b) Axial sliding thin-slab MIP image obtained 3 weeks after corticosteroid and immunosuppressive therapy demonstrates marked improvement. (c) Corresponding renal digital subtraction angiogram demonstrates multiple microaneurysms with a pearllike configuration.
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Microscopic polyangiitis, a nongranulomatous antineutrophil cytoplasmic antibody (ANCA)–associated systemic vasculitis, is characterized clinically by the presence of renal disease, pulmonary hemorrhage, and, frequently, peripheral neuropathy, gastrointestinal disorders, and disorders of the ear, nose, and throat. In many cases, recurrent lung hemorrhage (Fig 20) progresses to pulmonary fibrosis by the same mechanism as described for idiopathic pulmonary hemosiderosis (69). In the intermediate phase, high-resolution CT scans can be normal or display centrilobular ground-glass attenuation representing the inflammatory infiltrate or diffuse interstitial fibrosis.
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Figure 20a. Active ANCA-positive microscopic polyangiitis in a 57-year-old man with hemoptysis. CT scans display focal perivascular areas of ground-glass attenuation in a peripheral (a) and perihilar (b) distribution (arrows), findings that are consistent with pulmonary hemorrhage.
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Figure 20b. Active ANCA-positive microscopic polyangiitis in a 57-year-old man with hemoptysis. CT scans display focal perivascular areas of ground-glass attenuation in a peripheral (a) and perihilar (b) distribution (arrows), findings that are consistent with pulmonary hemorrhage.
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Wegener disease is a mixed vasculitic and granulomatous disorder. In the acute stage, it can appear as lobular pulmonary hemorrhage (Fig 21). (Because of space limitations, we can present features of only the most vasculitic end of the spectrum of pulmonary manifestations in Wegener disease.) In addition to its diagnostic value, high-resolution CT may play a future role in long-term surveillance of patients with Wegener disease (70,71).
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Figure 21a. Wegener vasculitis. (a) CT scan shows focal pulmonary hemorrhage with lobular ground-glass attenuation (arrowheads). A perivascular distribution, which is a feature of PAN, is not obvious in Wegener disease. (b) CT scan obtained in a different patient demonstrates subacute-chronic pulmonary hemorrhage with widespread consolidation and interstitial areas of increased attenuation that include the interlobular septa.
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Figure 21b. Wegener vasculitis. (a) CT scan shows focal pulmonary hemorrhage with lobular ground-glass attenuation (arrowheads). A perivascular distribution, which is a feature of PAN, is not obvious in Wegener disease. (b) CT scan obtained in a different patient demonstrates subacute-chronic pulmonary hemorrhage with widespread consolidation and interstitial areas of increased attenuation that include the interlobular septa.
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Churg-Strauss syndrome is characterized by a systemic necrotizing vasculitis of small arteries and veins in patients with asthma and blood eosinophilia. Asthma is normally the first clinical manifestation, but the interval to vasculitis can span several decades. A forme fruste has been described without asthma. Lesions in the lungs resemble eosinophilic pneumonia and can typically change in distribution in a matter of weeks. An overlap with Loeffler syndrome is well recognized. The diagnosis is made on the basis of clinical and radiologic findings and results of open lung biopsy. Findings at high-resolution CT include multifocal fluctuant consolidation (59% of cases) (Fig 22), pleural effusion (12%), centrilobular micronodules (12%), and interlobular septal thickening (6%). Cavitation occurs infrequently in the course of the disease (71,72).
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Abstract
LEARNING OBJECTIVES FOR TEST...
