The Core Curriculum: Cardiopulmonary Imaging, 1st Edition (2004)

Chapter 21. Pulmonary Vascular Disease

Pulmonary vascular disease is often overlooked as an etiology for chest pain and dyspnea. Conditions may be life threatening, in the case of acute pulmonary embolism (PE), or may be the cause of chronic symptoms, in the case of pulmonary hypertension and chronic PE. In this chapter we discuss acute and chronic PE, pulmonary arterial hypertension (PAH), and briefly touch on the congenital and acquired abnormalities of the pulmonary arteries, including pulmonary arteriovenous malformations (AVMs), tumor embolism, and stenosis, aneurysms, and tumors of the pulmonary arteries.

Pulmonary Thromboembolic Disease

PE is the third most common acute cardiovascular disease after ischemic heart disease and stroke, and is an important cause of patient morbidity and mortality. The incidence of PE is 600,000 annually in the U.S., and the mortality of untreated PE approximately 30% (1). Hence, it is prudent to diagnose PE accurately and quickly, and to initiate treatment in a timely fashion. Accurate diagnosis is imperative, not only to decrease the morbidity and mortality after treatment, but to avoid the risks of hemorrhage associated with anticoagulation seen in up to 7% of patients, especially in the case of a false-positive test result for PE.

The diagnosis of acute PE continues to pose a challenge to clinicians and radiologists. Ancillary tests include the electrocardiogram, which may demonstrate a right heart strain pattern, and the blood test D-dimer, which when negative is useful to exclude venous thrombosis. However, the D-dimer test is nonspecific and may also be abnormal with myocardial infarction, pneumonia, heart failure, cancer, and recent surgery (2,3).

Venous thrombi form most commonly in veins of the lower extremities and pelvis and then dislodge, propagating cranially into the pulmonary arterial tree. Radiologic evaluation of the patient may include evaluation of the thorax with chest radiography, ventilation-perfusion (V/Q) scans, computed tomography (CT), and magnetic resonance imaging (MRI) and evaluation of the lower extremity veins with CT venography, MR venography, or ultrasound.

Radiology plays a major role in the diagnosis of PE, and the ubiquitous chest radiograph is the first investigation of choice. V/Q scintigraphy has played a major role in the diagnosis of PE. Though angiography is the standard of reference, it is infrequently used (4,5). The advent of newer helical scanners, electron beam scanners, and particularly multidetector helical scanners has significantly changed the way PE is diagnosed. Multidetector CT is now routinely used in the diagnosis of PE. Magnetic resonance angiography may also be used in the diagnosis of PE and is particularly useful in cases where there is a history of allergy to iodinated contrast media. Transthoracic and transesophageal echocardiography are useful in the diagnosis of large central PE in patients with acute right heart strain and right heart failure. Transesophageal echocardiography can be performed at the bedside and is particularly helpful in medically unstable patients.

Ultrasound venography is now used as the primary modality for the diagnosis of deep vein thrombosis (DVT) of the lower extremities and has virtually replaced the more invasive direct catheter venography. Magnetic resonance venography is useful, particularly in patients where ultrasound is difficult due to body habitus. Similarly, indirect CT venography is used for evaluating DVT in combination with a CT pulmonary angiogram (CTPA), giving CT the advantage of imaging both the thrombus burden in the extremities and pelvis and the pulmonary arterial tree in a single comprehensive examination. The goal in evaluating suspected venous thromboembolic disease is to have a cost-effective noninvasive test with high sensitivity and specificity.

Etiology and Pathophysiology

PE and DVT are a spectrum of the same disease process, best described as venous thromboembolic disease. PE is a consequence of thrombus, most commonly formed in the deep veins of the pelvis and lower extremities. Thrombus can also originate in the veins of the head, neck, upper extremities, inferior vena cava, right atrium, and right ventricle. Risk factors for DVT are listed in Table 21.1.

In most fatal PE, at autopsy the thrombus is localized proximal to the knee (6). After dislodgement, the venous thrombus propagates through the right heart and into the pulmonary arterial circulation, usually lodging in the main, lobar, or segmental pulmonary arteries, and as a shower of emboli into the subsegmental and smaller pulmonary arteries. In some cases, this leads to acute right ventricular failure. Fatal PE results as a consequence of central occlusive thrombus in patients with normal cardiopulmonary reserve but may also occur with smaller occlusive thrombi in patients with underlying cardiopulmonary compromise. In the uncommon event of a patent foramen ovale, atrial septal defect, or ventricular septal defect, paradoxical emboli may be seen resulting in stroke and mesenteric and renal ischemia.

Pulmonary emboli are more often multiple than solitary and occur more often in the right lung than the left lung. They are most frequently found in the lower lobes, probably due to the greater pulmonary blood flow to the lower lobes. Pulmonary hemorrhage, infarction, or atelectasis may occur as a consequence of PE. Acute PE is treated with either anticoagulation or, if contraindicated, with an inferior vena cava filter. Treatment with anticoagulants prevents more clot forming while the body dissolves the clot. If this fails, intravenous thrombolysis with recombinant tissue plasminogen activator may be given over a period of 8 to 12 hours and occasionally up to 24 hours in hemodynamically stable patients. In hemodynamically unstable patients, intraarterial thrombolysis as a part of thrombectomy may be performed, with the thrombolytic agent directly injected into the thrombus. Surgical embolectomy may be required in large occlusive PE and carries a high mortality. If thrombolysis fails to resolve the emboli, chronic thromboembolic pulmonary hypertension (CTEPH) may ensue.

Pulmonary emboli are usually multiple and located in areas of greatest pulmonary blood flow.

Table 21.1: Risk Factors for Pulmonary Thromboembolic Disease

Venous stasis
   Immobilization
   Surgery
   Long airplane flights
Malignancy
Indwelling catheters
Abnormality of the wall of the veins (such as thrombophlebitis)
Hypercoagulable states
   Pregnancy
   Oral contraceptive pills
   Antithrombin C
   Protein C and S deficiency

Clinical Presentation

The clinical manifestations of PE are nonspecific and include dyspnea, chest pain that is often pleuritic in nature, hemoptysis, cough, syncope, or even death. Tachypnea, tachycardia, atrial fibrillation, hypotension, fever, and a pleural friction rub may be noted on physical examination (7). Because of the nonspecific nature of the signs and symptoms, the diagnosis is often overlooked or confused with other diagnoses. Arterial oxygen saturation is often low, especially in cases of significant PE. The electrocardiogram may demonstrate tachycardia, atrial fibrillation, or a right heart strain pattern with S1Q3T3 pattern or a new right bundle branch block; more commonly the electrocardiogram is normal.

Radiology in the Diagnosis of Acute Pulmonary Embolism

Chest Radiograph

Although the chest radiograph is usually the first imaging examination performed in patients with suspected PE, it may be completely normal even in the presence of near fatal PE. When abnormal, the findings are usually nonspecific. Chest radiographic findings are uncommon due to the dual blood supply from bronchial arteries. The main use of a chest radiograph is to exclude other disease processes that mimic the clinical signs and symptoms of PE, such as pneumonia, pneumothorax, rib fractures, aortic dissection, pleural effusions, pericardial effusion, tumor, and hiatal hernia (8). The radiograph is used in conjunction with the V/Q scan in the evaluation of PE, because it is used in the interpretation scheme for V/Q scans (9).

Chest radiographs in patients with suspected PE are most useful to exclude other disease processes that may be causing symptoms, such as pneumonia or edema.

No chest radiograph, normal or abnormal, can be used to exclude PE.

The chest radiograph findings are given in Table 21.2. Historical findings of PE on chest radiography are rarely encountered (Table 21.2), such as the Westermark sign, which is pulmonary oligemia distal to an obstructing embolus (Fig. 21.1), and the Fleischner sign, which is a large central pulmonary artery due to central thrombus with abrupt tapering, also known as the knuckle sign. These signs are mainly seen when there is PE without infarction. The Hampton hump, a wedge-shaped pleural based opacity with the apex pointing toward the hilum and the base abutting the pleura, particularly along the diaphragmatic pleura, is highly suggestive of pulmonary infarction. Pulmonary infarcts maintain their shape as they resolve, which may take several months. Occasionally, an infarct is mistaken for a solitary pulmonary nodule. Although most infarcts resolve completely, many leave an area of linear scar and occasionally a small nodule.

Westermark sign, Fleischner sign, and Hampton hump are classic but very uncommon radiographic findings of PE.

Table 21.2: Chest Radiograph Findings of Acute Pulmonary Embolism

Specific Findings

Nonspecific Findings

Westermark sign

Atelectasis

Fleischner sign

Elevated hemidiaphragm

Hampton hump

Pleural effusion(s)
Dilated central pulmonary arteries

Figure 21.1 Westermark sign. Chest radiograph demonstrates pulmonary oligemia in the right mid-lung, secondary to central right pulmonary embolus.

The nonspecific radiograph findings in PE with infarction include an elevated hemidiaphragm, pleural effusion, and atelectasis. Pleural effusions are quite common and are often small and unilateral. These often occur early and are frequently hemorrhagic. Occasionally, they can be large or bilateral. Effusions may be an isolated finding in up to one-third of patients with PE and are seen in approximately two-thirds of patients when accompanied by pulmonary hemorrhage or infarction.

Most chest radiographs in pulmonary embolism are nonspecific.

In the original Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study, the sensitivity and specificity of the V/Q lung scan was determined using pulmonary angiogram as the gold standard in the evaluation of suspected acute PE (10). The study concluded that clinical assessment combined with the V/Q scan established or excluded the diagnosis of acute PE in only a small number of patients. A normal chest radiograph was uncommon, found in 12% of patients. Radiographic signs poorly correlate with the diagnosis of PE and did not help to confirm or exclude the diagnosis of PE.

Radionuclide Imaging

The principle underlying V/Q scintigraphy in the diagnosis of PE is the detection of decreased or absent perfusion, with corresponding normal ventilation. Perfusion scintigraphy is performed by intravenous injection of technetium-99m–labeled albumin macroaggregates ranging from 10 to 100 μm in size. These microparticles lodge in the precapillary arterioles of the pulmonary vascular bed. Eight static views are obtained (anterior, posterior, both laterals, and both anterior and posterior obliques). Ventilation scintigraphy is most often obtained after inhalation of radiolabeled gas such as xenon-133 or aerosols such as technetium-99m diethylenetriaminepentaacetic acid or technetium-99m pyrophosphate. Again, eight images are obtained as above, preferably in the upright position and especially with xenon. A normal V/Q scan is illustrated in Fig. 21.2.

Although the diagnosis of PE is based on a mismatched perfusion defect (i.e., perfusion defect in an area that is normally ventilated), the test is not specific for the diagnosis of PE. Most V/Q scan interpretations require interpretation in conjunction with a current chest radiograph. The current criteria used in the diagnosis of PE are the revised PIOPED criteria (11,12) (Table 21.3). Using these criteria, a V/Q scan is labeled as normal, very low probability, low probability, intermediate/indeterminate probability (Fig. 21.3), and high probability (Fig. 21.4) for the diagnosis of PE. Although a normal V/Q scan virtually excludes a PE and a high probability scan confirms a PE, in the PIOPED study only 14% of patients had a normal V/Q scan and 13% of patients had a high probability V/Q scan. The other 73% of patients had an indeterminate V/Q scan, a nonconclusive result requiring further evaluation with other studies, such as pulmonary angiography.

V/Q scans for PE are most specific when perfusion defects occur in areas of normal ventilation.

 

Pulmonary Angiography

Pulmonary angiography is considered the reference test for the diagnosis of PE, against which all other tests are compared. Pulmonary angiography is recommended when there is an indeterminate V/Q scan, a discordance between the V/Q result (low probability, very low probability), and a high clinical suspicion for PE, indeterminate CTPA, or in cases of acute massive PE. It is particularly useful when catheter-guided thrombolysis or catheter-guided thrombectomy with direct injection of thrombolytic agent into the thrombus is to be performed. An invasive test, it requires a venous puncture usually at the groin and placement of a catheter through the right atrium and right ventricle into the main pulmonary artery, followed by selective placement in the right and left pulmonary arteries. Passage through the heart may induce an arrhythmia, including right bundle branch block. Therefore, patients with left bundle branch block should have a pacemaker in during the procedure. Contrast media is then injected and images obtained in the anteroposterior and oblique projections of each lung. It is a relatively safe invasive test, with a low mortality rate of 0.5% and morbidity rate of 3% to 5%, but is an extremely underused modality, used in only 12% to 14% of patients with nondiagnostic V/Q scans (4,13,14,15). Pulmonary angiography allows direct visualization of the clot burden. The angiographic signs of PE are a filling defect within an opacified pulmonary artery (Fig. 21.5) or occlusion of a pulmonary arterial branch (16,17). Absent or reduced opacification of small arterial branches is sometimes seen, corresponding to a perfusion defect on perfusion scintigraphy. A good quality negative pulmonary angiogram virtually excludes PE. However, angiography has its limitations. It is an invasive test that is underused and not available at all centers.

Figure 21.2 Normal ventilation-perfusion scan. A. Ventilation scan, with uniform uptake of technetium-99m diethylenetriaminepentaacetic acid. B. Perfusion scan, with uniform uptake of Tc microaggregates of albumin. (Courtesy of Dr. C. Bui, Ann Arbor, MI.)

Table 21.3: Revised PIOPED Ventilation Perfusion Interpretation Categories and Criteria

High probability

≥2 large (>75% of a segment) segmental equivalent perfusion defects substantially larger than corresponding ventilation or radiographic abnormalities or without any ventilation or radiograph abnormalities.

Intermediate/indeterminate probability

0.5 to 1.5 mismatched segmental equivalent perfusion defects. This may be 1 large plus 1 moderate mismatched perfusion defects, or 1 to 3 moderate.
Solitary moderate or large segmental size triple match in lower lobe.
Multiple opacities with associated perfusion defects.

Low probability

A single large or moderate size matched segmental defect.
>3 small segmental perfusion defects (< 25% of a segment) with a normal chest radiograph.
Moderate sized pleural effusion with no other perfusion defect in either lung.

Very low probability

Nonsegmental lesion, linear atelectasis, costophrenic angle effusion with no other perfusion defect in either lung.
> 2 VQ matched defects with normal chest x-ray.
1–3 small segmental perfusion defects.
Solitary triple matched defect in the mid or upper lung zone.

Normal

No perfusion defects present.

VQ, ventilation perfusion.
From Gottschalk A, Stein PD, Henry JW, et al. Matched ventilation, perfusion and chest radiographic abnormalities in acute pulmonary embolism. J Nuclear Med 1996;37:1636–1638Stein PD, Relyea B, Gottschalk A. Evaluation of individual criteria for low probability interpretation of ventilation-perfusion lung scans. J Nuclear Med 1996;37:577–581; and Gottschalk A, Sostman HD, Coleman RE, et al. Ventilation-perfusion scintigraphy in the PIOPED study. Part II. Evaluation of the scintigraphic criteria and interpretations. J Nuclear Med 1993;34:1119–1126, with permission.

Pulmonary angiography is the reference test (gold standard) for the diagnosis of PE.

Pulmonary angiography is underused in the diagnosis of PE.

 

Computed Tomography

PE has incidentally been encountered on thoracic CT examinations as early as 1978. With the advent of new, faster, helical CT scanners, the ability of CT to detect PE as a primary test has received a great deal of interest (18,19). Techniques and scanners have evolved over the last decade; since the introduction of four-row multidetector and greater detector CT scanners, CT has taken on a more dominant role in the evaluation of suspected PE, right down to the subsegmental level (20). CTPA has been almost as reliable as pulmonary angiography in the detection of PE up to the segmental level; with multidetector CT, this reliability may also extend to the subsegmental level (21). Up to one-third of cases at the subsegmental level are misdiagnosed, even at pulmonary angiography (10). With thinner collimation, subsegmental emboli can be seen in 61% to 70% of cases (19,22). There is ongoing debate about the clinical significance of isolated subsegmental PE and whether these should be treated. Treatment may especially benefit patients with cardiopulmonary compromise; in patients with normal cardiopulmonary physiology there is more debate.

Figure 21.3 Intermediate probability ventilation-perfusion scan. (A) Ventilation and (B) perfusion scans demonstrate multiple small mismatched defects (arrows). (Courtesy of Dr. C. Bui, Ann Arbor, MI.)

Figure 21.4 High probability ventilation-perfusion scan. A. Normal ventilation scan with uniform uptake of technetium-99m diethylenetriaminepentaacetic acid. B. Perfusion scan demonstrating multiple defects (arrows) that are mismatched, compatible with acute pulmonary embolism. (Courtesy of Dr. C. Bui, Ann Arbor, MI.)

Figure 21.5 Acute pulmonary embolism on pulmonary angiogram. A. Right and (B) left pulmonary artery selective injections demonstrating multiple filling defects (arrows) and vessel cutoff sign (arrowheads). (Courtesy of Dr. K. Cho, Ann Arbor, MI.)

Helical Computed Tomography Pulmonary Angiogram

Iodinated contrast, 120 to 150 mL, is usually injected via the antecubital vein, at 4 to 5 mL/s. The timing of intravenous contrast bolus is crucial in obtaining diagnostic quality images. The technique has to be optimized for the CT scanner being used. Scanning is done from caudal to cranial direction to minimize streak artifact from the superior vena cava and to avoid breathing motion artifact from the diaphragm, during the latter part of the scan, if the patient cannot breath-hold.

Using single detector CT, the patient is scanned from the domes of the diaphragm to the top of the aortic arch in a single breath-hold following a scan delay of 25 seconds. Images are obtained at 2.5 mm to 3 mm collimation and reconstructed at 1.5 to 2 mm intervals. Using the 4 row multidetector CT scanner, because of the scanner speed, the entire chest can be scanned in 17 to 22 seconds, following a scan delay of 20 seconds at 1.25 mm collimation with images reconstructed at 0.625 mm intervals. Using 8-row detector multidetector CT the scan time is reduced again by half and on 16-row detector multidetector CT, to one-fourth, or approximately 5 seconds—of great benefit in patients with shortness of breath.

CTPA is interpreted on a workstation and read using a scrolling mode with altering of the window level and width dynamically for optimal evaluation of the pulmonary arteries. The scrolling mode is used to pan through the main, lobar, segmental, and subsegmental pulmonary arteries; hence, it is extremely important to be familiar with the pulmonary arterial anatomy.

Acute PE is principally diagnosed by visualizing a low attenuation filling defect within a well-opacified pulmonary artery (Figs. 21.6 and21.7). Other CT findings of acute PE are listed in Table 21.4. Some of these signs include the “railway track” sign (Fig. 21.8D), the vessel cutoff sign, and the rim sign (Fig. 21.8C), where there is a filling defect due to thrombus with a rim of contrast around it. If there is occlusive thrombus, the corresponding artery may be larger and completely filled with low attenuation thrombus. In the case of nonocclusive thrombus, the rim sign may be seen or low attenuation thrombus can be seen in the center of the artery as a nonadherent thrombus or occasionally at the periphery. Ancillary signs of PE, although nonspecific by themselves, can be helpful in case of subtle thrombus. These can manifest as small pleural effusions, atelectasis, or pulmonary infarct distal to a PE (Fig. 21.8), oligemia or mosaic attenuation (Fig. 21.9) due to differential perfusion, and, in case of massive PE, signs of right heart strain with enlargement of the right ventricle and straightening of the interventricular septum.

Intraluminal filling defects on CT are very specific for the diagnosis of PE.

The source of thrombus can occasionally be seen on the chest CT, such as in the superior vena cava, brachiocephalic veins, other neck veins, or the right atrium (Fig. 21.10). Pulmonary infarcts appear as triangular areas with a broad base in contact with the pleural surface and apex directed centrally, with a feeding vessel at the apex. Classic pulmonary infarcts do not enhance, whereas atelectasis or consolidation due to pneumonia often enhances. An advantage of CT is its capability of detecting thoracic abnormalities that mimic signs and symptoms of PE, aiding appropriate and immediate management of these patients (23). These abnormalities manifest as pleural, parenchymal, pericardial, or chest wall disease, seen in up to 40% to 70% of patients with suspected PE, such as pneumonia or abscess (Fig. 21.11), tumor (Fig. 21.12), septic emboli, malignant or nonmalignant pleural effusions, pericardial effusion (Fig. 21.13), pneumothorax, and chest wall tumors.

The neck, extremity, and mediastinal veins should all be examined on pulmonary embolism CTs for the source of emboli.

Pitfalls in the diagnosis of PE on CT are listed in Table 21.5. It is important to use the scrolling mode, so as not to mistake a vein for an artery, an adjacent perihilar node for an arterial filling defect, or mucoid-filled dilated bronchi for an arterial filling defect. Poor contrast bolus causing inadequate opacification of the pulmonary arteries, extensive breathing motion artifact, cardiac motion artifact, low signal-to-noise ratio due to large patient size, and artifact from tubes and lines in critically ill patients can sometimes pose a challenge in the evaluation of PE in these patients (24,25,26).

Figure 21.6 Acute massive pulmonary embolism. Computed tomography demonstrates a large central thrombus in right main pulmonary artery (arrow). Left lobar pulmonary embolism is also noted (arrowheads).

Figure 21.7 Acute pulmonary embolism. Computed tomography demonstrates (A) saddle embolus (arrow)(B) central pulmonary embolism in right main pulmonary artery (arrow), and (C) bilateral lobar pulmonary embolism, with rim sign demonstrated (arrows).Note lobar pulmonary embolism in the left lower lobe (arrowhead) and (D) segmental pulmonary embolism (arrows). Tram track sign is seen in the middle lobe pulmonary artery (curved arrow)E. Subsegmental pulmonary emboli are also demonstrated (arrows).

Table 21.4: Findings of Acute Pulmonary Embolism on Computed Tomography

Direct

Indirect

Clot

Pulmonary infarct

Railway track sign

Large pulmonary artery

Vessel cutoff

Pleural effusion

Rim sign

Atelectasis
Mosaic attenuation

Figure 21.8 Pulmonary infarct. Computed tomography demonstrating right wedge-shaped peripheral pulmonary infarct (arrow) and somewhat rounded left lower lobe pulmonary infarct (arrowheads) secondary to pulmonary embolism.

Figure 21.9 Mosaic attenuation. Computed tomography demonstrating hypo- and hyperattenuated lung parenchyma.

Figure 21.10 Brachiocephalic vein thrombosis. Computed tomography demonstrates a filling defect (arrow) representing thrombus in the right brachiocephalic vein surrounding a venous catheter.

Figure 21.11 Conditions clinically mimicking acute pulmonary embolism. A. Computed tomography demonstrates an infected thrombus(arrow) (positive blood cultures), pericardial effusion (arrowheads) and (B) right lower lobe lung abscess (white arrow) with an adjacent empyema (short arrows), and a right atrial myxoma (curved arrow).

Figure 21.12 Conditions clinically mimicking acute pulmonary embolism. A. Axial computed tomography and (B) sagittal computed tomography reformat, demonstrate left hilar abnormal soft tissue (arrows) and enlarged nodes surrounding the left pulmonary artery (LPA) and its branches, secondary to bronchogenic carcinoma.

Figure 21.13 Conditions clinically mimicking acute pulmonary embolism. Computed tomography demonstrating a large pericardial effusion (asterisk) in a patient later diagnosed with systemic lupus erythematosus.

Table 21.5: Pitfalls in the Diagnosis of Acute Pulmonary Embolism on Computed Tomography

Pulmonary Embolism Mimics

Limitations in Accurate Diagnosis

Partial volume averaging

Image noise in large patients

Perihilar/bronchopulmonary lymph nodes

Respiratory motion artifact

Mucoid impacted bronchi

Cardiac motion artifact

Mistaking a pulmonary vein for an artery

Streak artifact from lines and tubes

Electron Beam Computed Tomography

Electron beam CT allows scanning during maximal opacification of vessels with the main advantage of very short aquisition times in the order of 14 to 17 seconds, with subsequent decreased respiratory and cardiac motion artifacts. Breath-holding is not mandatory, and a smaller amount of contrast material is administered peripherally (80 to 120 mL). Images are performed at 3 to 6 mm collimation and reconstructed at 3 to 1.5 mm collimation (27,28,29). Image interpretation is similar to that described for helical CT. With thin-section helical scanners there is no statistically significant difference in the number of analyzable pulmonary arteries; electron beam CT has a minor advantage in evaluation of the paracardiac arteries.

Computed Tomography Venography

With the advent of faster multidetector CT scanners, it has been possible to evaluate the pelvic and lower extremity veins, allowing evaluation of the pulmonary emboli and the cause thereof, DVT in the lower extremities, with a single study.

After a scan delay of 3 minutes from the intravenous injection given for CTPA, the patient is scanned from the caudad to cranial direction from the level of the tibial plateaus to the iliac crests at 7.5 mm collimation. Images are reconstructed at 3.75 mm collimation and are interpreted at the workstation, using a scrolling mode. DVT is diagnosed when there is an occlusive or nonocclusive filling defect (Figs. 21.14 and 21.15). Venous enhancement of more than 80 Hu is needed to identify DVT. Reasons that optimal venous enhancement may not be obtained include arterial inflow problems, particularly peripheral vascular occlusive disease, hypotension, and hemodilution. Orthopedic hardware may cause extensive artifact, limiting evaluation of segments of veins. Several investigators have demonstrated a high sensitivity and specificity in the detection of DVT, using venous sonography as the reference test; the accuracy for CT venography to detect DVT in the infrapopliteal vessels is not yet known (30,31). An advantage of CT is the ability to evaluate the iliac vessels and the inferior vena cava, which are difficult to evaluate with sonography particularly in large patients (Fig. 21.21).

Helical CT venography, combined with CTPA, is highly accurate for the diagnosis of DVT from the inferior vena cava through the popliteal veins.

Magnetic Resonance Imaging

MRI is useful in the evaluation of suspected PE, particularly in patients allergic to iodinated contrast medium, in children, and in pregnant women, because it does not involve ionizing radiation. Intravenous gadolinium is used as a contrast agent. With evolving scanners and techniques, there is no uniform single MRI protocol. PE is detected as a flow void, and the remainder of the normal signal from flowing blood is processed to obtain two-dimensional and three-dimensional images (Figs. 21.16 and 21.17) (32,33).

Multiplanar reformatting can help evaluation, as in CT. MRI, like CT, allows direct visualization of emboli. It is useful in the detection of central and segmental PE, whereas at the subsegmental level accuracy is less well evaluated. Newer and faster MR scanners and recirculating MR contrast agents may improve MRI accuracy. Furthermore, MRI perfusion techniques may assist in the evaluation of PE, especially in the case of small acute emboli or in the evaluation of thromboembolic disease leading to pulmonary arterial hypertension (34). Defects in pulmonary perfusion are comparable with perfusion defects on V/Q scan in cases of PE. Ventilation scanning is also now possible with MRI (35).

Figure 21.14 Acute deep venous thrombosis. Computed tomography demonstrates filling defects of acute deep vein thrombosis in (A)bilateral common iliac veins (arrows)(B) bilateral external iliac veins (arrows)(C) right common femoral vein (arrow), and (D) right calf vein (arrow).

MR venography has been shown to be comparable with or even better than ultrasound and conventional venography for the detection of DVT, and is particularly useful in the evaluation of patients in whom sonography is not possible. Like CT, it allows direct visualization of clot in the pelvis and lower extremity veins but without the administration of contrast. Gradient-echo and time-of-flight images demonstrate low signal clot occluding a vein or low signal clot surrounded by high signal flowing blood.

Figure 21.15 Acute popliteal venous thrombosis. Computed tomography demonstrates a filling defect in the left popliteal vein, with the rim sign (arrow).

Figure 21.16 Normal magnetic resonance angiography of the pulmonary arteries (PA).

Chronic Pulmonary Embolism

Chronic PE can be difficult to diagnose and can be a cause of pulmonary hypertension. The imaging findings of chronic PE represent recanalization of the arterial lumen previously occluded by an acute central clot. As such, it appears as webs, stenoses, or peripheral thrombi that may or may not be calcified. The most specific finding is low attenuation thrombus at the periphery of the vessel or adherent to the vessel wall, and it may be irregular and may contain calcium. Chronic PE can lead to pulmonary hypertension. Enlarged and tortuous central pulmonary arteries with pruning of the peripheral pulmonary arteries indicate pulmonary hypertension. Mosaic attenuation can also be seen.

Figure 21.17 Acute pulmonary embolism. Magnetic resonance angiography demonstrates filling defect (arrow) compatible with pulmonary embolism in the (A) right and (B) left main pulmonary arteries. (Courtesy of Dr. Ruth Carlos, Ann Arbor, MI.)

Radiology in the Diagnosis of Chronic Pulmonary Embolism

Chest Radiograph

The chest radiograph may be normal in early chronic thromboembolic disease. Enlarged central pulmonary arteries, with narrow caliber peripheral arteries, peripheral oligemia, and right ventricular enlargement, can result as a consequence of recurrent chronic PE (Fig. 21.18).

Ventilation-Perfusion Scanning

The findings are similar to those of acute PE. Multiple mismatched perfusion defects are diagnostic of multiple segmental emboli. A high proportion of indeterminate/intermediate probability V/Q scans occur in patients with chronic PE.

Pulmonary Angiography

Angiographic signs of chronic PE are the presence of eccentric mural thrombi, webs or bands, intimal irregularities, varying caliber of the vessels (Fig. 21.19), abrupt vessel narrowing, pouch defects, or complete obstruction of the vessels. Poststenotic dilation can be seen distal to a narrowing or web.

Computed Tomography

CT is the imaging modality of choice in the evaluation of patients with PAH and suspected CTEPH (36,37). CTPA may demonstrate eccentric thrombus adjacent to a vessel wall in the form of crescentic mural-adherent thrombus (Fig. 21.20). The thrombus may be retracted, or there may be recanalization of thrombus with contrast seen traversing the intraluminal filling defect. Arterial webs and narrowing (Figs. 21.21,21.22, and 21.23), irregular caliber vessels with abrupt narrowing of the arteries, or complete occlusion at the level of the narrowing can also be seen (38,39). Calcification is seen in approximately 10% of chronic central thrombi (Figs. 21.18 and 21.24). Secondary signs include irregular or nodular arterial walls, abrupt narrowing of arteries, or abrupt cutoff of peripheral segmental arteries. A marked variation in size of segmental vessels is more specific for chronic pulmonary thromboembolism than mosaic attenuation.

Webs, wall thickening, and stenosis are the hallmarks of chronic PE on both CT and catheter angiography.

Figure 21.18 Calcified chronic pulmonary embolism. A. Chest radiograph and (B) computed tomography demonstrating calcification in the left pulmonary artery, compatible with calcified thrombus (arrow).

Figure 21.19 Chronic pulmonary embolism with stenosis. Selective right pulmonary angiogram demonstrating segmental stenosis of the right upper lobe pulmonary artery (arrow). (Courtesy of Dr. K. Cho, Ann Arbor, MI.)

Figure 21.20 Chronic pulmonary embolism with peripheral filling defect. Computed tomography demonstrates a crescentic filling defect in left lower lobe pulmonary artery (arrows).

Figure 21.21 Chronic pulmonary embolism with web. Computed tomography demonstrates a linear filling defect in left lower lobe pulmonary artery (arrow).

A mosaic perfusion pattern to the lungs on CT, described as patchy areas of decreased attenuation interspersed with areas of increased or normal attenuation due to regional differences in blood flow (Fig. 21.9), may occur with CTEPH (40). The areas of hypoattenuation represent decreased perfusion and areas of hyperattenuation represent perfused or hyperperfused lung. However, sometimes it is difficult to differentiate between primary vascular disease, small airways disease, and pulmonary parenchymal disease as the cause of mosaic pattern. The number and caliber of the vessels helps to distinguish between these etiologies. In pulmonary parenchymal disease, the vessel caliber is uniform throughout areas of varying attenuation, whereas in the other two the vessels are decreased in caliber in the hypoattenuated areas. Airway and primary vascular disease can be differentiated by air trapping found on expiratory images in patients with small airways disease but not in patients with vascular disease. High resolution CT may demonstrate cylindrical airway dilatation adjacent to stenotic or obstructed pulmonary arteries in up to two-thirds of patients (41).

Mosaic perfusion is a lung finding of chronic PE on CT.

Figure 21.22 Chronic pulmonary embolism with recanalization of thrombus. Computed tomography demonstrates central contrast within thrombus (arrow) in the right descending pulmonary artery.

Figure 21.23 Chronic pulmonary embolism with calcified thrombus. Computed tomography demonstrates a low attenuation thrombus(arrowheads) with calcification.

Figure 21.24 Septic emboli. Computed tomography demonstrates (A) bilateral peripheral nodules with peripheral enhancement(arrows)(B) bilateral peripheral wedge-shaped abnormalities, and (C) thrombus in the left subclavian vein (arrow) (infected porta catheter removed was the source of the septic emboli).

Magnetic Resonance Imaging

MR angiographic features are similar to CT and conventional angiography (42). The peripheral arteries in patients with chronic PE are of varying caliber. MR images may be reconstructed in two or three dimensions, producing image quality similar to conventional angiography, now possible with multidetector CT. The main advantage of MRI is the ability to provide quantitative measurements of pulmonary perfusion, flow measurements in the pulmonary arteries, and quantitative analyses of the ejection fraction of the right ventricle before and after treatment. The disadvantages are poor spatial resolution, breathing motion artifacts, longer imaging times, and less availability. It is particularly useful in patients allergic to iodinated contrast media.

Septic Pulmonary Embolism

Septic emboli often arise from infected central venous catheters or occur in patients with intravenous drug abuse due to peripheral septic thrombophlebitis (Fig. 21.24) or tricuspid valve endocarditis (43). Occasionally, infection from the pharynx or parapharyngeal space can extend into the internal jugular vein, leading to septic emboli or Lemierre syndrome (Fig. 21.25). Other causes include infection in patients with immunologic deficiencies, skin infection, infected arm and pelvic veins, and infected arteriovenous fistulas. Blood cultures in these patients are often positive for Staphylococcus aureus and less commonly Streptococcus. Patients present with fever, cough, and hemoptysis.

Figure 21.25 Septic emboli. A. Computed tomography demonstrates bilateral cavitary septic emboli (arrows)B. Computed tomography of the neck in the same patient demonstrates a left parapharyngeal abscess (arrow), the source of the septic emboli, and thrombus in the left internal jugular vein (arrowhead).

Septic emboli on chest radiograph and CT manifest as multiple, ill-defined, wedge-shaped, or round peripheral nodules, which may be unilateral or bilateral and can be asymmetric (Figs. 21.24 and 21.25). They can come and go, with new lesions appearing and others resolving due to showering of infected foci into the pulmonary artery circulation over time. As they evolve, they may become better defined, smaller, and demonstrate cavitation (Fig. 21.25). Extension into the pleural space can occur, resulting in an empyema. On CT, vessels may be associated with the nodules. The feeding vessel sign, different stages of cavitation and intracavitary debris, and peripheral enhancement may be seen. Septic emboli can result in pulmonary infarction, seen as a triangular wedged-shaped opacity that demonstrates peripheral enhancement due to blood flow from bronchial arteries and central low attenuation or nonenhancement.

Multiple, new, peripheral, ill-defined nodules, with or without cavitation, should raise suspicion for septic embolism.

Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is defined as systolic pulmonary artery pressure above 30 mm Hg or mean value of 18 mm Hg. The most common presenting feature of patients with pulmonary hypertension is dyspnea. Patients may have other symptoms, such as decreased exercise tolerance, fatigue, chest pain, syncope, cyanosis, and peripheral edema. The clinical diagnosis is based on a combination of physical signs, echocardiography, and radiology, with right heart catheterization being the definitive diagnostic test. The etiologies of pulmonary hypertension are listed in Table 21.6. Pulmonary hypertension may be either primary or secondary in etiology, with diseases grouped into a precapillary and postcapillary classification.

Primary pulmonary hypertension is rare and is idiopathic in etiology, occurring three times more commonly in young or middle-aged women than in men. It has an incidence of approximately one per million. Patients present with dyspnea, fatigue, angina, syncope, and cor pulmonale. Secondary precapillary causes of PAH include chronic thromboembolic disease, interstitial lung disease and obstructive pulmonary parenchymal disease, anorexigenic drugs, congenital heart disease (Fig. 21.26), and human immunodeficiency virus infection.

Table 21.6: Etiologies of Pulmonary Hypertension

Precapillary

Postcapillary

Primary Vascular Disease

Pleuropulmonary Disease

Alveolar Hypoventilation

Cardiac Disease

Pulmonary Venous Disease

Primary pulmonary hypertension
Pulmonary thromboembolic disease
Multiple pulmonary artery stenoses
Pulmonary vasculitis
Pulmonary capillary hemangiomatosis
Immunologic (SLE, scleroderma)

Emphysema
Diffuse interstitial lung disease
Bronchiectasis (cystic fibrosis)
Post-pneumonectomy
Fibrothorax
Chest wall deformity

Neuromuscular disease
Obesity
Obstructive sleep apnea
Chronic upper airways obstruction in children

Left ventricular failure
Left atrial myxoma/thrombus
Cor triatriatum
Mitral valve disease

Pulmonary veno-occlusive disease
Anomalous pulmonary venous drainage
Fibrosing mediastinitis
Congenital stenoses of pulmonary veins
Thrombosis
Neoplasms

SLE, systemic lupus erythematosus.

Figure 21.26 Primary pulmonary arterial hypertension. A. Chest radiograph demonstrates enlarged bilateral central pulmonary arteries and attenuated peripheral pulmonary vasculature. B and C. Right and left pulmonary angiograms demonstrate enlarged central pulmonary arteries with tortuous distal pulmonary arteries.

Pulmonary veno-occlusive disease is a rare postcapillary cause of PAH in which webs due to recanalized thrombus and intimal fibrosis are seen in the pulmonary veins. Before 1990, the diagnosis was often made postmortem but now is more frequently made antemortem by recognizing the various modes of presentation and with the help of high resolution CT. The diagnosis is usually made by excluding other causes of pulmonary hypertension, with the findings of interstitial edema and ground glass opacity on chest radiograph or high resolution CT. In capillary hemangiomatosis, nodular collections of thin-walled capillaries invade the pulmonary arteries, veins, and bronchioles; it is considered a subset of pulmonary veno-occlusive disease by some authors. Less than 1% of patients with chronic liver failure may also develop PAH, which may be secondary to circulating vasoactive substances that the liver fails to metabolize (44).

Pulmonary hypertension is a significant cause of morbidity and mortality but is a potentially treatable condition. Therapy ranges from medical treatment with vasodilators to surgical treatment with lung or combined heart–lung transplant. The treatment of choice for CTEPH is pulmonary endarterectomy. In cases of suspected CTEPH, pulmonary angiography or CT may be performed, as described earlier.

Radiology in the Diagnosis of Pulmonary Hypertension

Chest Radiograph

The classic radiographic findings of advanced PAH are enlargement of the central pulmonary arteries that may be tortuous with pruning of the peripheral arteries, peripheral oligemia, and right ventricular enlargement (Fig. 21.27) (45). Calcification of the central pulmonary arteries can be seen in severe chronic PAH. A completely normal CXR film speaks against the diagnosis of primary pulmonary hypertension; the National Institutes of Health registry showed that only 6% of patients with primary PAH have a normal chest radiograph. There is controversy regarding the exact measurement of the vessel diameter and degree of PAH, because such measurements vary with magnification, patient positioning, and patient size. The upper limit of normal for the right interlobar pulmonary artery on the frontal chest radiograph is 15 mm or less in women and 16 mm or less in men. For the left descending pulmonary artery, the upper limit of normal on the lateral chest radiograph is 17 mm (46).

The upper limit of normal for the right interlobar pulmonary artery is 15 mm in women and 16 mm in men on the frontal chest radiograph.

The upper limit of normal for the right interlobar pulmonary artery on the lateral radiograph is 16 mm.

Echocardiography

PAH is usually evaluated noninvasively with echocardiography, allowing assessment of cardiac chamber size, valve function, wall thickness and function, the detection of intracardiac shunts, and an estimate of pulmonary arterial pressure. The latter is estimated from right ventricular peak systolic pressure. In addition to pulmonary arterial enlargement, the right atrium and ventricle may be enlarged, with accompanying tricuspid valve regurgitation. The superior and inferior vena cava may also be enlarged. The use of microbubbles in the form of an agitated saline bolus administered intravenously aids in the detection of intracardiac shunts. Stress echocardiography can be performed to evaluate the dynamic response of the heart to physical or pharmacologic stress (47).

Figure 21.27 Congenital heart disease as a cause of pulmonary hypertension. A. Computed tomography demonstrates an atrial septal defect (arrow) and a (B) ventricular septal defect (arrow).

Ventilation-Perfusion Scanning

The findings are similar to those of chronic thromboembolic disease causing PAH. Multiple mismatched perfusion defects are diagnostic of multiple segmental emboli; however, there are a high number of indeterminate/intermediate probability V/Q scans (48). In the absence of CTEPH, the V/Q scan may be normal or low probability in patients with PAH.

Computed Tomography

CT is the imaging modality of choice in the evaluation of patients with PAH and suspected CTEPH, evaluating both the lung parenchyma with high resolution CT technique and pulmonary artery with CTPA, discussed earlier in the chapter. Multidetector CT scanners are also useful in the evaluation of cardiac disease (Fig. 21.27). CT in primary pulmonary hypertension demonstrates marked dilatation of the central pulmonary arteries with abrupt tapering and small caliber peripheral vessels with resultant oligemia or hypoattenuation of the lungs. The upper limit of normal of the main pulmonary artery on CT is 29 mm, above which PAH should be suggested (49). Mosaic attenuation may be present. The CT findings of CTEPH were covered earlier in this chapter. Pericardial effusions are commonly seen in patients with PAH and are usually small to moderate in size. High resolution CT is useful in the evaluation of the lung parenchyma in patients undergoing intravenous prostacyclin therapy for pulmonary hypertension. Ground glass attenuation, centrilobular nodules, and septal lines may be associated with a high risk of treatment failure (50).

In pulmonary veno-occlusive disease, the imaging findings are those of pulmonary hypertension and edema. The central pulmonary veins may also be very small, and there is often gravity-dependent ground glass attenuation, thickened interlobular septa, pleural effusions, and a normal sized left atrium (51). Centrilobular nodules are often seen with pulmonary capillary hemangiomatosis.

Magnetic Resonance Imaging

MR angiographic features in primary pulmonary hypertension are similar to those on CT and conventional angiography. The peripheral vessels in primary pulmonary hypertension may be uniform in caliber, whereas those in patients with chronic PE are of varying caliber.

Pulmonary Tumor Embolism

Pulmonary tumor embolism is rare in clinical practice but is often seen at autopsy. Occasionally, it may be a presenting feature of malignancy. Patients may present with pleuritic chest pain, dyspnea, cough, hemoptysis, and weight loss. Primary tumors that are associated with pulmonary tumor embolism are bronchoalveolar cell carcinoma; carcinoma of the breast, kidney (Fig. 21.28), and stomach, hepatoma; and choriocarcinoma. Tumor emboli are clumps of malignant cells that can partially or completely occlude pulmonary arteries. On CT, MRI, and angiography they appear similar to acute venous thromboemboli. Dilated and beaded arteries are also seen (52,53). Because these are rarely diagnosed antemortem, the response to chemotherapy has not been tested. High mortality is noted in these patients.

Beaded and/or thick-walled pulmonary arteries should raise suspicion of pulmonary tumor embolism.

Figure 21.28 Pulmonary tumor embolism. A. Computed tomography demonstrates tumor embolism in the right pulmonary artery(arrow) from (B) right renal cell carcinoma (arrows).

Pulmonary Arteriovenous Malformation

Pulmonary AVMs represent an abnormal vascular connection between the pulmonary arteries and pulmonary veins, with no intervening capillary network. They can range from microscopic communications to large malformations, with a large single feeding vessel and draining vein, or complex malformations, with multiple feeding vessels and draining veins. Pulmonary AVMs are right-to-left shunts that may manifest as cyanosis, polycythemia, stroke, brain abscess, or paradoxical emboli. More commonly they present as an incidental finding on a chest radiograph or CT. Hemoptysis or hemothorax are uncommon (9%). Pulmonary AVMs can be single or multiple. Approximately 60% of patients with multiple pulmonary AVMs have hereditary hemorrhagic telangiectasia, also known as Osler-Weber-Rendu syndrome (Chapter 13). Pulmonary AVMs are single in 60% to 70% of cases and multiple in 30%. They are more common in the lower lobes than in the upper lobes.

Pulmonary AVMs are commonly part of Osler-Weber-Rendu syndrome.

On chest radiography, AVMs are often seen as well-defined nodules, which are somewhat lobulated and range from 1 cm to several centimeters in size. They are often associated with a feeding artery originating at the hilum and a draining vein coursing toward the left atrium. Although most AVMs have a single feeding artery and draining vein, approximately 20% have two or more feeding vessels. The characteristic appearance of lobulated enhancing nodules with a draining vein and a feeding artery or a serpiginous mass of vessels is diagnostic of AVMs on intravenous contrast-enhanced CT (Fig. 21.29) (54,55). Calcification is occasionally seen in a nodule due to the presence of a phlebolith. CT is especially useful for posttherapy follow-up and may demonstrate persistence of a lesion or enlarging lesions. Three-dimensional CT is particularly useful in delineating the number, size, and exact location of the AVM and has been found to be comparable with pulmonary angiography. Nonetheless, pulmonary angiography is the definitive diagnostic test and is often performed for absolute confirmation, exact delineation of the size, location, and number of AVMs, and the number of feeding arteries and draining veins. Pulmonary angiography also aids therapeutic intervention, such as embolization. Treatment of AVMs reduces the symptoms of hypoxemia and reduces the risks of paradoxical emboli which may present clinically as a brain abscess.

Most pulmonary AVMs have a single feeding artery and a single draining vein.

Figure 21.29 Arteriovenous malformations. Computed tomography demonstrating bilateral arteriovenous malformations (arrows), with feeding vessels and draining veins.

Pulmonary Artery Stenosis

Stenosis of the pulmonary artery may be single or multiple (Table 21.7). Williams-Beuren syndrome is a rare congenital disorder with pulmonary artery stenosis, mental retardation, and peculiar facies. Central pulmonary artery stenosis is often associated with cardiovascular abnormalities and congenital heart disease; the latter is discussed in Chapter 19. Extrinsic pulmonary artery compression is usually secondary to an adjacent mediastinal or hilar neoplasm (Fig. 21.30) or fibrosing mediastinitis (Fig. 21.31). Patients may present with signs and symptoms of PE. Patients with peripheral pulmonary artery stenosis may demonstrate a loud second heart sound and a systolic murmur.

On chest radiograph, the pulmonary vasculature may be diminished distal to a pulmonary artery stenosis, or there may be poststenotic dilatation, especially if pulmonary artery stenosis is the only abnormality. CT readily demonstrates pulmonary artery stenosis, especially with the reconstruction capability of multidetector CT. CT is particularly useful in the evaluation of the causes of compression of the pulmonary arteries. Selective pulmonary angiography may be useful in the detailed evaluation of the stenosis and the distal vasculature.

Pulmonary Artery Aneurysms and Pseudoaneurysms

Aneurysms of the pulmonary artery are rare and may be idiopathic, congenital, or secondary, as listed in Table 21.8. Congenital aneurysms are commonly proximal and associated with pulmonary valve stenosis. Hughes-Stovin syndrome is a rare disorder in which small and large aneurysms of the pulmonary arteries are accompanied by thrombosis of the dural sinuses and peripheral veins; it may be associated with Behçet disease. Larger aneurysms are usually seen secondary to atherosclerosis, thrombosis, or cystic medial necrosis.

Table 21.7: Etiologies of Pulmonary Artery Stenosis

Congenital

Extrinsic/Pulmonary Artery Compression

Associated with congenital heart disease

Ehlers-Danlos syndrome

William-Beuren syndrome

Fibrosing mediastinitis

Down syndrome
Ehlers-Danlos syndrome

Sequela of radiation treatment

Figure 21.30 Pulmonary artery stenosis. Computed tomography demonstrates extrinsic compression of the right main pulmonary artery(arrowheads) from large central tumor (T) and an associated pericardial effusion (arrows).

Figure 21.31 Pulmonary artery stenosis. Computed tomography demonstrates stenoses of the (A) right (arrow) and (B) left (long arrow) pulmonary arteries from surrounding abnormal soft tissue secondary to mediastinal fibrosis.

Table 21.8: Etiologies of Pulmonary Artery Aneurysms

Congenital

Idiopathic

Secondary

Associated with pulmonary valve stenosis and ASD

Hughes-Stovin syndrome
Williams syndrome

Pulmonary hypertension
Trauma
Infection—syphilis, TB, mycosis
Marfan syndrome
Behçet disease
Sequela of pulmonary parenchymal disease

ASD, atrial septal defect; TB, tuberculosis.

Figure 21.32 Pulmonary artery aneurysm. A. Chest radiograph demonstrates aneurysm of the right descending pulmonary artery(arrows) secondary to pulmonary hypertension from sarcoidosis. Note bilateral mid lung interstitial linear opacities. B. Selective right pulmonary angiogram demonstrates the aneurysm (arrow) of the right descending pulmonary artery.

Pulmonary aneurysms are often asymptomatic. They may present with signs and symptoms secondary to complications, such as rupture leading to hemoptysis or encroachment onto a bronchus.

On chest radiograph, a peripheral pulmonary artery aneurysm may present as a pulmonary nodule ranging in size from a few millimeters to a few centimeters. There may be surrounding hemorrhage noted as airspace disease. Hence, this could be easily overlooked. Centrally, it may appear as a large pulmonary artery (Fig. 21.32). CT and MRI both demonstrate central and peripheral pulmonary artery aneurysms and any internal thrombus well (Fig. 21.33). Calcification of the walls of the aneurysm may be seen (Fig. 21.34). The most valuable role of CT and MRI is to differentiate aneurysms from tumor. Angiography plays a dual role in both diagnosis (Fig. 21.32) and treatment of pulmonary aneurysms in the form of embolization with coils or balloons.

Pulmonary pseudoaneurysms are rare, the etiologies include trauma (Fig. 21.35), pneumonitis with consequent pulmonary vascular erosion (tuberculosis, mycotic) (Fig. 21.36), vasculitis such as Behçet syndrome, septic arterial seeding, and secondary to trauma. When an intensive care unit patient develops hemoptysis or a central enlarging mass with or without adjacent airspace disease on a chest radiograph, a Swan-Ganz catheter injury should be considered (56). The mass could represent a pulmonary artery pseudoaneurysm. When the pseudoaneurysm is peripheral, it can be treated with embolization, but when the pseudoaneurysm is central, surgical repair; allowing preservation of flow to the lung is preferred.

Pulmonary Artery Aplasia and Hypoplasia

Pulmonary artery aplasia can be isolated or associated with hypogenetic lung or hypoplastic lung (Fig. 21.37). There are few if any clinical problems associated with isolated pulmonary artery aplasia. The affected lung is normal in size or small, and there is marked decrease in pulmonary vasculature. The normal lung can demonstrate increased vasculature, as the cardiac output is diverted to that side. On chest radiograph, the affected lung is hyperlucent and may be small. Scintigraphy demonstrates normal ventilation but total absence of perfusion. CT and MRI may demonstrate absence of pulmonary artery and systemic to pulmonary collaterals (Fig. 21.37). Pulmonary artery hypoplasia can also occur secondary to radiation therapy (Fig. 21.38).

Figure 21.33 Pulmonary artery aneurysm. Computed tomography demonstrating pulmonary artery aneurysm (arrow) in a patient with congenital heart disease.

Figure 21.34 Pulmonary artery aneurysm. Computed tomography demonstrates peripherally calcified pulmonary artery aneurysm(arrows).

In pulmonary artery aplasia and hypoplasia, the pulmonary artery is absent or small and the lung small or normal in size but normally ventilated.

Swyer-James syndrome (Macleod syndrome) can mimic pulmonary artery hypoplasia or aplasia. It often occurs secondary to a viral infection in the immature developing lung that results in obliterative bronchiolitis. Pathologically, there may be the presence of bronchitis, bronchiolitis, constrictive obliterative bronchiolitis, and occasionally emphysema.

 

Patients are usually asymptomatic and detected incidentally. Less commonly, they present with recurrent respiratory infections and exertional dyspnea. On chest radiography, the abnormal lung is hyperlucent (Fig. 21.39), with diminished vasculature. Usually, an entire lung is affected, although there may be sparing of a segment or two or even patchy involvement of the opposite side. The pulmonary arteries are hypoplastic and reduced in number and caliber. The findings are well demonstrated on CT, which more commonly reveals the bilateral abnormalities. Air trapping is seen in the affected lung. Scintigraphy demonstrates decreased perfusion and abnormal ventilation. MRI demonstrates a small pulmonary artery on the affected side with decreased vasculature (Fig. 21.39).

Figure 21.35 Pulmonary artery pseudoaneurysm. Chest radiograph demonstrates a right costophrenic angle smooth mass (arrows), secondary to Swan-Ganz catheter insertion, new from a prior normal chest radiograph and confirmed on computed tomography and angiography.

Figure 21.36 Mycotic pulmonary artery pseudoaneurysm. A. Computed tomography demonstrates an enhancing mass in the left mid-chest of almost equal attenuation to the pulmonary arteries, with surrounding low attenuation thrombus (B), confirmed on angiography.

Figure 21.37 Pulmonary artery aplasia. A. Chest computed tomography demonstrates absent left pulmonary artery (arrow) and collateral chest wall vessels (arrowheads)B. Lung windows demonstrating hypoplastic left lung.

In Swyer-James syndrome, the small pulmonary artery is associated with obliterative bronchiolitis and air trapping.

Pulmonary Artery Tumors

Benign and malignant tumors of the pulmonary artery are rare and include leiomyosarcomas and fibrosarcomas. Benign tumors of the pulmonary artery are extremely rare. Almost all tumors arise centrally at the level of the pulmonary valve, pulmonary trunk, or right and left main pulmonary arteries. The artery may be completely occluded by tumor or by the tumor and adjacent thrombus, leading to distal atelectasis and infarction. Hematogenous spread with microscopic and macroscopic metastases is common. More commonly, a mediastinal or central bronchogenic tumor may invade the pulmonary artery.

Figure 21.38 Pulmonary artery hypoplasia. A and B. Posteroanterior and lateral chest radiographs demonstrates diminutive right pulmonary artery (arrows)(C) Computed tomography demonstrates right paramediastinal fibrotic changes secondary to radiation therapy (arrows)D. Pulmonary angiogram demonstrates small right pulmonary artery (arrow) and small peripheral arteries.

Figure 21.39 Swyer-James Syndrome. A. Chest radiograph demonstrates hypolucent left lung. B. Magnetic resonance angiography demonstrates small and decreased pulmonary vasculature on the left side. LPA, left pulmonary artery.

 

On chest radiograph there may be central pulmonary artery enlargement and multiple pulmonary nodules from hematogenous metastases. An intraluminal mass is seen on CT or MRI, sometimes associated with expansion of the pulmonary artery. Tumor may appear very similar to PE but may be differentiated by higher attenuation or finger-like projections or nodules invading adjacent vessel wall or extending into or outside the vessel wall (Fig. 21.40). In addition, tumor may enhance, whereas thrombus does not enhance (57). Angiography similarly demonstrates an intraluminal filling defect that can be indistinguishable from PE and may also demonstrate lobulation of the tumor or tumor blush and tumor vascularity.

Figure 21.40 Pulmonary artery sarcoma. Gadolinium-enhanced magnetic resonance angiography demonstrates an enhancing tumor in the right pulmonary artery (arrows).

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