Chest
Special FeaturesChronic Pulmonary Emboli and Radiologic Mimics on CT Pulmonary Angiography: A Diagnostic Challenge
Section snippets
Natural History
With treatment, most acute emboli undergo complete resolution. In some patients, for reasons that are unclear, the clot fails to resolve completely and may undergo organization and incorporation into the vessel wall. This may be due to underlying abnormalities in fibrinolysis or possibly recurrent embolism. The resulting thrombus is thought to trigger an arteriopathy in vessels distal to the occluded areas. A compensatory diversion of blood toward the patent vascular bed is also thought to
Alternative Imaging Techniques
The pros and cons of the two commonly used modalities, CTPA and perfusion scanning, are given in Table 1. Perfusion scanning is extremely useful when completely normal, as this excludes CPE by virtue of its high negative predictive value. As an initial test, perfusion scanning has a greater sensitivity than CTPA in diagnosing CPE (96% vs 51%10) with a very good, albeit slightly lower, specificity (90-95% vs 99%10). Of course, perfusion scanning has its own problems with false-positive scans,
Filling Defects in the Arterial Bed
CPE can result in complete occlusion of the vessel lumen. The angiographic appearance has been described as a “pouch defect” because the contrast material has a convex margin within the affected vessel.21 Contraction of the thrombus can cause retraction of the vessel wall, thereby reducing its diameter. On CT scans, the features to look for are (1) sudden truncation of occluded vessels, (2) affected vessels appearing smaller than the patent vessels on the opposite side, and (3) an inability to
Pleural Signs
Pleural effusions are estimated to be present in up to 61% of patients with pulmonary emboli.39 They tend to be small, are commonly unilateral, and generally occupy less than one-third of the involved hemithorax. However, large or bilateral effusions may occur. The fluid is usually an exudate. Loculated effusions have also been described and in some cases have shown improvement with systemic anticoagulant therapy.40
Common Parenchymal Signs
Oligemia distal to occluded vessels causes a redistribution of blood away from the affected areas. These irregularities in perfusion are demonstrated on CT scans as a sharply demarcated, mosaic pattern of attenuation (Fig 6).4 Hypoperfused areas are of low attenuation, with increased attenuation where the vessels have become larger and more prominent. Mosaic attenuation is nonspecific and can be caused by a variety of other pulmonary conditions, including small airways disease and primary
Rare Parenchymal Findings
Aseptic cavitation of large pulmonary infarcts secondary to chronic thrombus (Fig 8) has been occasionally documented in the literature; it is rare and more typically occurs in preexisting areas of infarction.45 Necrosis of infarcted tissue to form a cavity is usually initially aseptic, but secondary bacterial infection or microbial colonization (Fig 9) may occur. Alternatively, infection may be present at the time of cavitation. Cavitation can also be complicated by the formation of a
Radiologic Mimics
There are a myriad of disorders that can mimic CPE radiologically, including a variety of types of thromboembolism (acute thromboembolism, tumor emboli, and in situ thrombus), and inflammatory (arteritis), malignant (primary sarcoma of the pulmonary artery), and developmental causes (proximal interruption of the pulmonary artery), as well as idiopathic pulmonary hypertension itself.
Treatment
The definitive treatment of thromboembolic hypertension is PEA, entailing removal (stripping) of the diseased intima in patients with proximal thromboembolic disease.57 Careful selection of patients for PEA is critical and requires multidisciplinary meetings with medical and surgical specialists and high-quality imaging.58 PEA is not suitable if there is distal or microvascular thromboembolic disease (usually in 20% to 40% of cases), or significant comorbidities, especially COPD or severe left
Conclusions
There are several vascular and parenchymal CT scan features that aid the diagnosis of CPE. Some are less common than others. A high index of suspicion needs to be maintained because the nonspecific clinical presentation and pathologic mimics can create diagnostic dilemmas, potentially delaying definitive treatment. While unusual findings like cavitation of infarcts with or without secondary colonization and bronchopleural fistulae can occur in many other disease pathologies, their presence
Acknowledgments
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
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2013, Clinics in Chest MedicineCitation Excerpt :Chronic thromboembolic disease is bilateral in most patients, with unilateral disease seen in only 3% of 410 patients in one study. If unilateral hypoperfusion of 1 lung is identified with scintigraphy, this should prompt further investigation (CT or MRI) to search for other diseases that may lead to central pulmonary artery occlusion such as pulmonary artery sarcoma, large vessel arteritis, or extrinsic compression of the pulmonary artery from fibrosing mediastinitis or malignancy.71,72 Although CTPA can play a valuable role in the evaluation of patients with CTEPH, 2 caveats must be kept in mind: (1) CTPA alone is not sensitive enough to rule out chronic thromboembolic disease, and (2) the presence of chronic clots on CT does not confirm the diagnosis of CTEPH.
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