IS Case 117: Thrombotic Pulmonary Embolism
Imaging Sciences URMC 2008
Publication Date: 2009-05-20
Findings
PA and lateral chest radiographs demonstrate a wedge-shaped opacity of the middle lobe that extends to the lung periphery. A selected axial CT image at the level of the right main pulmonary artery demonstrates filling defects of the distal right main pulmonary artery. There is a corresponding area of consolidative lung parenchymal process of the right middle lobe.
Diagnosis
Thrombotic Pulmonary Embolism
Discussion
Pulmonary embolism (PE) and deep venous thrombosis (DVT) can be recognized as parts of the continuum of one disease entity, venous thromboembolism (VTE). VTE is diagnosed and treated in 260,000 patients in United States per year and more than half of cases are never diagnosed. Therefore as many of 600,000 cases occur annually.
Venous thrombi develop most commonly in the leg veins in patients who display components of Virchow's triad (stasis, hypercoagulability, and intimal injury). Proximal vein thrombi including the popliteal veins and above are more likely to embolize. Emboli originating from axillary and subclavian veins often develop in patients with central venous catheters, particularly those with malignant neoplasms.
The history and physical examination are insensitive and nonspecific for acute pulmonary embolism. The most common symptoms of acute pulmonary embolism is dyspnea, which is often sudden in onset. Pleuritic chest pain and hemoptysis occur more commonly with pulmonary infarction. Other symptoms such as palpitations, cough, anxiety, and lightheadedness may be seen with acute pulmonary embolism, but are nonspecific.
Chest radiography may demonstrate nonspecific findings such as pleural effusion, atelectasis, pulmonary infiltrates, and mild elevation of the hemidiaphragm. Classic findings of pulmonary infarction, such as Hampton hump and decreased vascularity (Westmark sign), are suggestive of the diagnosis but are very infrequent. CT can be used to diagnose both acute and chronic PE, and has replaced VQ scanning at many centers. CT has a sensitivity of 80% to 90% and specificity consistently above 90%. Advantages of CT include the ability to define non-vascular conditions such as lymphadenopathy, lung tumors, emphysema, and other parenchymal abnormalities, as well as pleural and pericardial disease. Another advantage is the rapidity with which the scan can be performed. Disadvantages of CT include poor sensitivity for detecting clots in small vessels, and risk of renal failure in patients with renal insufficiency. V/Q scans can be used to evaluate for PE in patients who cannot have a CT, with a normal perfusion scan essentially excluding PE with a high degree of certainty. However, non-diagnostic V/Q scans are commonly found, and further evaluation is often appropriate.
References
- Tapson VF. Thrombotic pulmonary embolism. IN: Cecil Textbook of Medicine, Goldman L, Ausiello DA (eds.), 23rd ed. Saunders, 2007. [MDConsult]
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