Applied Radiology

Diagnosis

Calcified pulmonary infarcts

Discussion

PE is a common disease in the United States, with 170,000 to 650,000 patients experiencing venous thromboembolism annually. The National Institute of Health estimates that 200,000 to 600,000 patients are hospitalized each year for venous thromboembolism, with approximately 50,000 deaths annually due to PE.

Underdiagnosis of PE is common. A large study in the United States in the mid-1970s estimated that only 29% of patients surviving PE for more than 1 hour had their condition diagnosed and therapy instituted. This is especially unfortunate for a disease in which the mortality is five- to six-fold greater among those patients in whom the diagnosis is missed and the appropriate therapy is not instituted.

Risk factors-One of the greatest risk factors for deep venous thrombosis of the lower extremities and secondary PE is immobilization. An illness such as pneumonia may force an individual to bed rest, resulting in the distinct possibility that a patient may present with PE as a complication of the disease. The most common risk factors for PE include age, previous venous thromboembolism, prolonged immobility or paralysis, malignancy, congestive failure, estrogen use, trauma, pregnancy, obesity, and surgery.

Clinical symptomatology-Symptoms are not rare in PE, but are simply nonspecific. A number of clinical series have reported the incidence of various symptoms and signs among patients proven to have PE. When these studies are reviewed, the lack of specificity of any symptom or sign is apparent. The most common symptoms in a patient with PE are dyspnea, pleuritic chest pain, apprehension, and cough. Unfortunately any or all of these may result from a variety of cardiopulmonary disorders. Can patients with significant PE lack suggested pulmonary symptoms? Unfortunately, the answer is certainly "yes."

Diagnostic study: Chest radiograph-A chest radiograph is an essential part of the work-up of all patients suspected of having PE. Its major value is in eliminating from diagnostic consideration other entities that may mimic the presentation of acute PE, such as pneumothorax. The case presented above demonstrates these focal parenchymal infiltrates. Their wedge shape lends some specificity to the diagnosis of PE; however, this is by no means diagnostic.

Diagnostic study: Ventilation-perfusion lung scan-Ventilation-perfusion lung scanning (V/Q) is the cornerstone test for PE diagnosis, and our understanding of its proper role has increased with well designed studies. The PIOPED trial showed that V/Q lung scan is sensitive and, in some cases, specific for PE. Among patients with PE confirmed by angiography, 97% had abnormal V/Q scans of high, intermediate, or low probability. Of cases of proven PE, 41% had highprobability lung scans. Of all patients with high-probability lung scans, 88% were shown to have PE by a pulmonary angiogram. The level of clinical suspicion combined with the V/Q scan is often enough to raise or lower the possibility of venous thromboembolism sufficiently to make the decision to treat or to not treat.

Diagnostic study: Pulmonary angiography-Pulmonary angiography is considered by many to be the gold standard for the diagnosis of PE, with both sensitivity and specificity > 90%. However, it is an invasive examination and is not without risk, especially since these patients are often acutely ill. This examination can be used when there is clinical concern of PE, yet not enough data to support anticoagulation in an acutely ill patient. In the event of an intermediate-probability V/Q scan, fast CT scanning can be used directly to visualize the pulmonary emboli as a substitute to pulmonary angiography. Initial experience has met with considerable success; however, the true sensitivity and specificity of the examination has yet to be determined in large clinical trials. Its major pitfall is the inability to visualize beyond fourth-order branches of the pulmonary artery and, hence, small distal emboli can be missed.

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