Additional Discussion:
Pulmonary emboli (PE) can range from small, asymptomatic emboli to massive emboli resulting in sudden death. Emboli may originate from many sources, such as thrombi in veins of the upper extremities or pelvis or the right atrium. However, more than 95% are believed to arise from the lower extremity deep venous thrombosis (DVT).
The three factors that promote thrombosis, and hence PE, are known as Virchow's triad: stasis, vessel wall injury, and systemic hypercoagulability. Risk factors for PE include: age older than 40, malignancy, prolonged immobility, prior DVT, pregnancy, use of oral contraceptives, recent operation, lower extremity injury, and congenital or acquired abnormalities in coagulation.
Dyspnea is the most common symptom and tachypnea is the most common sign. Other frequent manifestations include pleuritic chest pain, apprehension, diaphoresis, hemoptysis, and low grade fever.
Patients with PE often have abnormal EKG findings such as sinus tachycardia or findings of acute right heart strain. They are often hypoxemic, with a widened alveolar-to-arterial oxygen partial pressure (A-a) gradient.
Echocardiography can suggest PE if there is evidence of right ventricular strain or increased pulmonary artery pressure. Occasionally thrombus may be seen echocardiographically.
The majority of patients with PE have abnormal radiographs. The classic named radiographic signs of PE are Westermark's sign (oligemia in a portion of the lung distal to an embolized vessel), Hampton's hump (a peripheral wedge-shaped opacity due to infarction), and Fleischner's sign (a central pulmonary artery enlarged by the embolus). More common, but also more non-specific, radiographic findings are atelectasis and small pleural effusion.
Ventilation-perfusion (VQ) scanning, if normal, has a high negative predictive value and, if high-probability, has a high positive predictive value. Unfortunately, a large proportion of scans are neither normal nor high-probability; even combined with the assessment of the clinical suspicion by a skilled clinician, they are often non-diagnostic, especially when radiographs are abnormal.
Bilateral lower extremity Doppler ultrasound or impedance plethysmography may be performed to detect DVT. DVT requires the same therapy as PE, so its diagnosis can make further investigation for PE unnecessary. However, these tests are usually not positive.
Pulmonary angiography is considered the gold standard for diagnosing PE. Although generally safe and well-tolerated, it is an invasive procedure that requires skilled operators.
With the development of faster CT scanners, much recent research has been directed toward CT pulmonary angiography, a non-invasive and accurate technique. CT has the additional advantage over VQ scanning and conventional angiography of often demonstrating unsuspected lesions that account for symptoms, for example, a pericardial effusion.
There are concerns that pulmonary emboli beyond the segmental pulmonary arteries will not be detected with CT and that the technique is excessively technically demanding and occasionally non-diagnostic. No studies of the size or scope of PIOPED (the study validating VQ scanning) have yet been performed to assess the accuracy of CT angiography. However, because of the versatility of the technique, its performance has become widespread.
Case submitted by: Huong Nguyen, medical student
SUGGESTED READING:
Goldhaber, S.Z., "Pulmonary Embolism" The New England Journal of Medicine, 1998; 339:93-104.
Moser, K. M., "Pulmonary Thromboembolism" in Harrison's Principles of Internal Medicine 1994, pp 1214-20.
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