Pulmonary embolism occurs in more than 600,000 patients a year in the United States and results in death in approximately one sixth of them. The challenge facing physicians is to identify patients at risk for embolic phenomena and treat them appropriately. Approximately 80 percent of pulmonary emboli arise from the lower extremity. Sonography of the lower extremity is the gold standard for detecting deep vein thrombosis (DVT). A dilemma develops when patients with suspected DVT have a negative sonogram of the lower extremity—should anticoagulation therapy be initiated or should a venogram be performed? Gottlieb and Widjaja sought to determine if additional images were necessary in patients suspected of having DVT whose thigh sonogram was negative.

A retrospective study was performed of all patients with clinical signs or symptoms consistent with DVT who had a negative thigh sonogram. This information was combined with a review of the literature of similar studies. All patients had a follow-up examination six months after the initial presentation. Propagation of DVT from a calf to a thigh and pulmonary emboli were considered adverse outcomes.

In the 146 patients with signs and symptoms of DVT but a negative thigh sonogram, only one pulmonary emboli developed. Of 13 patients who underwent a second sonogram of the thigh for persistent symptoms, one had a positive scan. The review of the literature found that four out of 1,797 patients with negative thigh sonograms developed pulmonary emboli. No deaths from pulmonary emboli occurred in the retrospective study or the studies published in the literature.

The authors conclude that other imaging studies are not necessary in patients who have symptoms consistent with DVT but negative thigh sonograms. Follow-up thigh sonography is indicated in patients whose symptoms are persistent, to detect propagation of calf DVT into the thigh.