Role of Lower Extremity Ultrasound in Diagnosing Pulmonary Embolism

Diagnostic Approach

The American College of Radiology recommends beginning with clinical probability assessment and D-dimer testing for patients who cannot receive IV contrast; if low clinical probability and negative D-dimer, pulmonary embolism can be safely excluded without imaging 3, 4
For patients with suspected pulmonary embolism who cannot receive IV contrast, lower extremity duplex Doppler ultrasound is recommended as an alternative diagnostic approach, as it can detect deep vein thrombosis which is the source of most pulmonary emboli 1, 2

The American College of Radiology recommends ventilation-perfusion scan as the first-line imaging test for patients with suspected pulmonary embolism who cannot receive IV contrast 4
Lower extremity ultrasound is a valuable alternative or complementary test when ventilation-perfusion scanning is not available or inconclusive 1, 2

A positive finding of deep vein thrombosis on lower extremity ultrasound in a patient with symptoms consistent with pulmonary embolism can be considered evidence for venous thromboembolic disease and may preclude the need for additional diagnostic imaging 2, 5

Patients with obvious signs of deep vein thrombosis, patients with contraindications to CT contrast, pregnant patients, and patients with a history of multiple CTs for pulmonary embolism are candidates for lower extremity ultrasound 1, 2, 5

For patients with intermediate pretest probability and negative CT angiogram, consider lower extremity venous ultrasound as an additional test to exclude venous thromboembolic disease 5
For patients with high pretest probability and negative CT angiogram, additional testing including lower extremity venous ultrasound is recommended 5

Performing lower extremity ultrasound before more advanced imaging can reduce the need for CT pulmonary angiography in approximately 10% of patients 2