Diagnosis of pulmonary embolism.

Recent clinical studies have shed new light on the diagnosis of venous thromboembolism. Pulmonary embolism continues to be difficult to diagnose because the definitive test, pulmonary angiography, is complex and not widely available. However, new knowledge about ventilation perfusion lung scanning and non-invasive leg studies can help to reduce the need for pulmonary angiography. Furthermore, the PIOPED study showed that combining a clinical probability assessment of pulmonary embolism with the lung scan probability more accurately establishes the likelihood of pulmonary embolism. This knowledge can be applied widely to aid the clinician in the diagnosis of pulmonary embolism and deep venous thrombosis. It is now widely accepted that deep vein thrombosis of the lower extremity and pulmonary embolism are two manifestations of the syndrome of venous thromboembolism. Deep vein thrombosis is a progressive process that usually begins in the deep veins of the calf and then propagates directly through the popliteal and into the iliofemoral system.' Thrombosis of the popliteal or more proximal veins is more likely to result in pulmonary embolism than is isolated deep calf vein thrombosis. In most instances the thrombotic process extends directly from the calf upward into the proximal system. On rare occasions the process is isolated in the iliofemoral system, but even in these instances it is usually associated with concurrent separate deep calf vein thrombosis. The pattern of isolated iliofemoral thrombosis is seen most often in individuals who have undergone hip replacement. Venous thrombosis of the lower extremity nearly always precedes pulmonary embolism. There are some reports of clinically significant pulmonary embolism occurring in individuals with thrombosis of the superior vena cava, the innominate and axillary veins. However, these instances are rare and are usually associated either with direct trauma or a hypercoagulable state. Similarly, there are anecdotal reports of pelvic vein thrombosis causing pulmonary embolism, but these instances are also rare and worthy of note in the literature. Pelvic vein thrombosis does occur in individuals following pelvic trauma or malignancy and during pregnancy. However, it is very rare for these thrombi to result in clinically significant pulmonary embolism without the concurrent presence ofdeep venous thrombosis ofthe lower extremity. Consequently, the approach to the diagnosis of pulmonary embolism must also include a search for deep venous thrombosis of the lower extremity. This search has been greatly simplified by the emergence ofBmode ultrasonographywith compression (CUS).2 3 The usefulness of this non-invasive test not only establishes the diagnosis but, when it repeatedly remains negative it identifies a low risk group for subsequent pulmonary embolism of proximal deep vein thrombosis. Consequently, the test can be used to stratify the risk of individuals with suspected pulmonary embolism having subsequent morbid events over the next three months.