CT pulmonary angiography and the over diagnosis of pulmonary embolism

A recent article in the Texas Heart Institute Journal by Dr. Herb Fred includes this statement:

In the teaching hospital where I work, “fishing” is rampant. By fishing, I mean scanning the body part thought to be the source of the patient's complaint or problem, hoping thereby to reel in some sort of diagnosis.48 In these cases, the physician essentially bypasses the history and physical examination and, guided solely by the patient's chief complaint, proceeds directly to CT scanning with no particular pre-test diagnosis foremost in mind. This sport typically takes place in the emergency department, where almost all patients entering with chest pain (not further described) or shortness of breath (not further defined) promptly undergo contrast-enhanced chest CT. It should be obvious, however, that such robotic, indiscriminate, and unduly expensive screening is bound to uncover pulmonary arterial filling defects every now and then. And it does. The defects occasionally appear in the main or lobar arteries, but most of the time they appear in just 1 or 2 segmental or subsegmental branches—areas where reconstruction artifacts or contrast-streaming can produce a false-positive interpretation. Nevertheless, once these defects are detected, all thinking stops, pulmonary embolism becomes the primary diagnosis, and anticoagulation automatically ensues.

But should it, necessarily? That question, as addressed in this paper, gets a little complicated and it deals with two different situations: 1) pulmonary artery filling defects discovered incidentally when chest CT scanning was done for non cardiovascular indications and 2) filling defects (“positive” study) seen when scanning is done in knee jerk fashion to patients with chest pain without prior careful examination or thought.

It is unclear in many such cases whether anticoagulation is necessary, particularly if the filling defects are subsegmental and isolated.

So one may end up dealing with a situation in which thinking which should have taken place before imaging is considered has to be done after the patient “rules in” for PE. That inevitably leads to more testing, for confirmation and to assess risk coupled with clinical judgment applied better late than never.