Clinical impact of findings supporting an alternative diagnosis on CT pulmonary angiography in patients with suspected pulmonary embolism.

Background: CT pulmonary angiography (CTPA) is commonly used as the first imaging test in the diagnostic workup of patients with suspected pulmonary embolism (PE). Other CTPA findings may provide an alternative explanation for signs and symptoms in these patients, but the clinical impact is not clear.
Methods: In 203 consecutive patients with suspected PE, we prospectively evaluated the clinical implication of abnormalities on CTPA. Alternative diagnoses were defined on clinical grounds before and after CTPA. Subsequent diagnostic tests and therapeutic consequences were assessed by criteria defined a priori.
Results: Sixty-one of the 203 patients (30%) had no abnormality on CTPA. Thirty-nine patients (19%) were given a diagnosis of PE. Before CTPA, alternative diagnoses were suspected in 97 patients (48%). Findings supporting an alternative diagnosis were detected in 88 patients (43%). In 28 patients, this was a new finding; in 18, a conclusive and previously unknown alternative diagnosis was made on the basis of the CTPA results. Overall, the findings supporting alternative diagnoses had therapeutic consequences in 10 patients (4.9%). Incidental findings (nodules and enlarged lymph nodes) requiring diagnostic procedures were present in 17 patients (8.4%), with one (0.5%) having a therapeutic consequence.
Conclusions: In patients undergoing CTPA for suspected PE, findings supporting an alternative diagnosis were found in almost one-half of the patients. However, in only a few patients, the alternative diagnosis had therapeutic consequences. Hence, CTPA should principally be used to confirm or exclude PE in high-probability cases but not to establish an alternative diagnosis.