Small perfusion defects in suspected pulmonary embolism

Abstract

The purpose of this investigation was to assess the diagnostic value of 1 to 3 versus > 3 small subsegmental defects on perfusion lung scans of patients with suspected acute pulmonary embolism (PE).

Methods: Data from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) were evaluated from patients with suspected acute PE. Angiograms, follow-up data and outcome classifications were used to determine PE status. The perfusion scan of included patients showed only small subsegmental defects ( < 25% of a segment) in the presence of a regionally normal chest radiograph. Findings on the ventilation scan were irrelevant.

Results: The positive predictive value for PE of perfusion lung scans with 1-3 small subsegmental defects was 1% to 3%, depending on the group analyzed. The positive predictive value for the PE of perfusion lung scans with > 3 small subsegmental defects was 11% to 17% depending on the group analyzed.

Conclusion: Perfusion lung scans with 1-3 small subsegmental defects satisfy the criterion for a very low probability ( < 10% positive predictive value) for PE and perfusion lung scans with > 3 small subsegmental defects satisfy the criteria for a low probability ( < 20% positive predictive value) for PE.