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). 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. 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. 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.