Small Pulmonary Artery Defects Are Not Reliable Indicators of Pulmonary Embolism

Abstract

OBJECTIVES: To evaluate the rate of agreement of pulmonary embolism diagnosis in computed tomography (CT) pulmonary angiogram studies and to evaluate the rate of inaccurate interpretations in the community hospital setting. METHODS: Using the keywords "pulmonary embolism/embolus/emboli," the radiology information system was searched for CT pulmonary angiograms performed over a 3-year period at three U.S. community hospitals. Studies containing probable or definite pulmonary emboli were independently reviewed by four subspecialty thoracic radiologists. MEASUREMENTS AND MAIN RESULTS: Agreement about the presence of pulmonary embolism progressively decreased with decreasing diameter of pulmonary vascular lesions (P < 0.0001). There was a sharp fall in observer agreement for pulmonary embolism of subsegmental lesions (P < 0.0001). The frequency of agreement decreased with decreasing quality of the imaging examination (P < 0.0001). Community radiologists were prone to false-positive pulmonary embolism diagnosis of subsegmental and/or small pulmonary arterial defects. The probability of a false-positive diagnosis and indeterminate examinations progressively increased with: (1) more peripheral location of the lesion, (2) decreased size (short-axis diameter) of the lesion, and (3) diminishing quality of the CT examination. Forty-eight of 177 (27%) of subsegmental vascular defects identified by community radiologists were deemed indeterminate, and 27 of 177 (15%) of subsegmental vascular defects were judged to be false positive for pulmonary embolism by the consensus diagnosis. Fifty-four of 274 (20%) vascular defects with short axis less than 6 mm were indeterminate for pulmonary embolism, and 37 of 274 (14%) of vascular defects with short axis less than 6 mm were false positive for pulmonary embolism. Eleven of 13 (85%) of vascular lesions identified as pulmonary emboli on the lowest-quality CT examinations were false positive or indeterminate for pulmonary embolism. False-positive examinations were most often due to respiratory motion artifact (19/38, 50%). CONCLUSIONS: There is relatively poor interobserver agreement for subsegmental and/or small pulmonary artery defects, especially in CT pulmonary angiograms degraded by technical artifacts. These factors can lead to an increased frequency of inaccurate interpretation or indeterminate diagnosis of subsegmental and/or small defects. Caution is indicated in interpreting the significance of small vascular defects in CT pulmonary angiograms.