Small pulmonary artery defects are not reliable indicators of pulmonary embolism

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.

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.

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%).

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.