Effect of anatomic distribution of pulmonary emboli on interobserver agreement in the interpretation of pulmonary angiography

OBJECTIVE: This study examines the anatomic distribution of emboli on pulmonary angiography and attempts to determine the relationship of vessel size to interobserver agreement, two factors having important implications in comparing pulmonary angiography with cross-sectional imaging for pulmonary embolism. MATERIALS AND METHODS: One hundred twenty-five consecutive pulmonary angiograms were reviewed retrospectively by three interventional radiologists. Initial interpretations were recorded and compared to determine interobserver agreement on a per-patient and per-embolus basis. Discordant interpretations were reviewed by all radiologists for a consensus interpretation. RESULTS: Unanimous per-patient agreement occurred in 91% (114/125) of initial interpretations. The largest artery containing acute pulmonary embolism was segmental or larger in 24 patients (83% of patients with acute positive findings, 19% of all patients) and subsegmental in only five patients (17% and 4%, respectively). On a per-patient basis, initial interobserver agreement averaged 45% and unanimous consensus agreement was achieved for 79% of patients having isolated subsegmental pulmonary embolism. Consensus readings altered initial per-patient interpretations for 30% of patients having only subsegmental pulmonary embolism; per-embolus interpretations were altered for 37% of all subsegmental emboli. CONCLUSION: Subsegmental emboli occurring as isolated findings are relatively rare. Approximately one third of subsegmental emboli and one third of patients having isolated subsegmental emboli may be initially misdiagnosed on pulmonary angiography. Objections to cross-sectional imaging for pulmonary embolism based on the inability to detect subsegmental pulmonary embolism when compared with pulmonary angiography should be reexamined with this data in mind.