The limitations of carotid sonography: Interpretive and technology-relatederrors

OBJECTIVE. This study compared carotid artery sonography with angiography t o determine, in retrospect, which types of sonographic errors arose from in correct interpretation of sonographic images and which errors could be ascr ibed to the limitations of sonographic imaging. MATERIALS AND METHODS, A review of all patients who underwent carotid arter y sonography and angiography between 1993 and 1997 at our institution revea led 66 patients with complete sets of studies, yielding 132 examinations (r ight or left). Studies were not reinterpreted and angiography was considere d to be the gold standard. Only stenoses of 60% or greater were included in our study. If the degree or location of stenosis differed on the two imagi ng studies, they were reviewed together to classify the type of sonographic error. RESULTS. We found complete agreement of sonography and angiography in 115 c ases (87%) and discrepancies in 17 (13%). Thirteen of 17 sonographic errors were false-positive interpretations and three were false-negative interpre tations. One was an error in location. Retrospective review showed seven in terpretive errors. In all these cases, the color Doppler image better revea led the degree of stenosis, Other complicating factors included inconsisten cies between absolute velocities, velocity ratios, and waveforms obtained w hile a patient was being treated with an intraaortic balloon pump, In the o ther 10 discrepancies, the sonographic interpretation was accurate, Seven o f these cases were false-positive interpretations in patients with contrala teral occlusions or stenoses. The other three cases in this group showed lo ng segments of stenosis, ulcerations, or tortuous vessels on angiography. CONCLUSION. Our study suggests that increased accuracy can be achieved in t he interpretation of carotid artery sonography by meticulous attention to t he color image. When color Doppler sonography is technically limited by tor tuosity or ulceration, or if significant contralateral disease is present, misinterpretation is more likely.