Abstract No. 507 Quantifying the accuracy of magnetic resonance venography assessments in the diagnosis of May-Thurner syndrome

Abstract

May-Thurner syndrome (MTS) is a venous anatomical abnormality where the right iliac artery compresses the left iliac vein. Magnetic resonance venography (MRV) is often used to diagnose stenosis associated with MTS. While previous studies have hypothesized that MRV may inaccurately estimate the extent of compression in MTS, there is need to clarify the role of MRV in the diagnosis of this disease.1,2 The purpose of this study is to evaluate interobserver variability in diagnosis and classification of MTS by MRV. An IRB-approved retrospective analysis of 33 MRVs performed at The George Washington University Hospital between January 2012 and December 2015 for “left leg swelling” was performed. These studies were evaluated by three board certified interventional radiologists for iliac vein compression on a simple grading scale (“none,” “mild” i.e., 25% stenosis, “moderate” i.e., 50% stenosis, or “severe” i.e., 75% stenosis) in a blinded fashion. Physician ratings were compared to assess provider variation in MRV evaluation. An analysis was then performed to determine the interrater reliability for assessing the degree of compression. 33 MRVs were reviewed in total. On average, the providers agreed 85.86% of the time on the presence of any stenosis. However, the interrater consensus dropped to 44.44% when reporting the degree of stenosis. Fleiss’ Kappa scores were calculated to quantify the interrater reliability on assessing the degree of stenosis. Interestingly, the grading of compression severity had a low interrater reliability (Fleiss’ k = 0.24) demonstrating only fair agreement between providers. While MRV appears reliable in assessing the presence of any stenosis, Fleiss’ Kappa analysis indicates substantial variability in clinical judgement of the degree of stenosis of the left common iliac vein when diagnosing or ruling out MTS. Low interrater reliability of reading MRVs therefore suggests that more definitive diagnostic methods such as catheter venography supplemented with Intravascular Ultrasound (IVUS) may be more accurate to diagnose MTS.