Abstract No. 50 May-Thurner syndrome: can it be diagnosed on a solitary MRV study?

Abstract

The aim of this study is to evaluate the significance of identifying left common iliac vein (CIV) compression by the right common iliac artery on MRV. This IRB approved, HIPAA compliant study involved a search of our radiology department's electronic database for the term ‘May-Thurner’ over a 5-year period from 2006-2011. 214 patients were diagnosed with May-Thurner syndrome based on findings on MRV. From these patients we identified those who underwent MRI or CT within a time period of 6 months before or any time after the MRV and did not have any interventional procedure performed between the two studies. 36 patients met these criteria. The anteroposterior diameter of the left CIV was measured where it was crossed by the right common iliac artery as well as a caudal segment in the iliac vein. The degree of venous compression was calculated as the diameter of the left CIV at the site of crossing of the right common iliac artery divided by the diameter of the uncompressed caudal left CIV. We performed Wilcoxon rank-sum tests to determine whether the difference in degree of venous compression in the two studies was significant. The majority (89%) of the comparison studies were CT and were performed on average 4 months post MRV. On the MRV, in which a diagnosis was rendered, all patients had on average 62% compression of the CIV (range 40-83%). However, on the comparison study, there was an average compression of 39% (range 3-78%). The mean change in degree of compression between the two studies was 25% (p<0.0001), with a range from 3% increase to 70% decrease in degree of compression in the comparison study. Our data indicate a false positive rate of 47%. In select cases, we further show significant compression in the supine position, but when prone, imaging demonstrated normal iliac vein diameter. The sole finding of a compressed left common iliac vein on a solitary MRV study is not sufficient to make the diagnosis of May-Thurner syndrome. Iliac vein compression is a chronic condition leading to permanent venous wall remodeling and spur formation implying that the venous diameter should not change as a function of volume status or positioning.