May-Thurner syndrome: can it be diagnosed by a single MR venography study?

PURPOSE We aimed to evaluate the longitudinal stability of left common iliac vein (LCIV) compression by the right common iliac artery on magnetic resonance venography (MRV). MATERIALS AND METHODS This retrospective study included 214 patients diagnosed with May-Thurner syndrome by MRV. We identified a subset of patients who underwent contrast-enhanced cross-sectional imaging of the pelvis six months before or anytime after the MRV and did not undergo any interventional venous procedures between the two studies; 36 patients met these criteria. The degree of venous compression was calculated in both the index and comparison study. RESULTS On the index MRV, the mean compression of the LCIV was 62%. However, on the comparison study in the same patients, the mean compression was 39%. The mean change in degree of compression between the two studies was 23% (P < 0.0001), ranging from a 12% increase to 69% decrease in degree of compression on the comparison study. CONCLUSION The compressed LCIV on a single MRV study was not stable over time and thus may be insufficient to diagnose May-Thurner syndrome.