Maximal Venous Outflow Velocity: A Novel Technique for Detecting Ileocaval Occlusive Disease

Background: Compression of the left iliac vein by the overlying right iliac artery (May-Thurner's Syndrome, MTS) can cause left leg swelling due from outflow obstruction, increasing risk for deep vein thrombosis. Discerning pathological anatomy from normal ileocaval anatomy can be challenging, as planar imaging provides anatomic, rather than functional information. Traditional DUPLEX interrogation of the leg provides data limited to only the infrainguinal venous system. Our hypothesis is that DUPLEX-derived maximal venous outflow velocity (MVOV) can be a useful screening tool as an adjunct to lower extremity DUPLEX to screen for patients with ileocaval obstruction.
Methods: MVOV studies of 14 patients with unilateral leg swelling from 2000 - 2009 were compared to a control group of 30 asymptomatic volunteers. Right and left legs of the test group and symptomatic and asymptomatic legs were compared to each other and to controls using t-test. A ratio of symptomatic to asymptomatic extremities was compared to left over right in the controls to generate an index compatible with pathological venous impedance. The same parameters were also compared after endovenous stenting for positive venographic findings in patients with MTS.
Results: Symptomatic extremities had reduced absolute MVOV's (p= 0.021) compared to the contralateral extremity. In patients undergoing endovascular stenting for MTS (4), there was observed a significant increase in MVOV of the treated leg (p=0.012) and the post-treatment MVOV measurements in the left and right legs were not significantly different (p=.213). On review, we found that a left to right MVOV index of <1.06 correlated with positive angiographic findings and success of treatment (p=0.0434). In this same group, computerized tomography with venous contrast predicted a positive venographic finding in 60% of the patients (3/5).
Conclusions: As most patients with unilateral leg swelling undergo routine Duplex ultrasound to evaluate for DVT, MVOV studies can be obtained without added risk, exposure, and little technical cost. MVOV and a calculated index of <1.06 seems to be predictive of success of intervention, even when CT interpretation suggested otherwise.