Iliac vein compression in an asymptomatic patient population

May-Thurner syndrome is a well-recognized anatomic variant that is associated with the development of symptomatic acute venous thrombosis of the left iliac vein. However, the natural frequency of compression of the left iliac vein and its clinical significance in asymptomatic disease has not been established. Therefore the purpose of this descriptive anatomic study was to determine the incidence of left common iliac vein compression in an asymptomatic population. A retrospective analysis of medical records and helical abdominal computed tomography scans was conducted in 50 consecutive patients evaluated in the emergency department because of abdominal pain. Medical records were reviewed for symptoms and risk factors for deep venous thrombosis, and data were collected and reported according to the Joint Society Reporting Standards for acute lower extremity venous thrombosis. All computed tomography was performed with intravenous contrast medium, and 2-mm to 5-mm axial images were obtained. The minor diameter of the common iliac arteries and veins was measured. The technique of transverse image measurement was validated with multiplanar reconstructions and orthogonal diameter measurements in a subset of subjects. Statistical analysis was performed with the Student t test or Spearman rank correlation. Mean age of subjects without symptoms was 40 years (range, 19-85 years), and 60% (n = 30) were female patients. The mean acute lower extremity venous thrombosis risk factor score was 1.16 ± 0.23 (range, 0-6; maximum possible score, 28). It was surprising that 24% (n = 12) of patients had greater than 50% compression and 66% (n = 33) had greater than 25% compression. Mean compression of the left common iliac vein was 35.5% (range, −5.6%-74.8%). The structure most often compressing the left common iliac vein against the vertebral body was the right common iliac artery (84%). There was no strong correlation between patient age or common iliac artery size and compression of the left common iliac vein. However, women had greater mean compression of the left common iliac vein (women, 41.2% ± 3.1%; men, 27.0% ± 3.0%; P = .003). Hemodynamically significant left common iliac vein compression is a frequent anatomic variant in asymptomatic individuals. Therefore compression of the left iliac vein may represent a normal anatomic pattern that has thus far been thought of as a pathologic condition.