The Use and Reproducibility of Transabdominal Ultrasound to Provide Indices of Left Common Iliac Vein Diameter

Abstract

Introduction: May Thurner Syndrome (MTS) is a rare vascular condition whereby the left common iliac vein (CIV) is compressed by the overlying right common iliac artery. It can lead to serious medical problems such as deep vein thrombosis or pulmonary embolism. Currently the gold standard for diagnosis is invasive imaging techniques such as catheter venography or intravascular ultrasound. Opinions differ on the best way to use transabdominal ultrasound to determine CIV compression and the size at which a CIV measured with transabdominal ultrasound would indicate compression and necessitate the need for further imaging. Aims: This thesis aims to investigate the use and reproducibility of transabdominal ultrasound to provide indices of left CIV diameter, to aid diagnosis of MTS in patients presenting with unexplained left leg swelling. Methods: 40 patients were recruited from the vascular department at Imperial College Healthcare NHS Trust. 20 patients were symptomatic for left leg venous disease and 20 patients were asymptomatic. Three clinical vascular scientists performed a transabdominal ultrasound assessment on each patient, measuring the diameter of the left CIV three times with the patient supine and three times with the patient tilted to 45-degrees reverse trendelenburg (RT), to assess for intra- and inter-operator reliability. Results: Readings were obtained from 36 out of 40 patients, partial data obtained from 3 patients and no readings could be obtained from 1 patient. Analysis of the data from the 36 patients found an average diameter of the left CIV of 8.0mm ± 3.8mm in the symptomatic group (n=16, 6 male, 10 female) and 7.8mm ± 2.7mm in the asymptomatic group (n=20, 11 male, 9 female). There was no statistically significant difference in left CIV diameter between the symptomatic group and asymptomatic group, however, there was a statistically significant difference in left CIV diameter based on posture (p<0.05). The diameter of the left CIV measured 7.0mm ± 2.6mm when assessed supine and 9.0mm ± 3.3mm when tilted to 45-degree RT. Intra-operator reliability was excellent (ICC=0.92 with 95% confidence interval =0.90-0.93) whereas inter-operator reliability was moderate (ICC=0.67 with 95% confidence interval 0.60-0.72). Conclusion: This study determined an average left CIV diameter of 7.0mm ± 2.6mm as measured by transabdominal ultrasound. Importantly, the diameter of the left CIV significantly increases when a patient is examined in the 45-degree RT position (7.0mm ± 2.6mm vs 9.0mm ± 3.3mm, supine vs tilted; p<0.05). This suggests that symptomatic patients presenting with a left CIV measuring smaller than 7.0mm ± 2.6mm should be reassessed in the tilted position, and if still measuring smaller than this, further investigations should be considered. In this study intra-operator reliability was excellent whereas inter-operator reliability was moderate, therefore results from scans should be interpreted with caution. Further larger scale studies using MTS patients would be beneficial to confirm the average diameter measurements established in this study and to further determine a diameter range that would be highly suggestive of left CIV compression when examined using transabdominal ultrasound