Reply

In response to the Letter to the Editor on our recent article “Prevalence and predictors of radiological left common iliac vein compression in asymptomatic patients,”¹ we agree with Gong et al that computed tomography (CT) venography is useful in measuring left common iliac vein (LCIV) compression, although it may not be the most cost-effective diagnostic modality.

Another commonly used noninvasive method to detect LCIV compression is duplex ultrasound, which is highly sensitive, at a lower cost, and without any risk of iodine contrast. In expert hands, ultrasound should be the first-line imaging modality, as it can provide an estimate of venous stenosis and hypertension by measure of the flow upstream and downstream to the stenosis.² Intravenous ultrasound venography is more accurate to define the anatomy of the stenosis, but it may require intravenous contrast, which is quite expensive. Recently, magnetic resonance venography has emerged as a valid diagnostic tool.³ Therefore, if used for screening purposes alone, intravenous ultrasound venography and magnetic resonance venography are not appropriate.

In our study, we used contrast-enhanced CT to evaluate the iliac vein compression. All the patients had a CT scan because of an annual heath check or abdominal pathologies, including appendicitis, inguinal hernia, intestinal obstruction, and cholangitis. Those CT images were already available; therefore, our patients were not exposed to extra radiation. The anteroposterior diameter of the LCIV was measured on four horizontal planes of CT in venous phase; the ‘normal’ diameter of the LCIV was calculated using the mean value of three sites: proximal and distal segment to the most severe compression by right iliac artery, and the segment of the LCIV without compression. The mean diameter of the uncompressed LCIV was 12.2 ± 2.3 mm in the 1698 patients included in our study. This also provided an anatomic reference for LCIV diameter if we perform angioplasty and stenting for May-Thurner Syndrome. The iliac vein appeared as an oval shape on the transverse plane of the CT scan in the supine position. Ideally, the diameter of the iliac vein should be measured on the reconstructed image perpendicular to the venous central line, which allows more accurate calculation, but this required additional sophisticated software, and the contrast phase needed to be very precise. Nonetheless, we agree with Gong et al that further studies comparing different measurement modalities will improve our understanding of LCIV compression.

Disclosures

None.