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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 4  |  Issue : 4  |  Page : 116-122

The left common iliac vein area: Analysis of chronic venous disease patients with and without MTS


Department of Vascular Surgery, School of Medicine, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University, Shanghai, China

Date of Submission16-May-2021
Date of Decision20-Jul-2021
Date of Acceptance26-Jul-2021
Date of Web Publication21-Dec-2021

Correspondence Address:
Dr. Yin Min-Yi
Department of Vascular Surgery, School of Medicine, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University, Shanghai 200011
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2589-9686.333001

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  Abstract 


OBJECTIVE: To analyze the normal reference left common iliac vein (LCIV) area in chronic venous disease (CVD) patients with or without May–Thurner syndrome (MTS) and its relevant influencing factors.
MATERIALS AND METHODS: A prospective analysis of patients with left lower extremity CVD was conducted in a single institution from January to August 2019. A total of 326 patients, 98 with MTS and 228 without MTS after computed tomography (CT) venography, were finally enrolled in this study, and their basic information was recorded. MTS cases were distinguished from non-MTS cases by calculating area stenosis rate with CT three-dimensional reconstruction. The reference area of LCIV was also defined and calculated to analyze its coefficient of variation and relationship with influencing factors in patients with and without MTS.
RESULTS: Ninety-eight cases of MTS and 228 cases of non-MTS were finally analyzed. In the MTS group, the mean area of reference LCIV was significantly lower (116.29 ± 53.17 mm2 vs. 160.44 ± 52.99 mm2, P < 0.01) and showed greater variability (0.21 ± 0.13 vs. 0.16 ± 0.08, P = 0.04) compared with non-MTS group. Obesity radio was significantly higher in non-MTS group (28.5% vs. 16.3%, P = 0.03). In both MTS and non-MTS groups, the increase of body mass index (BMI) was generally associated with statistically significant increases in the LCIV area (P = 0.002 and P = 0.005), while other factors showed no statistically significant correlation.
CONCLUSIONS: The reference area of LCIV was redefined in this study. We found that the increase of the LCIV area in both MTS and non-MTS groups was correlated with an increase in BMI. Furthermore, a smaller area of reference LCIV and more variability in the LCIV area were found in the MTS group in contrast to the non-MTS group.

Keywords: Chronic venous disease, computer tomography venography, left common iliac vein, May–Thurner syndrome


How to cite this article:
Cheng-Hao Y, Xin-Wu L, Xin-Tian H, Xiao-Bing L, Kai-Chuang Y, Zhen Z, Xu-Hui W, Peng-Hui W, Min-Yi Y. The left common iliac vein area: Analysis of chronic venous disease patients with and without MTS. Vasc Invest Ther 2021;4:116-22

How to cite this URL:
Cheng-Hao Y, Xin-Wu L, Xin-Tian H, Xiao-Bing L, Kai-Chuang Y, Zhen Z, Xu-Hui W, Peng-Hui W, Min-Yi Y. The left common iliac vein area: Analysis of chronic venous disease patients with and without MTS. Vasc Invest Ther [serial online] 2021 [cited 2022 Aug 19];4:116-22. Available from: https://www.vitonline.org/text.asp?2021/4/4/116/333001




  Introduction Top


May–Thurner syndrome (MTS), also known as iliac vein compression syndrome or Cockett's syndrome, is a lower extremity venous obstruction disease that is typically caused by the right common iliac artery (RCIA) compressing an overlying left common iliac vein (LCIV).[1] MTS is considered an important pathogenic factor for chronic venous disease (CVD).[2] Furthermore, MTS tends to occur in 18%–49% of the cases of lower extremity deep venous thrombosis (DVT) and is 3–8 times more common on the left side.[3],[4]

Although the measurement of area stenosis represented by intravenous ultrasound (IVUS) has gradually replaced the traditional diameter stenosis measurement as the gold standard for the diagnosis of MTS,[5],[6],[7] there are still some shortcomings, especially the lack of the unified standard of reference vein area.[8] Raju et al. have estimated fixed reference vein area using indirect methods, including Poiseuille's law and Young's scaling law. They analyzed the top 5% of measurements in a cohort of patients to provide estimates of normal LCIV area and diameter.[9],[10] Although this fixed value method is relatively simple, the accuracy of its estimates is difficult to determine due to the differences in race, gender, height, and weight. Other scholars suggest using the relatively normal LCIV, which is far from compression lesion, as a reference vein area.[11] Yet, because of the high variability of capacitance veins and the venous tortuosity in some cases, it is often difficult to directly determine the relatively normal LCIV.[12] Learning how different factors such as gender, age, height, and weight affect LCIV area could further optimize the determination of area stenosis and the appropriate size of the stent.

The purpose of this study was to analyze the normal reference LCIV area in CVD patients with or without MTS. Relevant influencing factors, such as gender, age, body mass index (BMI), and symptoms, were analyzed in both groups.


  Materials and Methods Top


Study group

All patients with left lower extremity CVD underwent ultrasonography to exclude the thrombotic diseases in our department between January and August 2019. Those diagnosed with moderate-to-severe symptomatic (clinical C3 or higher level) nonthrombotic CVD were included in the current study. Exclusion criteria included previous CVD surgical or interventional treatment, vascular malformation, acute deep vein thrombosis, postthrombotic syndrome, lymphedema, pelvic malignancy, retroperitoneal fibrosis, heart failure, renal failure, and iodine allergy. Computed tomography venography (CTV) was performed in all enrolled patients to determine the patency of iliac vein and inferior vena cava. The basic information, including gender, age, weight, height, and symptoms, were recorded.

The study was approved by the Shanghai Ninth People's Hospital Institutional Review Board. All patients signed informed consent before CTV.

Computed tomography venography

A total of 351 CTV examinations were performed on a 64-detector CT scanner (GE Healthcare, WI, Boston, MA) with 120 mL of nonionic iodine contrast (350 mg/mL, Yangtze River Pharmaceutical Group, TaiZhou, China) at a rate of 4 mL/sec using a power injector through 18-to 20-gauge indwelling needle in the antecubital vein. CTV was started 120–180 s after contrast medium injection from foot to diaphragm with the following parameters: 120–140 kV of tube voltage, 300 mA of tube current, 1.5 mm pitch, 0.6 mm collimating, and 1.5 mm reconstruction thickness.

Three-dimensional reconstruction of computed tomography venography

The Dicom data were uploaded to the Medraw three-dimensional (3D) reconstruction workstation (Image Medraw Technology, Shanghai, China). Image threshold segmentation was set as 150–200 Hu to reconstruct the iliac/IVC and iliac/abdominal aorta, respectively, with 3D reconstruction algorithm [Figure 1]a. Cross-sectional center points were established from the iliac vein to IVC and connected to form the central line. The potential LCIV compression point, defined as the intersection of the central line and the RCIA, was analyzed with the cross-section perpendicular to the central line [Figure 1]b. The area of the potential LCIV compression was calculated [Figure 1]c, and the average area of 5 segments of the LCIV far from the potential compression point was taken as the reference area. Area stenosis rate of potential venous compression point = 1 - (area of compressed cross section / area of fitting circle). Area stenosis rate greater than 50% was defined as significant venous compression. The reference area of LCIV and its coefficient of variation in patients with and without MTS were analyzed in the current study. Two senior vascular surgeons who were blinded to the patient's symptoms independently reviewed the CTV results.
Figure 1: Computed tomography venography three-dimensional reconstruction and measurement of venous area stenosis rate. (a) Computed tomography venography three-dimensional reconstructions of iliac/inferior vena cava and iliac/abdominal aorta. The suspected venous compression point is marked with “A” and “B”. (b) Suspected compression veins were analyzed with the cross-section perpendicular to the central line (A1). (c) Circumference of the suspected compression vein is outlined (red line) and calculated

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Statistical analysis

Individual data were summarized using frequencies or percentages for categorical variables and mean ± standard deviation for continuous variables. Statistics were computed with SPSS version 13.0 (SPSS, Inc., Chicago, Illinois, USA). ANOVA test and independent-sample t-test were used to compare the reference LCIV area and its coefficient of variation in patients with and without MTS. Linear regression with subject parameters (gender, age, BMI, and symptoms) was done for the reference LCIV area. P < 0.05 was considered statistically significant.


  Results Top


Out of 351 patients with CTV, 119 patients were diagnosed with at least one significant venous compression, including 15 cases of inferior vena cava compression and 6 cases of dual LCIV compression, all of which were excluded. Four of the remaining 232 non-MTS patients were also excluded due to chronic iliac venous thrombosis. Finally, 98 cases of MTS and 228 cases of non-MTS were enrolled in the current study. The basic information, comorbidities, and clinical symptoms of the two groups are listed in [Table 1]. There was no difference between the two groups in any of the indexes except for the obesity ratio, which was significantly higher in the non-MTS group compared to the MTS group (28.5% vs. 16.3%, P = 0.03).
Table 1: Patient demographics (n=92)

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The mean area of reference LCIV was significantly lower in the MTS group compared with the non-MTS group (116.29 ± 53.17 mm2 vs. 160.44 ± 52.99 mm2, P < 0.01). With regard to the area variation, the reference LCIV in the MTS group showed greater variability compared with the non-MTS group (0.21 ± 0.13 vs. 0.16 ± 0.08, P = 0.04) [Table 2].
Table 2: Comparison of mean area and variability of area of the common iliac vein between non-May-Thurner syndrome and May-Thurner syndrome group

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In both MTS and non-MTS groups, the increase of BMI was generally associated with statistically significant increases in LCIV area (P = 0.002 and P = 0.005). However, gender, age, and symptoms showed no significant effect on LCIV area in two groups [Table 3] and [Table 4]. The results of simple linear regression analysis predicted the LCIV area with BMI in both MTS group (P = 0.003; R2 = 0.17; Y = 69.00 + 18.54X) and non-MTS group (P = 0.001; R2 = 0.27; Y = 102.69 + 21.94X).
Table 3: Comparison of the mean area of common iliac vein in May-Thurner syndrome patients with different gender, age, body mass index, and symptoms

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Table 4: Comparison of the mean area of common iliac vein in non-May-Thurner syndrome patients with different gender, age, body mass index, and symptoms

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  Discussion Top


Selecting the normal reference vein area has gained increasing interest from researchers following the development of the method based on the area stenosis rate in MTS diagnosis. The fixed reference area and adjacent normal vein area are the most commonly used reference area methods; however, their accuracy is still not fully determined.[12],[13] In the current study, CTV 3D reconstruction was used for imaging evaluation of the LCIV reference area in a patient with and without MTS. The results showed that the LCIV reference area in both groups was smaller than the previously estimated fixed reference area. Furthermore, the mean area of the reference LCIV in the MTS group was significantly smaller than that in the non-MTS group. In contrast, the variability of the area was significantly higher compared to the latter group. The increase of the LCIV area in both groups was correlated with the statistically significant increase in BMI, but not with gender, age, and symptoms.

The fixed reference area method was initially proposed by Raju et al., who used indirect methods, including Poiseuille's equation and Young's scaling ratio, to estimate normal vein diameters.[9],[10] According to the above calculation, CIV's normal area and diameter were determined to be 200 mm2 and 16 mm. More recent data from actual patient measurement suggested a smaller normal CIV area or diameter than Raju's results. Arendt et al. analyzed the average maximum diameters of CIV in patients with underlying venous disease and found that the left and right sides' diameter was 12.2 mm and 13.6 mm, respectively.[11] Aurshina et al. also reported smaller reference CIV area results with IVUS in both MTS and non-MTS patients.[13] The normal area of proximal, middle, and distal CIV of the two groups were 146 mm2, 149 mm2, and 162 mm2 and 170 mm2, 176 mm2, and 190 mm2, respectively. In the current CTV evaluation study, the phenomenon of lower reference LCIV area was also detected. The reference area of LCIV in MTS and the non-MTS group was comparable to previous studies at 116.29 mm2 and 160.44 mm2, converted to 12.2 mm and 14.3 mm in diameter, respectively. Although the fixed reference area method has some advantages due to the difficulty of directly measuring normal veins, it seems that indirect calculation overestimates the normal area of CIV. The analysis of only the top 5% values may actually come from dilated veins due to more serious stenosis, resulting in an overestimation of the actual area in Raju's study.

The ignorance of variability in the vein area is another disadvantage of the fixed reference area method. Previous studies have shown that the deep vein's diameter and area in the lower extremity were significantly affected by gender, age, weight, height, race, and BMI.[11],[14],[15],[16],[17],[18] Fronek et al. assessed the normal CFV dimensions in a cohort assembled to permit contrasts using sex, age, and ethnicity and found that there was an overall decline in CFV diameter with increasing age.[15] Smaller CFV diameter was also found in female, Asian and Hispanic groups. Maximum diameters of deep vein from the diaphragm to the knee were measured from CTV studies by Arendt et al.[11] Increases in weight and height were generally associated with statistically significant but modest increases in vein diameter from CTV results. However, unlike previous studies, females were detected to have significantly larger vessels from external iliac veins to suprarenal IVC compared to males. Although there is no consistent result on the influencing factors of vein dimensions in previous studies, excessive body weight and BMI have been frequently considered the main factors causing the increase of vein size,[17] which is consistent with our results. Multiple factors, including gender, age, BMI, and symptoms, were analyzed in the current study. The increase of BMI was the only factor related to the increase of LCIV area in both MTS and non-MTS groups. The reason for these varieties may be secondary to the increased venous reflux and venous pressure, which are caused by the raised intraabdominal pressure. Nonetheless, further research is needed to investigate these hypotheses.

Nicolaides et al. have brought a more convincing explanation to this conclusion. They introduced the concept of lower limb outflow resistance (LOR).[19] Another potential factor that influences LOR in patients with MTS is the collateral circulation development as well as the stenosis rate of venous area. People with higher BMI often require larger blood flow in the lower extremities because of their higher basal metabolic rate, which causes a burden on the venous collateral circulation of the lower extremities, resulting in a compensatory increase in the area of LCIV. more Another explanation is the volume of blood flow and blood velocity of people with higher BMI tend to be higher than these with low BMI. The stimulation of increased blood flow velocity will lead to the remodeling of the vein wall to a larger diameter.

There is a lack of comparative studies on the variety of reference LCIV area between MTS and non-MTS groups. Aurshina et al. utilized the IVUS technology to measure the normal areas of non-diseased CIV in patients who were stented and those who were not stented.[20] The results showed a significant difference, with larger areas in non-stented patients in the distal common iliac vein (P = 0.04) and inferior vena cava (P = 0.01). Yet, the authors did not further analyze the causes of difference. The same phenomenon was observed in the present study. The reference LCIV in the MTS group was about 44 mm2 less than that in the non-MTS group (P < 0.01). The following factors may be responsible for the decreased reference LCIV area in MTS; first, both previous and present studies have shown a significant positive correlation between BMI and the area of the deep vein; thus, the low proportion of obesity in the MTS group may lead to the decrease of reference LCIV area. Second, the LCIV and left common iliac artery were extraordinarily close to each other in some MTS cases, which results in partial compression of middle or distal LCIV. Although this compression did not reach the degree of severe stenosis,[21] it would reduce the area of the middle and distal LCIV.[22] The high inconsistency of reference LCIV area in the MTS group that was found in the current study may also be related to the above factor. The reason for the decrease of reference LCIV area in MTS remains to be determined. Nevertheless, the above findings provide a reference for more precise determination of the MTS stenosis and selection of the appropriate stent size.

In clinical practice, the selection of stent size should not be limited to the fixed vein reference area, and the variability of vein area should be fully considered. One of the significant differences between veins and arteries is that the walls of veins are much more compliant. Compared with the relatively-fixed circular lumen of arteries, the shape of the cross-sectional area of veins is often more variable. Raju et al. mentioned that the optimum stent size to achieve the best hemodynamic improvement is the positive circular area when the perimeter of the LCIV is constant.[9] As a result, choosing the positive circle area under the same perimeter of LCIV as the reference for the selection of stent size may improve the symptoms of patients with MTS more effectively. In addition, there are significant differences in vein area among different populations, especially for people with higher BMI and larger stent size and more aggressive treatment strategies should be suitable for these population. Barbati et al. found that larger stent size has a significant positive influence on stent patency rates because stent occlusion appears to be related to the slowly narrowing of the stent lumen over time.[23] As a result, A selection of a larger nominal diameter stent during the initial intervention may help prevent stent occlusion.

This study has a few limitations. One of the limitations of current study may be the possible variation in the vein area with patient's respiratory cycle or hydration status because the CT scan was performed with the patients in the supine position. Although this deviation cannot be completely avoided, it can be minimized by instructing the patient to breathe calmly and maintain a normal diet during the examination.[24] Other limitations include small sample size originating from local institutions, deficiencies of patient baseline differences in retrospective control study, and the inability of CTV to assess hemodynamics and endovenous lesions.[25] Nevertheless, this study contributes to a small body of literature suggesting that the area of reference LCIV is related to many factors. It also reports significant differences in area and variability between the patient with or without MTS.


  Conclusions Top


The normal anatomic area of LCIV is defined and affected by many factors. There was a significant correlation between the increase of LCIV area and BMI, but not with gender, age, and symptoms. More importantly, patients with MTS had more variability in LCIV area compared with patients without MTS, although the area of LCIV was smaller in the MTS group.

Acknowledgments

This study is supported by the Chinese national natural science foundation (No. 8167440) and Clinical Research Program of 9th People's Hospital, Shanghai Jiao Tong University School of Medicine (JYLJ026).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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