|Year : 2020 | Volume
| Issue : 4 | Page : 111-118
The beneficial role of intravascular ultrasound in the diagnosis and treatment of nonthrombotic iliac venous obstructions as compared with traditional venography in the Chinese population
Yong Ding, Min Zhou, Liang Cai, Xu Li, Tianchen Xie, Fen Yu, Daqiao Guo, Zhenyu Shi
Department of Vascular Surgery, Zhongshan Hospital, Institute of Vascular Surgery, Fudan University, Shanghai, China
|Date of Submission||21-Jul-2020|
|Date of Acceptance||24-Aug-2020|
|Date of Web Publication||24-Dec-2020|
Dr. Daqiao Guo
Department of Vascular Surgery, Zhongshan Hospital, Institute of Vascular Surgery, Fudan University, 180 Fenglin Road, 200032 Shanghai
Dr. Zhenyu Shi
Department of Vascular Surgery, Zhongshan Hospital, Institute of Vascular Surgery, Fudan University, 180 Fenglin Road, 200032 Shanghai
Source of Support: None, Conflict of Interest: None
PURPOSE: The efficacy of intravascular ultrasound (IVUS) in diagnosing obstructive venous lesions has been established in the Western countries; however, its beneficial role in the Asian population is seldom reported. Because IVUS is still not widely used in China, we, therefore, investigated whether the salutary effect of IVUS on the diagnosis and treatment of iliac venous outflow obstructions could also be extended to the Chinese population.
MATERIALS AND METHODS: This was a prospective single-center study. Patients with nonthrombotic iliac venous obstructions were consecutively enrolled from September 2017 to September 2019. IVUS and venography were performed for every participant. The anatomic characteristics of the venous lesions were measured by these two imaging modalities and then compared with each other. Venous lesions were divided into the collateral and noncollateral group according to the presence of collaterals on venographic images, and comparison was performed between the two groups. The difference of lesion diameter or area at the most compression site was also observed after the endovascular intervention.
RESULTS: A total of 50 patients with 59 limbs were eligible (males, 25; females, 25; mean age 63.46 ± 8.07). The clinical-etiology-anatomy-pathophysiology classification was C4: 43 (72.88%), C5: 6 (10.17%), and C6: 10 (16.95%). Compared with IVUS, the diameter and area stenosis calculated by traditional venography were dramatically lower than that measured by IVUS (diameter stenosis, 38.56% ± 17.76% vs. 64.55% ± 15.96%, P < 0.001; area stenosis: 51.14% ± 19.50% vs. 60.11% ± 13.86%, P = 0.003). Based on a previously reported 50% stenosis threshold (significant stenosis), traditional venography displayed a low sensitivity of 23.91% and an acceptable specificity of 84.62% in detecting significant lesions. The overall intermodality agreement was extraordinarily low between venography and IVUS (κ = 0.045). With no major difference in the baseline characteristics, the area stenosis measured by IVUS was not significantly different between the collateral and noncollateral group (61.31% ± 15.29% vs. 57.94% ± 10.79%, P = 0.376). IVUS also confirmed a significant increase of the compressed vein lumen after the endovascular intervention.
CONCLUSIONS: Compared with IVUS, traditional venography underestimates the degree of stenosis and misses significant iliac venous obstructive lesions. The collaterals presented by venography is not a reliable indicator in distinguishing significant lesions. IVUS is a valuable and effective imaging modality in the diagnosis and treatment of nonthrombotic iliac venous obstructions in the Chinese population.
Keywords: Intravascular ultrasound, nonthrombotic iliac venous obstructions, traditional venography
|How to cite this article:|
Ding Y, Zhou M, Cai L, Li X, Xie T, Yu F, Guo D, Shi Z. The beneficial role of intravascular ultrasound in the diagnosis and treatment of nonthrombotic iliac venous obstructions as compared with traditional venography in the Chinese population. Vasc Invest Ther 2020;3:111-8
|How to cite this URL:|
Ding Y, Zhou M, Cai L, Li X, Xie T, Yu F, Guo D, Shi Z. The beneficial role of intravascular ultrasound in the diagnosis and treatment of nonthrombotic iliac venous obstructions as compared with traditional venography in the Chinese population. Vasc Invest Ther [serial online] 2020 [cited 2021 Jul 27];3:111-8. Available from: https://www.vitonline.org/text.asp?2020/3/4/111/304840
| Introduction|| |
Nonthrombotic iliac venous obstruction can cause significant hemodynamic alterations, which might lead to subsequent acute deep vein thrombosis or chronic venous insufficiency. The diagnosis and accurate anatomic measurements underlie the endovascular treatment of obstructive venous lesions. However, the frequently elliptical or irregular shape of iliac veins increases the difficulty in detecting and quantifying stenotic venous lesions.
Traditional venography and emerging intravascular ultrasound (IVUS) are two commonly used modalities in diagnosing and evaluating obstructive venous disease. In recent years, IVUS has been widely applied in patients with iliac vein compression, owing to its superior ability in accurately evaluating venous stenosis. In addition to the reduced radiation exposure, IVUS also has the advantage of direct visualization of the surrounding tissues as well as the intraluminal structures such as web, spur, or trabeculation. These advantages collectively contributed to the rapidly increased application of IVUS in the Western world. However, currently, the use of IVUS in obstructive venous lesions is still very limited in China (only in a few centers). This might be related to the unavailability of IVUS instruments in most centers and also the increased cost caused by IVUS. In contrast, traditional venography remains the mainstream in the intraoperative evaluation of obstructive venous lesions in China. Compared with IVUS, venography is less expensive and more accessible, even with a relatively low sensitivity of identifying stenosis. The hemodynamic information provided by venography, such as collaterals, is also a nonnegligible factor to be considered when treating obstructive venous lesions. As researches focusing on the comparison between traditional venography and IVUS are seldomly reported in Asia, we, therefore, investigated whether the beneficial role of IVUS could also be extended to the iliac venous outflow obstructions in the Chinese population.
| Materials and Methods|| |
This was a prospective, single-center cohort study and had been approved by the Ethics Committee of Zhongshan Hospital, Fudan University (Shanghai, China). Patients with severe chronic venous insufficiency (clinical-etiology-
anatomy-pathophysiology [CEAP] 4–6) who were considered with suspicious iliac venous outflow obstructions were consecutively enrolled into this study from September 2017 to September 2019. This research had been registered in www.clinicaltrials.gov (NCT03309969). The detailed inclusion and exclusion criteria of this study were listed on the website. Briefly, the major inclusion criteria were: (1) Suspicious or confirmed iliac venous obstructions as detected by preoperative magnetic resonance venography (MRV) or computed tomographic venography (CTV); (2) patent common femoral and femoropopliteal vein of the target limb (confirmed by Doppler ultrasound). The major exclusion conditions were: (1) Venous compression caused by pelvic tumors or fibroid uterus; (2) previous stent implantation or venous bypass surgery of the target limb; (3) iodine allergy or severe renal insufficient function; (4) acute deep vein thrombosis or postthrombotic syndrome involving the target limb. Besides, patients with evident venous reflux (reflux time >1 ms under ultrasonography) were also excluded because endovascular treatment for venous obstruction might provide little benefit in these patients.
Transfemoral venography was performed under local anesthesia with a supine position. The ipsilateral common femoral approach was used to perform iliocaval venograms, and in a few cases involving both lower limbs, bilateral femoral veins were accessed. Iodinated contrast medium (Omnipaque, 350 mg I/ml, GE Healthcare, Cork, Ireland) was routinely administered at a rate of 8 ml/s and a pressure of 300 psi. In order to increase the sensitivity of traditional venography, multiple venograms with different projections were performed, including anteroposterior (AP), left anterior oblique (LAO) 45-degree, and right anterior oblique (RAO) 45-degree [Figure 1]. Venographic images were conducted using a standard angiographic system (Axiom Artis; Siemens Healthcare, Forchheim, Germany) and were recorded at an interval of 6 photographs per second. Two independent reviewers interrogated these cine images and measured the diameter at the most compression site (minimal vessel diameter [MVD]) and its distal normal segment (reference vessel diameter, RVD). Among three venograms (AP, LAO 45, RAO 45), the venogram, which displayed the most severe degree of stenosis, was used to calculate the diameter stenosis according to the formula: (1 − MVD/RVD) × 100%. Since the cross-sectional areas could not be directly measured by traditional venography due to its two-dimensional nature, we assumed the venous lumen as an ellipse and then calculated the estimated area according to the vessel diameter measured from two orthogonal projections (LAO 45 and RAO 45). The area of the venous lumen was calculated by using π × (a/2) × (b/2) (a and b were the measured diameters from venogram of LAO 45 and RAO 45); then, the area stenosis could be obtained from the estimated minimal vessel area (MVA) and the reference vessel area (RVA): (1 − MVA/RVA) × 100%.
|Figure 1: Intravascular ultrasound detected a severe nonthrombotic iliac venous lesion (red arrow) which was presented as a mild to middle stenosis on traditional venography (white arrowhead). (a-c) Venograms of left anterior oblique 45, anteroposterior, and right anterior oblique 45; (d-f) The intravascular ultrasound images at the proximal, stenosis, and distal segment of obstructive venous lesions|
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Intravascular ultrasound evaluation
IVUS was performed by using Volcano s5 Imaging System and a PV 0.035 IVUS Catheter (Volcano, CA, USA). The whole iliocaval venous segment was investigated to recognize and localize the exact venous compression site. Recorded IVUS images were reviewed by two independent investigators and indistinct cases were reevaluated by a third reviewer. Different from traditional venography, we could directly measure the diameter or area of the venous segment on IVUS with the built-in software. Then, the diameter or area stenosis was calculated using the same formula as described in venography. Besides, we also marked the most compression site and whole lesion according to IVUS to facilitate the following iliac venous balloon venoplasty and stenting.
IVUS images were analyzed during the procedure to quantify the actual area stenosis of obstructive venous lesions. Patients with significant stenosis (area stenosis ≥50%) underwent subsequent endovascular venoplasty and stenting, while the rest of patients with nonsignificant compressions were recommended with conservative therapies. The size of the balloon and stents were chosen based on the RVD (distal to the compression lesion) measured by IVUS. Meanwhile, the length of venous lesion could also be assessed by the IVUS catheter, and accordingly, appropriate stents were selected to perform endovascular recanalization. Once the stent was successfully deployed and postdilated, completion venogram and IVUS were conducted to evaluate the improvement of blood flow and the enlargement of iliac compression lesions. The anatomic characteristic of venous lesion after stent implantation was compared with its counterpart before intervention as displayed by IVUS.
For continuous variables, outcomes were presented as mean value and standard deviation; for categorical variables, data were presented as frequencies and percentages. The anatomic characteristics measured by traditional venography and IVUS were compared with each other by using paired t-test or Wilcoxon signed-rank test, where appropriate. In comparison between the collateral and noncollateral group, Student's t-test, Man–Whitney U-test, or Chi-square test were employed to examine their difference. The agreement of venography and IVUS for depicting a >50% significant stenosis was tested using Cohen's κ test. To evaluate the improvement of venous lumen, we also compared the anatomic characteristics of the lesion before and after stent deployment by using paired t-test or Wilcoxon signed-rank test. A P < 0.05 was recognized as statistical significance. All statistical analysis was performed with the SPSS Statistics version 23 (IBM, Armonk, NY, USA).
| Results|| |
A total of 50 participants with 59 limbs were enrolled in this study. The average age was 63.46 ± 8.07 years (range, 43–84) and 25 patients were female. Of these, 33 limbs (66.00%) were left-sided and 9 patients presented bilateral lesions. The CEAP classification was C4: 43 (72.88%), C5: 6 (10.17%), and C6: 10 (16.95%). Patient demographics and lesion characteristics are listed in [Table 1]. Left common iliac vein (62.5%) was the most popular compression site.
The anatomic characteristics of the venous lesions, as measured by traditional venography and IVUS, were compared with each other [Table 2]. The MVD was 2.68-fold higher measured by venography than that measured by IVUS (8.04 ± 2.63 mm vs. 3.57 ± 1.60 mm, P < 0.001), while the RVD was also increased but to a lesser extent (1.32-fold, 13.30 ± 3.35 mm vs. 10.52 ± 2.59 mm, P < 0.001). Similarly, the minimal and RVA were also higher as detected by venography (both P < 0.01). Although the vessel diameter and area were markedly increased on venography than on IVUS, the diameter stenosis and area stenosis measured by venography were much lower than that measured by IVUS (diameter stenosis, 38.56% ± 17.76% vs. 64.55% ± 15.96%, P < 0.001; area stenosis: 51.14% ± 19.50% vs. 60.11% ± 13.86%, P = 0.003).
|Table 2: The anatomic measurements detected by venography and intravascular ultrasound before intervention|
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Consistent with previous publications,, a more than 50% stenosis was defined as significant lesions. Among 59 limbs, IVUS revealed significant iliac venous obstructive lesions in 46 limbs (area stenosis ≥50%) and nonsignificant stenosis in 13 limbs. Based on the diameter stenosis measured by traditional venography, 35/46 significant lesions (76.09%) were totally missed even with multiple projections (diameter stenosis < 50%), and two nonsignificant lesions (15.38%) were misdiagnosed compared with IVUS [Figure 2]a. Under such a scenario, the sensitivity and specificity of traditional venography in identifying significant lesions were 23.91% and 84.62% as compared with IVUS. Moreover, the intertechnique agreement between venography and IVUS was extremely slight [κ = 0.045, [Figure 2]a. By contrast, based on the estimated area stenosis measured by traditional venography, only 17/46 significant lesions (36.96%) were missed, and four nonsignificant lesions (30.77%) were misjudged, leading to improved sensitivity of 63.04% and a reduced specificity of 69.23% [Figure 2]b. The intermodality agreement did increase but remained relatively low [κ = 0.238, [Figure 2]b.
|Figure 2: The comparison between venography and intravascular ultrasound in detecting significant lesions. (a) Base on diameter stenosis, venography missed the majority of significant lesions which were detected by intravascular ultrasound; (b) When the estimated area stenosis was used, venography displayed an improved intermodality agreement with intravascular ultrasound in identifying significant lesions|
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According to the presence of collaterals on venograms, the subjects were divided into the collateral and noncollateral group [Figure 3]. The majority of involved limbs (38/59, 64.41%) displayed obvious venous collaterals on venograms while the rest (21/59, 35.59%) did not. Baseline conditions such as age, sex, body mass index, lesion side, and CEAP score were similar between the two groups [Table 3]. On traditional venography, no major difference was found between the two groups, including the minimal and RVD, the estimated minimal and RVA, and the diameter stenosis. However, the collateral group tended to display higher estimated area stenosis compared with the noncollateral group (54.59% ± 18.29% vs. 44.91% ± 20.50%, P = 0.067). With regard to IVUS, it did not find a significant difference in RVD, MVA, or RVA between the two groups; however, IVUS discovered a lower MVD (3.32 ± 1.62 mm vs. 4.04 ± 1.49 mm, P = 0.033) and a higher degree of diameter stenosis (67.48% ± 17.04% vs. 59.26% ± 12.48%, P = 0.010) in the collateral group. However, the area stenosis, a more important index in evaluating the degree of obstruction, was not significantly different between the two groups (61.31% ± 15.29% vs. 57.94% ± 10.79%, P = 0.376). This indicated that the degree of stenosis was not actually different between the collateral and noncollateral groups as confirmed by IVUS.
|Figure 3: The presence of collaterals on venogram was not a reliable indicator of significant stenosis as confirmed by intravascular ultrasound. (a-c) A iliac venous lesion from the collateral group displayed a nonsignificant stenosis on intravascular ultrasound (red arrow); (d-f) An obstructive venous lesion from the noncollateral group demonstrated a severe iliac venous compression from the adjacent artery as confirmed by intravascular ultrasound (white arrow)|
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|Table 3: The comparison between the collateral and the noncollateral group|
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A total of 49 patients with 56 limbs accepted endovascular treatment. As shown in [Table 4], IVUS detected a marked increase of the MVD and area at the most compression site, while the enlargement of RVD and area were much slighter. And as expected, stenting resulted in a prominent drop of the area stenosis from 61.74% to 14.22% after stent deployment, concomitant with the reduced diameter stenosis (both P < 0.001). At 6 months, 46 patients (93.88%) with 53 limbs completed their follow-up visit and 40 patients (86.96%) with 47 limbs reported an improvement of symptoms in the lower limb. The mean CEAP score of these 47 limbs decreased from 4.55 ± 0.83 to 4.45 ± 0.69 (P = 0.025) at 6 months after surgery.
|Table 4: The anatomic characteristics of target lesions before and after endovascular intervention as delineated by intravascular ultrasound|
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| Discussion|| |
The low sensitivity of traditional venography in evaluating stenotic venous lesions have already been documented, whereas it remains widely used in endovascular procedures due to its easy accessibility. Recently, the VIDIO trial confirmed the superiority of IVUS in the detection and quantification of iliac venous obstructions compared with multiplanar venography. However, whether the beneficial effect of IVUS could be extended to the obstructive venous lesions in Asians, whose vasculature is potentially different from the Westerners, remains as a question. Therefore, this study focused on this issue and demonstrated that traditional venography not only underestimated the degree of stenosis but also missed significant obstructive venous lesions compared with IVUS. Besides, the collaterals displayed by venography, which was believed to be an important hemodynamic feature of severe stenosis, was not a reliable indicator of significant stenosis. In summary, our study verified a highly valuable role of IVUS in assessing iliac venous obstructions in a Chinese patient cohort.
Compared with IVUS, traditional venography identified a significantly larger vessel diameter at the most compression site and the distal normal segment. The larger diameter measured by venography could be ascribed to the two-dimensional feature produced by projection. It is hard for traditional venography to be exactly projected from a view which is perpendicular to the shortest diameter; therefore, the measured diameter would be overestimated in most situation, even with multiplanar venography. Notably, the MVD was 2.68-fold increased while the RVD was only 1.32-fold increased as detected by venography. This indicated that venography would amplify the diameter to a greater extent for a more stenotic lumen. This deduction was supported by the significant correlation between the fold change of diameter (MVDvenography/MVDIVUS) and the area stenosis measured by IVUS (r = 0.257, P = 0.049). This intriguing correlation leads to a markedly underestimated diameter stenosis measured by venography than that measured by IVUS. Similarly, the area stenosis was also undervalued by traditional venography when the MVA was overestimated to a higher degree than that of RVA. These results collectively suggested that the degree of stenosis was significantly underestimated by traditional venography.
Identifying which lesion needs to be treated is far more important than quantifying the degree of stenosis. In consistent with previous publications,, venous lesions of more than 50% stenosis are recognized as significant lesions, which could result in symptom improvement when stented. Based on this threshold, traditional venography missed as much as 76.09% significant lesions and resulted in low sensitivity of 23.91% according to the measured diameter stenosis. This rate is concordant with the reported 72% of patients who were failed to be detected with a significant lesion under three-view venography in VIDIO trial. By contrast, when the estimated area stenosis calculated by venography was used, the sensitivity of identifying significant lesions increased to a more acceptable level (63.04%), and intermodality agreement with IVUS was also improved. This suggested a critical role of the estimated area stenosis measured by venography in recognizing significant lesions if IVUS was not available. We tried to combine the diameter stenosis and estimated area stenosis measured by venography to better distinguish significant lesions. However, this combination did not improve the sensitivity or specificity of traditional venography. Therefore, IVUS was highly recommended if it is available, in order to accurately quantify the degree of stenosis and recognize significant lesions which would benefit from endovascular interventions. The estimated area stenosis, rather the diameter stenosis measured by venography, is a more appropriate index in distinguishing significant lesions when IVUS is not available.
Collaterals have been viewed as an important feature of obstructive venous lesions. In the past decades when IVUS was not commercially available, stenotic venous lesions were delineated by traditional venography based on the presence of collaterals, translucency, and contrast stagnation. The presence of evident collaterals was probably linked to a higher degree of stenosis. However, contrary to this intuition, the lesion area, the RVA, and the area stenosis, as measured by IVUS, did not significantly different between the collateral and noncollateral group. In contrast, the estimated area stenosis measured by venography, tended to be higher in the collateral group, which did also reflect the unreliability of venography in evaluating obstructive venous lesions as compared with IVUS. Together, our results suggested that the presence of collaterals alone was not efficient in distinguishing significant stenotic lesions. Some researchers might argue that the combination of diameter (or area) stenosis measured by venography with the presence of collaterals could improve the sensitivity or specificity. This combination did increase the specificity, but also reduced the sensitivity of venography in detecting significant lesions. Supplementary tools such as venous pressure gradient measurements or IVUS were needed to improve the diagnostic accuracy of venography in identifying significant venous stenosis.
Other imaging modalities have also been applied in the detection of iliac venous compressions such as Doppler ultrasound, MRV, and CTV. The deep location of iliac veins and the extraordinary dependence on experiences limited the use of Doppler ultrasound in diagnosing iliac venous stenosis.,,, Hence, we only used the Doppler ultrasound to rule outpatients with acute deep vein thrombosis who might need a different treatment such as anticoagulation, catheter-directed thrombolysis, or pharmacomechanical thrombolysis. It has also been reported that MRV displayed a high sensitivity but a low specificity in diagnosing proximal venous outflow obstructions. However, MRV sequences have been shown to be unstable over time and therefore, might be insufficient to diagnose nonthrombotic iliac venous lesions. Another powerful method in screening and classification of iliac venous obstruction was CTV, which demonstrated a high intermodality agreement with IVUS in determining the precise point of compression. Nonetheless, these imaging tools were not applicable in the intraoperative evaluations, and therefore were only used as screening methods to enroll patients with suspicious iliac venous obstructions in our study. Consequently, the comparison of venography or IVUS with these modalities was not performed in this research.
IVUS was also helpful in evaluating the improvement of the compressed venous lumen after stent implantation. Our data displayed a significant reduction of the area stenosis after endovenous recanalization, indicating the efficacy of stenting in treating stenotic venous lesions. By contrast, it was less clear on traditional venography to evaluate the residual stenosis because the measured diameter stenosis might be inaccurate, and the presence of collaterals was not a reliable indicator as mentioned above. Therefore, using IVUS to reevaluate the whole iliocaval segments after stent deployment was necessary to verify the effect of endovascular treatment and to rule out obvious residual stenosis, which might need additional interventions to correct it.
Although endovascular treatment worked well in the majority of our patients at follow-up, it did not lead to significant improvement of symptoms in some patients. Appropriate patient selection was, therefore, necessary to achieve a satisfactory outcome. It should be noticed that approximately 20% of the normal population have a common iliac vein compression >70%. Hence, the area stenosis measured by IVUS should not be used as the only reference in the decision-making for intervention. Supplementing IVUS findings with hemodynamic measurements of reflux and outflow resistance was helpful in distinguishing patients with or without well-developed collateral circulations. The risk of overtreatment could be reduced with these additional measures.
This study corroborated the superior role of IVUS in detecting and quantifying iliac venous obstructions in comparison with traditional venography, in a Chinese patient cohort. However, several limitations should be noticed. First, this was a prospective single-center cohort study which only included Chinese patients. Hence, the conclusion of our research should be applied and generalized cautiously. Second, the sample size was relatively small, and further larger registries are warranted to confirm our results.
| Conclusions|| |
In the Chinese population, compared with IVUS, traditional venography underestimates the degree of stenosis and misses significant obstructive iliac venous lesions. The collaterals presented by venography alone is not a reliable indicator in diagnosing significant lesions. IVUS is a valuable and effective imaging modality in the diagnosis and treatment of nonthrombotic iliac venous outflow obstructions.
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Conflicts of interest
There are no conflicts of interest.
| References|| |
Kim JY, Choi D, Guk Ko Y, Park S, Jang Y, Lee DY. Percutaneous treatment of deep vein thrombosis in May-Thurner syndrome. Cardiovasc Intervent Radiol 2006;29:571-5.
Gagne PJ, Tahara RW, Fastabend CP, Dzieciuchowicz L, Marston W, Vedantham S, et al
. Venography versus intravascular ultrasound for diagnosing and treating iliofemoral vein obstruction. J Vasc Surg Venous Lymphat Disord 2017;5:678-87.
Shebel ND, Whalen CC. Diagnosis and management of iliac vein compression syndrome. J Vasc Nurs 2005;23:10-7.
Neglén P, Raju S. Intravascular ultrasound scan evaluation of the obstructed vein. J Vasc Surg 2002;35:694-700.
Gagne PJ, Gasparis A, Black S, Thorpe P, Passman M, Vedantham S, et al
. Analysis of threshold stenosis by multiplanar venogram and intravascular ultrasound examination for predicting clinical improvement after iliofemoral vein stenting in the VIDIO trial. J Vasc Surg Venous Lymphat Disord 2018;6:48-560.
Hager ES, Yuo T, Tahara R, Dillavou E, Al-Khoury G, Marone L, et al
. Outcomes of endovascular intervention for May-Thurner syndrome. J Vasc Surg Venous Lymphat Disord 2013;1:270-5.
Toh MR, Tang TY, Lim HH, Venkatanarasimha N, Damodharan K. Review of imaging and endovascular intervention of iliocaval venous compression syndrome. World J Radiol 2020;12:18-28.
Butros SR, Liu R, Oliveira GR, Ganguli S, Kalva S. Venous compression syndromes: Clinical features, imaging findings and management. Br J Radiol 2013;86:20130284.
Oğuzkurt L, Ozkan U, Tercan F, Koç Z. Ultrasonographic diagnosis of iliac vein compression (May-Thurner) syndrome. Diagn Interv Radiol 2007;13:152-5.
Arnoldussen CW, Toonder I, Wittens CH. A novel scoring system for lower-extremity venous pathology analysed using magnetic resonance venography and duplex ultrasound. Phlebology 2012;27 Suppl 1:163-70.
Kayılıoğlu SI, Köksoy C, Alaçayır İ. Diagnostic value of the femoral vein flow pattern for the detection of an iliocaval venous obstruction. J Vasc Surg Venous Lymphat Disord 2016;4:2-8.
Massenburg BB, Himel HN, Blue RC, Marin ML, Faries PL, Ting W. Magnetic resonance imaging in proximal venous outflow obstruction. Ann Vasc Surg 2015;29:1619-24.
McDermott S, Oliveira G, Ergül E, Brazeau N, Wicky S, Oklu R. May-Thurner syndrome: Can it be diagnosed by a single MR venography study? Diagn Interv Radiol 2013;19:44-8.
Rossi FH, Kambara AM, Rodrigues TO, Rossi CB, Izukawa NM, Pinto IM, et al
. Comparison of computed tomography venography and intravascular ultrasound in screening and classification of iliac vein obstruction in patients with chronic venous disease. J Vasc Surg Venous Lymphat Disord 2020;8:413-22.
Nazzal M, El-Fedaly M, Kazan V, Qu W, Renno AW, Al-Natour M, et al
. Incidence and clinical significance of iliac vein compression. Vascular 2015;23:337-43.
Nicolaides OM, Lugli M, Guerzoni S. Noninvasive measurement of lower limb outflow resistance and implications for stenting. Vascular Invest Ther 2019;2:88-94.
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]