Frequency of left common iliac vein compression in asymptomatic adolescents and young adults

Abstract

Objective

Venous compression at the iliac confluence is a reported risk factor for deep vein thrombosis, with venous stenting as the standard management for relieving this compression. Kibbe et al demonstrated that left common iliac vein (LCIV) compression is present in 35.3% of asymptomatic patients. However, this study included only adults with an average age of 40 years. The iliac vein confluence in patients under 21 years with no symptoms attributable to venous disease was evaluated in this study. The study goal is to determine prevalence of LCIV narrowing in patients under age 21 years, and as such, assist in determining the appropriate treatment for iliac vein compression in this patient population.

Methods

A retrospective review of patients aged 13-20 undergoing abdominal/pelvic computed tomography (CT) imaging for nonvascular indications was performed. This group was compared with patients aged 35 to 65 years undergoing CT imaging for similar reasons. Axial CT images were reviewed by two independent examiners to identify the diameter of the noncompressed left and right CIVs below the confluence and the diameter of the LCIV at the site of compression between the right common iliac artery and spine.

Results

A total of 122 patients aged 13 to 20 years were identified with high-quality CT imaging and no venous symptoms for image review. Mean LCIV diameter was 12.7 ± 2.5 mm, and mean right CIV diameter was 13.1 ± 2.2 mm. The diameter of the LCIV at the confluence was 4.2 ± 1.8 mm, resulting in a mean diameter stenosis of the LCIV of 69.4% ± 12.6%. In this population, 55.7% of patients were found to have ≥70% stenosis of the LCIV on CT imaging compared with 1.7% of patients aged 35 to 65 years (P < .001). There was no statistical difference in the percentage of LCIV stenosis in young patients based on body mass index, gender, race, or ethnicity.

Conclusions

Severe compression of the LCIV at the iliac confluence was identified in over 50% of asymptomatic patients aged 13 to 20 years on CT imaging performed for nonvascular reasons. This suggests that narrowing of the LCIV is a normal anatomic finding in this age group. The incidence of severe compression is significantly lower in older asymptomatic persons. In young persons, the high incidence of iliac vein compression on CT imaging suggests that this finding may not be a significant risk factor for deep vein thrombosis or limb symptoms, questioning the need for routine intervention for compression correction in this patient population.

Article Highlights.

• •Type of Research: Retrospective case series
• •Key Findings: Abdominal/pelvic computed tomography scans performed on 122 patients aged 13 to 20 years for nonvenous symptoms were reviewed to identify the severity of iliac venous compression at the iliac confluence. The mean left common iliac vein compression was found to be 69.4%. The severity of compression was significantly greater than in 60 patients aged 35 to 65 years in whom the mean left common iliac vein compression was 37.2%.
• •Take home Message: On computed tomography imaging of the abdomen and pelvis, severe compression of the left common iliac vein is seen in the majority of patients aged 13 to 20 years, suggesting that this is a normal anatomic variant in this age group.

The presence of compression of the common iliac veins (CIVs) at the iliac confluence has been described for over a century.¹ May and Thurner identified iliac vein compression to be a cause of pathologic changes within the lumen of the vein.² This was suggested to be the cause of the clinical observation that deep vein thrombosis (DVT) occurs more frequently in the left leg.^3,4 This has led to practice guidelines recommending venous stenting after thrombus removal to eliminate outflow obstruction, thereby reducing the incidence of recurrent thrombosis.⁵

Kibbe et al studied the presence of left common iliac vein (LCIV) compression in asymptomatic patients using computed tomography (CT), reporting an average compression of 35.5%.⁶ Compression greater than 50% was identified in 24% of patients. Other authors have confirmed these findings.⁷ Consensus on the degree of nonthrombotic iliac vein compression that should warrant intervention with stenting has been difficult to achieve.⁸ The VIDIO trial reported that patients demonstrate improved clinical benefit with intervention when the degree of narrowing is greater than 61%.⁹ But other authors note there is limited evidence to support any threshold for compression and its relationship to symptoms, suggesting that it is overly simplistic to relate a single area of venous stenosis to patient symptoms.¹⁰ In a 2019 review, Harbin and Lutsey highlighted the difficulty in assessing iliac vein compression as a risk factor for DVT, given the lack of epidemiologic data on its prevalence.⁸ They suggested that research defining the prevalence of LCIV compression in asymptomatic patients over a wide age range would be useful in determining its magnitude as a risk factor for DVT.

There is greater uncertainty concerning treatment of young patients with iliac vein compression who present with leg symptoms or proximal DVT. Patients under the age of 21 years are under-represented in studies of iliac vein compression with little information in the literature describing the normal anatomy of the pelvic venous outflow in adolescents and young adults. It is currently unclear whether the finding of iliac vein compression is clinically relevant in patients undergoing evaluation of the abdominal and pelvic veins with abdominal/pelvic imaging. Previous studies reporting on the presence of iliac vein compression were performed in adults with few patients younger than 21 years represented.^6,7 In a prospective study evaluating iliac vein compression in 20 asymptomatic patients ages 20 to 22 years, 80% of patients had two signs of iliac vein compression on venography.¹¹ This present study evaluated pelvic venous anatomy of patients between 13 and 20 years undergoing CT of the abdomen and pelvis (CT AP) for nonvenous symptoms to identify the normal pelvic venous anatomy in this population.

Methods

Using a retrospective database of patients undergoing cross-sectional imaging between 2018 and 2024, candidates previously studied with CT AP using intravenous contrast were identified. Patients with no prior history of venous insufficiency or DVT who were undergoing CT for symptoms unrelated to the lower extremities were selected for review. Most patients were studied for abdominal pain, limited trauma, or abdominal mass. Those with iliac vein or inferior vena cava (IVC) atresia, duplicate IVC, or other anatomic variations of the pelvic venous system were excluded from the study. Patients with retroperitoneal lesions, severe multisystem trauma, or severe infection/sepsis were excluded. To attempt to avoid patients with severe dehydration, those with atypically collapsed iliac veins and/or IVC were also excluded. Other exclusions included patients with acute exacerbations of chronic conditions including congestive heart failure, chronic obstructive pulmonary disease, renal or hepatic failure, and those with disseminated oncologic conditions. Patient records were reviewed to identify demographic factors (sex, race, ethnicity) and body mass index (BMI). Two age groups were selected for comparison, with the younger group aged 13 to 20 years and an older group aged 33 to 67 years.

Measurement of iliac vein compression

CT AP imaging was reviewed in multiple planes. Comparing coronal images linked side by side with axial images, the course of the iliac veins at the venous confluence was identified. The LCIV was followed as it crossed over the lumbar vertebrae behind the aortic bifurcation to join the right CIV (RCIV) forming the IVC. The site of maximal narrowing of the LCIV through its course was identified using both imaging planes; it was separately measured on sagittal plane for consistency (Fig 1). At this site, the diameter of the compressed vein was measured in an anterior-posterior dimension. The CIV was followed on axial imaging moving caudally, and an uncompressed segment of the vein was identified just above the confluence of the internal and external iliac veins where the CIV diameter was again measured (Fig 2). Compression percentage was calculated by dividing the difference between the uncompressed and compressed LCIV measurements by the uncompressed LCIV. The RCIV was also examined to compare with the LCIV and identify compression if present. Measurements and calculations were performed by two independent examiners for each CT study. One of the examiners was a board-certified vascular surgeon or interventional radiologist, and the other was a vascular surgery or interventional radiology resident. The average compression percentage of the two reads was used in the final statistical analysis. If a discrepancy >15% was found in compression percentage between the two examiners, a third set of measurements and calculations was performed by a board-certified radiologist. The two closest measurements were averaged to achieve the final compression percentage in these cases.

Fig 1.

Identifying the point of maximal compression of the iliac veins at the venous confluence. (A) Using coronal view to identify location where aorta and/or iliac arteries cross over the iliac veins at the venous confluence. (B) Identifying point of maximal venous compression between the aorta and/or iliac arteries and the anterior aspect of the vertebra.

Fig 2.

Identifying non-compressed segment of common iliac vein (CIV) distal to point of compression for measurement. LCIV, Left common iliac vein.

The primary outcomes measured were the mean percentage compression of the LCIV, as well as the frequency of LCIV compression greater than 50% and greater than 70%. These measures were compared between the two age groups. Further subgroup analyses based on patient demographics and BMI were performed.

Statistical analysis

We analyzed population level and age-specific (young vs old) demographics and percent venous compression. Continuous variables (age, BMI, and percent compression) were analyzed using Student’s t-tests and listed as mean ± standard deviation, unless otherwise specified, and compared across groups. Categorical variables (sex, race, and ethnicity) were analyzed using χ² tests and reported as number (%). Race was missing for six individuals (3 young and 3 old). We further explored the mean percent compression by age within BMI, sex, race, and ethnicity groups. BMI was represented as a binary variable (<25 kg/m² or ≥25 kg/m²) based on the American Heart Association's definition of “normal” BMI; sex was binary as assigned in the electronic medical record (male or female); race was categorized as White, Black, or other; and ethnicity was binary (Hispanic or non-Hispanic). BMI, sex, and ethnicity were compared using Student’s t-tests, whereas race was compared using analysis of variance. All analyses were performed using SAS version 9.4. The Institutional Review Board of the University of North Carolina approved this study and determined informed patient consent was not needed due to the retrospective nature of the study.

Results

The younger group consisted of 121 patients with an age range of 13 to 20 years. The mean age of this group was 17 years, and 62% were female (n = 75). In comparison, the adult control group included 60 patients with an age range 35 to 65 years (mean, 49 years) and were also 62% female. Other demographics and characteristics in the two groups are compared in Table I. In the older group, a higher proportion of patients were Black (P = .034). Older patients also had a significantly higher mean BMI compared with the younger group (P < .001). The indications for CT imaging in each group are listed in Table II. A higher percentage of scans were performed for nonmajor trauma in younger patients and a higher percentage for abdominal mass in older patients. However, these differences were not significantly different. The percentage of scans performed for abdominal pain were similar in each group.

Table I.

Patient demographics in all patients and in each age group

	Total (N = 181)	Young (13-20 years) (n = 121)	Old (35-65 years) (n = 60)	P value young vs old
Age, years	27.6 ± 16.5	16.6 ± 2.3	49.8 ± 8.3	<.001
Female sex	112 (61.9)	75 (62.0)	37 (61.7)	.967
Race				.034
White	95 (54.3)	68 (57.6)	27 (47.4)	--
Black	38 (21.7)	19 (16.1)	19 (33.3)	--
Other	42 (24.0)	31 (26.3)	11 (19.3)	--
Hispanic ethnicity	37 (20.4)	25 (20.7)	12 (20.0)	.917
BMI, kg/m2	28.3 ± 8.8	26.2 ± 8.4	32.3 ± 8.1	<.001

BMI, Body mass index.

Data are presented as number (%) or mean ± standard deviation.

Table II.

Indications for computed tomography of abdominal/pelvic (CT-AP) imaging by patient age group

	Young group (n = 121)		Older group (n = 60)		P value
	No.	% of total	No.	% of total
Abdominal pain	65	53.7%	30	50.0%	.22
Minor trauma	20	16.5%	4	6.7%	.07
Ovarian cyst/uterus	12	9.9%	4	6.7%	.53
Lymph node evaluation	5	4.1%	3	5.0%	.79
Kidney cyst	3	2.5%	5	8.3%	.07
Fever	3	2.5%	3	5.0%	.80
Abdominal mass	4	3.3%	7	11.7%	.03
Other	9	7.4%	4	6.7%	.85

Boldface P values indicate statistical significance.

In young patients, there was no significant difference between the mean diameter of the noncompressed LCIV (12.7 ± 2.5 mm) and RCIV (13.1 ± 2.2 mm). The LCIV diameter was reduced in all studied patients to some degree in its course over the spine to the iliac confluence. The mean minimal diameter of the LCIV through its course was 4.29 ± 1.8 mm when measured on axial imaging. Separate measurement of the minimal CIV diameter on sagittal images was consistent with axial imaging with a mean diameter of 4.28 ± 1.6 mm.

The mean percentage of diameter stenosis of the LCIV in the young patient group was 69.4% ± 12.6% (Fig 3). Mean iliac vein diameters in the older group are compared with the younger group in Table III. The RCIV and uncompressed LCIV are significantly larger in older patients with a mean difference of 1.2 mm and 1.5 mm, respectively. The mean percentage stenosis of the older patient group was significantly less (37.2% ± 19.1%; P < .001) than in the younger group. More than one-half of young patients (n = 68; 55.7%) were found to have ≥70% stenosis of the LCIV, and 93.4% had >50% stenosis. The incidence of iliac vein stenosis at these levels was significantly lower in the older patient group, where 28.3% demonstrated >50% stenosis and only one patient (1.7%) had >70% stenosis (P < .001 for both compared with the young patient group) (Fig 4). Stenosis of the RCIV ≥50% was identified in only two patients in the younger group with none measuring ≥70%.

Fig 3.

Mean percentage compression of the proximal left common iliac vein (LCIV) in the younger patient group (age 13-20 years) compared with the older patient group (age 35-65 years). The difference is statistically significant (P < .001).

Table III.

Mean iliac vein diameters by patient age group

	RCIV diameter	Uncompressed LCIV diameter	P value RCIV vs uncompressed LCIV	Compressed LCIV diameter	Mean % compression
Young patient group	13.1 ± 2.2 mm	12.7 ± 2.5 mm	.69	4.3 ± 1.8 mm	69.4 ± 12.6
Old patient group	14.3 ± 2.6 mm	14.2 ± 2.4 mm	.88	7.9 ± 3.8 mm	37.2 ± 19.1
P value young vs old	<.005	<.005		<.001	<.001

LCIV, Left common iliac vein; RCIV, right common iliac vein.

Fig 4.

Incidence of left common iliac vein (LCIV) compression ≥70% in the young patient group (age 13-20 years) compared with the older patient group (age 35-65 years). The difference is statistically significant (P < .001).

Patient demographics and BMI were collected to determine whether these were correlated with the degree of compression of the LCIV. As detailed in Table IV, there was no correlation between sex, race, ethnicity, or BMI to severity of compression in the younger group. Within the older group, there was a significantly higher degree of LCIV compression identified in women compared with men (P = .015). BMI, race, and ethnicity did not significantly affect the degree of LCIV compression in the older group.

Table IV.

Influence of demographics and body mass index (BMI) on left common iliac vein (LCIV) compression in the young patient group

Risk factor	% compression	P value
BMI, kg/m2		.711
<25	70.0 ± 12.5
>25	69.1 ± 12.9
Gender		.652
Male	70.1 ± 12.3
Female	69.0 ± 12.9
Race		.078
White	67.3 ± 12.9
Black	69.9 ± 12.1
Ethnicity		.324
Hispanic	71.6 ± 12.5
Non-Hispanic	68.8 ± 12.7

Discussion

Compression of the LCIV is frequently identified on CT AP imaging in patients undergoing diagnostic imaging for a wide variety of indications. This often leads to a clinical dilemma concerning whether the iliac vein compression is a causative lesion resulting in leg swelling, chronic abdominal or pelvic pain, or other related symptoms. Venous stenting is considered but should not be performed without a clear indication that this procedure will result in a correction of the patient’s symptoms. Understanding the correlation between symptomatology and imaging findings is required to understand who may benefit from intervention. CT and magnetic resonance imaging do not provide hemodynamic information that is useful to determine whether venous narrowing is sufficient to cause significant symptoms, leading to continued debate over the degree of compression that is normal vs pathologic.

Defining the normal anatomy of the pelvic veins as seen on axial imaging would assist in determining when iliac vein narrowing on these images is pathologic. Cheng et al reported mean LCIV compression of 16% in 500 asymptomatic patients with a mean age of 55 years.¹² LCIV compression >50% was identified in only 10% of patients. In a study of 1600 asymptomatic patients with a mean age of 39.3 years, Li et al reported a mean compression of 46.2%.¹³ In this younger population, 47% of patients were found to have LCIV compression >50%.

There is a paucity of information in the literature related to the normal anatomy of the pelvic veins on axial imaging in patients under the age of 21 years. Li et al reported that younger patient age was a significant predictor of higher LCIV compression. However, they reported that patients aged 25 to 35 years had a higher mean compression than those aged 18 to 25 years.¹³ It is not clear how many patients were studied in the entire population under the age of 25 years, but this age group comprised only 6.4% of the 901 females in the study. Cheng et al reported a significantly higher degree of LCIV compression in the subset of patients aged <40 years in their study, particularly in females. Neither of these studies included patients under 18 years of age. Several studies identified a high incidence of compression of the LCIV in pediatric and adolescent patients who present with iliofemoral DVT but also found that these patients had a high incidence of other risk factors for DVT including hypercoagulable states and use of oral contraceptives.^14,15 Determining the relative contribution of iliac vein compression to the occurrence of DVT is difficult, particularly if the prevalence of iliac vein compression of varying degrees in the population of concern is unknown.

In this study, we found that the majority of patients aged 13 to 20 years undergoing CT imaging in the supine position had ≥70% stenosis of the LCIV as it moved under the right iliac artery and over the spine. This suggests that LCIV diameter reduction seen on axial imaging due to compression is the normal anatomy in this age group and that this finding should not be considered pathologic. It appears that as humans age, there is a change in the anatomy of the pelvic vessels, and compression of the LCIV becomes less severe over time. As we age, significant lengthening of the aorta has been reported to occur.¹⁶ This may result in movement of the distal aorta and iliac arteries more anterior to the spine, providing less compression on the LCIV. It is also possible that the pelvic veins change with aging. Elongation of the veins might result in less compression as the vein moves over the spine. The data from this study is not able to assess this possibility. Further work is needed to clarify the timing of these anatomic changes.

Previous studies have suggested that LCIV compression is more common in females.^12,17 Li et al reported that females accounted for 72% of cases with severe iliac vein compression in their study population.¹² In our study, females were found to have a significantly higher degree of compression in the older group, but in patients aged 13 to 20 years, there was no significant gender difference in LCIV compression. This may be related to female pelvic bone anatomy in some age groups, with variations in the curvature leading to a higher rate of compression. Although no differences in LCIV compression were found in both age groups based on race or ethnicity, this study has limited power to evaluate the effect of these factors sufficiently. BMI has also been reported to be associated with iliac vein compression.¹² Although we found that the BMI was significantly higher in older than younger patients, interestingly, there was no association between BMI and LCIV compression in either age group, indicating that retroperitoneal fat was not a protective factor against CIV compression. In examining numerous CT scans for our study, it appears that there is a significant variation in the course of the iliac artery across the spine that increases in older patients. In young patients, the artery is straighter, with less deviation anterior to the spine as it crosses. In older patients, there is a characteristic anterior movement of the RCIV as it crosses the spine, which may be a key factor in the difference in compression between the age groups. We plan to quantify these observations in future studies.

The study findings suggest that narrowing of the LCIV seen on CT imaging should not be a cause for clinical concern for pediatric patients and adolescents with no symptoms related to iliac compression. In young patients with left leg pain, swelling, pelvic pain, or similar symptoms, the finding of LCIV compression on axial imaging should be interpreted with the understanding that this may represent normal anatomy and not a pathologic finding.

The relationship of LCIV compression to DVT is complex, given that multiple possible risk factors for DVT are typically present in patients developing proximal DVT. Several authors have reported that severe compression of the LCIV is associated with a higher incidence of DVT.^4,18 Narayan et al reported a retrospective review of patients with acute DVT who had undergone CT imaging prior to the DVT event and related iliac vein compression to the incidence of DVT.⁴ They reported that LCIV compression <70% was not associated with an increased risk of DVT, but compression >70% was associated with increased odds of DVT. The mean patient age in this study was 57.5 years, so the relevance of this information to young patients is questionable. The reported incidence of proximal DVT in pediatric patients and adolescents is very low.¹⁹ If LCIV compression is very common in this population, the low incidence of DVT in patients with severe LCIV compression would question its strength as a risk factor for DVT in those under 21 years. Key guidelines documents related to the treatment of iliac vein disease have noted that additional research studying the impact of nonthrombotic iliac compression on at-risk populations is necessary to improve practice guidelines.²⁰

This study has several limitations. The data is obtained in patients undergoing CT imaging in the supine position who have abdominal pain and other conditions that might lead to dehydration or other factors affecting pelvic vascular anatomy. The findings may not be relevant to data obtained in other positions or after rehydration. However, the position and hydration status of the younger and older groups were likely similar, so the significant changes seen between the groups do not appear to be related to these factors. A second question concerns use of the more distal LCIV as the reference vessel for comparison to the compressed segment of the iliac vein. Another option would be to use the RCIV to eliminate the possibility that the LCIV is abnormally dilated due to more proximal stenosis. However, our evaluation of the LCIV compared with RCIV diameters did not identify any significant difference in young patients, with the RCIV being slightly larger. We did find that older patients had significantly larger right and left iliac vein diameters than younger patients, but the difference was markedly less than the difference in the compressed LCIV diameter between the age groups.

The correlation of CT AP imaging to intraluminal imaging with venography or intravascular ultrasound (IVUS) could be questioned; however, prior studies have indicated that CT venography (CTV) is a powerful screening method for venous obstruction. In a study comparing CTV with IVUS for the evaluation of nonthrombotic iliac vein lesions, CTV had a sensitivity of 93.1% and specificity of 77.5%.²¹ When combined with the evaluation of post-thrombotic iliac vein lesions, the positive predictive value was 94%, the negative predictive value was 79.1%, and the overall accuracy was 86.7%, demonstrating CTV is a good screening study. In another study, CTV showed excellent agreement with IVUS for both mild (<50% stenosis) and more severe stenosis (>50%) with sensitivities and specificities of 96% and 95% vs 100% and 100% respectively.²²

Another limitation of this study is the variability in indications of CT imaging for younger compared with older patients. Although the majority of patients in each group were studied for abdominal/pelvic pain, the other indications varied between the groups. Although we believe that the effect of the indications for the study would likely be limited, it would be interesting to perform prospective comparison of patients undergoing CT imaging for nonvenous indications to match the study indications and using a controlled hydration protocol. Also, additional studies in larger groups of patients will further define the normal pelvic vascular anatomy, its evolution as we age, and the variability of this based on gender and other patient characteristics.

Conclusions

In this study of patients aged 13 to 20 years undergoing CT imaging for unrelated symptoms, LCIV stenosis due to compression was identified in a majority of young patients. Compression was significantly greater in the young cohort than in older patients. More than one-half of young patients had ≥70% LCIV stenosis, suggesting that this is not a pathologic finding in this age group on CT imaging. The finding that this is a common anatomy in this patient group should be considered in treatment of patients with symptoms that might be related to LCIV compression.

Author Contributions

Conception and design: KW, NK, GS, WM

Analysis and interpretation: KW, LS, AB, NK, GS, SB, WM

Data collection: KW, LS, AB, NK, WM

Writing the article: KW, LS, NK, SB, WM

Critical revision of the article: KW, LS, AB, NK, GS, SB, WM

Final approval of the article: KW, LS, AB, NK, GS, SB, WM

Statistical analysis: SB, WM

Obtained funding: Not applicable

Overall responsibility: WM

Funding

None.

Disclosures

W.A.M. has been paid consulting fees by W.L. Gore. N.A.K. has been paid consulting fees by Medtronic. G.S. has been paid consulting fees by Medtronic, BD, Boston Scientific, Cook, Penumbra, and Philips.

From the American Venous Forum