When Anatomy Meets Pathology: May-Thurner Syndrome as an Underdiagnosed Cause of Acute DVT

Abstract

May-Thurner Syndrome (MTS) is an underrecognized anatomic cause of left-sided deep vein thrombosis (DVT) resulting from compression of the left common iliac vein by the overlying right common iliac artery. Although it accounts for approximately 2-5% of DVT cases, it may be overlooked when other provoking risk factors are present, leading to incomplete treatment and risk of recurrence. We report a 61-year-old woman with no prior history of venous thromboembolism who presented with one week of progressive left lower extremity swelling and pain following recent femoral venous catheterization during a prior hospitalization. Imaging demonstrated extensive proximal iliofemoral DVT involving the left external iliac, common femoral, and superficial femoral veins. Despite initiation of intravenous anticoagulation, the significant clot burden prompted aspiration mechanical thrombectomy. Post-procedural venography revealed persistent residual stenosis of the left common iliac vein, raising suspicion for underlying iliac vein compression. The distribution of thrombosis and focal stenosis was consistent with MTS. Balloon venoplasty was unsuccessful, and definitive management was achieved with placement of a 16 mm × 80 mm venous stent, resulting in restoration of inline venous flow. The patient was transitioned to oral anticoagulation with dual antiplatelet therapy and experienced clinical improvement without complications. This case highlights MTS as an important and potentially underdiagnosed cause of extensive left-sided DVT, particularly when thrombus burden appears disproportionate to apparent provoking factors. Recognition of this anatomic variant is essential, as anticoagulation alone may be insufficient and endovascular intervention is often required to prevent recurrence and long-term venous morbidity.

Introduction

Deep vein thrombosis (DVT) of the lower extremity is a relatively common condition, with an incidence of roughly 1 in 2,000 people annually. ¹ Venous thromboembolism (VTE), encompassing both DVT and its potential sequelae pulmonary embolism (PE), carries a substantial risk of death, with estimated mortality rates of 10.6% and 23% at 30 days and 1 year, respectively. ² Risk factors for VTE are well described and include demographic factors such as age and sex, lifestyle factors such as smoking and obesity, genetic factors such as inherited thrombophilia and sickle cell disease, and acquired factors such as malignancy, major surgery, inflammatory disorders, and hormonal alterations. ¹ Many of these risk factors stem from the work of Virchow in the mid-19th century, who also described a left-sided predominance for DVT. Expanding on that foundation, May and Thurner identified an important anatomic risk factor for DVT and coined the term May-Thurner Syndrome (MTS) in the 20th century.^3,4

MTS classically occurs when there is compression of the left common iliac vein by the right common iliac artery anteriorly and the vertebral body posteriorly, leading to endothelial injury, venous stasis, and ultimately DVT.^3,4 It may also occur due to other forms of extrinsic compression of the iliac veins, including rare cases involving compression by adjacent structures such as the bladder or kidney.^5,6 Rare right-sided variants have also been described. ⁴

Long-term management of DVT and VTE, including duration of anticoagulation, depends on the estimated risk of recurrence and identification of precipitating factors. ¹ The acute phase of high-risk DVT is typically managed with anticoagulation for at least three months, with extended therapy reserved for those at higher recurrence risk. ¹ Catheter-based therapy has shown mixed results and is not routinely recommended for acute lower extremity DVT.^1,7 However, in patients with anatomic compression such as MTS, early endovascular intervention with balloon angioplasty and stenting, in addition to anticoagulation, may be necessary to prevent recurrent VTE.^8,9

Approximately 2-5% of DVT cases are attributed to MTS, ¹ making it a relatively uncommon but clinically significant predisposing factor for VTE. In conjunction with traditional risk factors, such anatomic variations require distinct diagnostic and therapeutic consideration. In this report, we emphasize the importance of recognizing MTS in patients presenting with proximal DVT.

Case Presentation

A 61-year-old Eastern European woman (from Russia) with a past medical history significant for anxiety and hypertension presented to the emergency department with one week of progressive swelling and pain of the left lower extremity. She reported that this had never occurred previously. She denied recent travel, prolonged immobility, recent surgery, active malignancy, weight loss, night sweats, chest pain, shortness of breath, abdominal pain, gastrointestinal bleeding, or urinary symptoms. She had a 15+ pack-year smoking history and denied alcohol or intravenous drug use. There was no family history of deep vein thrombosis (DVT) or pulmonary embolism (PE).

One week prior to presentation, she had been admitted to an outside institution for management of a panic attack. During that hospitalization, multiple attempts to obtain upper extremity intravenous (IV) access were unsuccessful, necessitating placement of a left femoral venous catheter. The femoral IV remained in place for approximately three to four days. Upon removal, significant bleeding occurred, requiring prolonged manual compression. Shortly thereafter, she was diagnosed with acute left lower extremity DVT and initiated on anticoagulation therapy. However, she left the hospital against medical advice because she did not wish to continue oral medication. She subsequently presented to our institution with persistent left leg swelling and pain.

On arrival, she was afebrile and hemodynamically stable with a temperature of 98.2°F, heart rate of 91 beats per minute, blood pressure of 112/63 mmHg, respiratory rate of 18 breaths per minute, and oxygen saturation of 95% on room air.

Physical examination revealed diffuse swelling of the left lower extremity extending to the upper thigh, with associated erythema, warmth, and tenderness to palpation. Pitting edema was present, and the left limb circumference was significantly greater than the contralateral extremity. Distal dorsalis pedis pulses were +2 bilaterally. The remainder of the examination, including cardiopulmonary and abdominal evaluation, was unremarkable.

Laboratory evaluation demonstrated hemoglobin of 9.6 g/dL (13.1-15.5 g/dL), white blood cell count of 5.8 ×10⁹/L (4.8-10.8), platelet count of 201 ×10⁹/L (130-400 ×10⁹/L), and creatinine of 1.2 mg/dL (0.7-1.3 mg/dL). Iron studies were consistent with iron deficiency anemia with serum iron 27 µg/dL (15-170 µg/dL), transferrin saturation 11% (20-50%), and ferritin 56 ng/mL (10-204 ng/mL). Reticulocyte count was 1.2% (1-2%), and lactate dehydrogenase and haptoglobin levels were within normal limits.

Chest radiograph revealed no acute pulmonary pathology.

A bedside venous ultrasound demonstrated DVT involving the left groin vein. Interventional Radiology was consulted and recommended further imaging to evaluate clot burden. A computed tomography (CT) venogram of the abdomen, pelvis, and left lower extremity demonstrated extensive proximal DVT involving the left superficial iliac vein, left external iliac vein, left common femoral vein, and proximal superficial femoral vein. Associated subcutaneous fat stranding and haziness of the lower left pelvis and visualized left leg were noted, consistent with edema or inflammation.

Given the extent of iliofemoral thrombosis, therapeutic anticoagulation was initiated with intravenous heparin infusion.

Due to the significant proximal clot burden and risk of complications, the patient underwent aspiration mechanical thrombectomy using the Inari FlowTriever16 curve system (“T16,” Inari Medical, Irvine, California). Post-thrombectomy venography demonstrated resolution of the thrombus but revealed persistent residual stenosis of the left common iliac vein (LCI) (Figure 1).

Figure 1.

Post-thrombectomy Venogram: Venography revealing persistent residual stenosis of the left common iliac vein (orange arrow) despite thrombus removal

The presence of persistent residual stenosis of the left common iliac vein following successful thrombectomy raised strong suspicion for an underlying anatomic compression. The location of the stenosis, in conjunction with extensive left-sided iliofemoral thrombosis, was consistent with MTS, in which the right common iliac artery compresses the left common iliac vein against the lumbar vertebral body (Figure 2). This anatomic variant results in chronic endothelial irritation and venous stasis, predisposing patients to left-sided proximal DVT. In this case, recent femoral venous catheterization likely served as an additional provoking factor superimposed on underlying iliac vein compression, culminating in extensive thrombus formation.

Figure 2.

Axial CT venogram demonstrating compression of the left common iliac vein between the right common iliac artery and vertebral body (blue arrow)

Balloon venoplasty was attempted; however, it was unsuccessful in adequately relieving the stenosis. Therefore, a 16 mm × 80 mm VenoVo venous stent (BD, Franklin Lakes, New Jersey) was deployed across the stenotic segment (Figure 3). Completion venography demonstrated restoration of inline venous flow without residual obstruction.

Figure 3.

Fluoroscopic image demonstrating deployment of a 16 mm × 80 mm venous stent with restoration of inline venous flow (black arrow)

The patient tolerated the procedure well without immediate complications.

Following intervention, she was maintained on continuous intravenous heparin infusion with serial PTT monitoring and subsequently transitioned to oral anticoagulation. Dual antiplatelet therapy with aspirin and clopidogrel was initiated in addition to anticoagulation.

Her hospital course was otherwise uncomplicated. She remained hemodynamically stable, and her left lower extremity swelling gradually improved without evidence of bleeding or procedural complications.

She was discharged home on oral anticoagulation and dual antiplatelet therapy with outpatient follow-up arranged with Interventional Radiology and Hematology.

Discussion

In this case of MTS, the patient presented with multiple risk factors for VTE, including recent endothelial injury and venous stasis. Oftentimes, such risk factors are adequate to provide a reasonable cause for DVT, and no further workup is performed. This likely contributes to the low reported prevalence of the syndrome, as pelvic imaging is not usually pursued in the presence of clear provoking agents.

Various diagnostic modalities can be used for the diagnosis of VTE in MTS. Contrast venography has been described as the diagnostic gold standard, ¹⁰ and the most commonly reported diagnostic modalities in practice include computed tomography venography, conventional venography, magnetic resonance imaging, and intravascular ultrasound (IVUS). ³ In the case described above, CT venography of the lower extremity was utilized, which has demonstrated 100% sensitivity and 100% specificity in diagnosing iliac vein obstruction in highly symptomatic patients with severe chronic venous disease and obstruction greater than 50%, with 96% sensitivity and 95% specificity when the degree of obstruction is less than 50%, outperforming both IVUS and duplex ultrasound. ¹¹

In this case, after CT venography demonstrated extensive DVT, thrombectomy was performed and resolution of the thrombus was confirmed by repeat venography. However, residual stenosis of the left common iliac vein was noted, which is consistent with the diagnosis of MTS and highlights the necessity for endovascular management. Reconstruction of the iliac vein with balloon angioplasty was the next step performed for this patient and is a safe and effective approach for managing MTS. ¹² Stent placement for patients with left common iliac vein compression results in clinical improvements such as symptom relief and resolution of obstruction in both patients with DVT and those with non-thrombosed iliac lesions. ¹³ Stent placement remains a cornerstone in the management of MTS, with patency rates of approximately 96% at 12 months following endovascular treatment. ³ Although anticoagulation alone is often adequate for VTE management, patients with MTS benefit from endovascular treatment, and consideration of this condition may be warranted in otherwise unexplained cases of recurrent lower extremity DVT.

This case emphasizes the importance of recognizing MTS, which is likely underreported and consequently under-recognized by providers. Although advancements in anticoagulation strategies have significantly improved the management of VTE, MTS represents a scenario in which anticoagulation alone may be insufficient, and additional endovascular intervention is required to reduce recurrence rates. As an underreported phenomenon, there is an opportunity for future studies to explore associations with other conditions, such as chronic thromboembolic pulmonary hypertension (CTEPH), which has been associated with the anatomic features of MTS, and may help identify patients that could benefit from thromboendarterectomy. ¹⁴ With increased awareness, diagnosis, and reporting, large prospective multicenter studies may better define additional associations, prognostic indicators, and optimal treatment strategies for MTS.

Conclusion

MTS is an underrecognized anatomic cause of lower extremity DVT, as iliac vein compression is unlikely to be considered in the standard evaluation of DVT with dedicated pelvic imaging. This case highlights the importance of maintaining clinical suspicion for MTS in patients with proximal or extensive left-sided DVT, especially when the thrombus burden appears disproportionate to the provoking risk factors. Several imaging modalities including venography can be used to make the diagnosis, while endovascular intervention with angioplasty and stenting addresses the underlying mechanical obstruction in order to reduce recurrence. Increased recognition of this condition may assist providers in the management of patients with recurrent DVT. On a population scale, increased reporting may lead to larger, multicenter prospective studies and assist in the reduction of morbidity associated with recurrent VTE.