An unusual variant of May-Thurner syndrome leading to deep venous thrombosis: a case report.

A 77-year-old female with past medical history of type 2 diabetes mellitus, hypertension, and chronic obstructive pulmonary disease (COPD) presented to the emergency department with left lower extremity (LLE) swelling, extending from the ankle to the hip, and pain for two days. She denied recent surgeries, trauma to the leg, prolonged travel, hormonal therapy, and immobilization. She denied any personal or family history of cancer or DVT. She also denied fever, chest pain, shortness of breath, and numbness or tingling of the left lower extremity. The patient had no history of smoking and denied any prior miscarriages. On examination, blood pressure 127/74 mmHg, heart rate 92/minute, respiratory rate 17, temperature 98.7 ℉; O 2 saturation 95%; cardiac and respiratory exams were normal. Noted was severe swelling of the LLE extending from the left foot to the hip region with mild tenderness on palpation associated with dusky discoloration with cyanosis at the toes; LLE was warm with 2+ dorsalis pedis pulses. There was no phlegmasia noted on the physical exam, and capillary refill time was less than two seconds. There was no sensory or motor deficit in the left lower extremity. Labs were significant for white blood cell (WBC) count 15.4×10 3 /µL, hemoglobin 14.2 g/dL, platelet count 309×10 3 /µL, D dimer 10.46 mg/L, creatinine 1.8 mg/dL, and HbA1c 7.0%. Duplex ultrasound revealed extensive LLE DVT extending from the external iliac vein (EIV) to the peroneal vein. A subsequent CT venogram demonstrated extensive DVT involving the LCIV, EIV, common femoral vein, popliteal vein, posterior tibial vein, and peroneal vein with small non-occlusive clot extending into the distal IVC with compression of the LCIV between the LCIA and vertebra, known as MTS ( Figure 1 ). CT venogram of left lower extremity showing compression of left CIV by left CIA (left CIV marked in red arrows). (A) Axial view. (B) Axial view thin cut CT image. CIA, common iliac artery; CIV, common iliac vein; CT, computed tomography. Patient was started on full dose anticoagulation with heparin infusion. Patient was taken to the interventional radiology suite, and the left popliteal fossa was prepped and draped. Using ultrasound guidance, the left popliteal vein was accessed with a micro puncture needle and a micro puncture sheath was advanced inside the vein. LLE venogram was performed which showed occlusive thrombosis involving femoral vein, common femoral vein, left EIV, LCIV and the distal inferior venacava (IVC) ( Figure 2 ). There was some non-occlusive thrombosis of the proximal IVC just above the bifurcation towards the left side. It was noted during percutaneous venogram that crossing the LCIV was difficult due to compression of the vein by the LCIA. An intravascular ultrasound (IVUS) was not available hence not used in the procedure. Venogram showing absence of flow in the left CIV due to DVT. CIV, common iliac vein; DVT, deep vein thrombosis. After fully anticoagulating the patient, a 16 French sheath was advanced inside popliteal vein and through that penumbra, a CAT 16 lightning device was advanced and thrombectomy was initiated. Significant thrombi were removed from the femoral vein, common femoral vein, left EIV, LCIV and the distal IVC. More chronic thrombi were removed from the LCIV and distal EIV during mechanical thrombectomy, indicating chronic compression suggestive of MTS. After sizing the caliber of the vein based on the CT venogram, a 14 mm × 90 mm Wallstent (Boston Scientific Technology Center, Minneapolis, MN, USA) was deployed across the entire common iliac vein and external iliac vein and postdilated with a 12 mm balloon. Repeat venogram showed excellent flow through the stented veins without evidence of remaining stenosis ( Figure 3A-3C ). The sheath was removed and the entry site in the left popliteal fossa was closed with good hemostasis. Patient tolerated the procedure well without any adverse events. Post operatively, she reported improvement in pain and LLE swelling; she was discharged home on apixaban and clopidogrel for a duration of 6 months. At 6-month follow-up, apixaban was discontinued, and patient was maintained on clopidogrel thereafter. A follow up LLE duplex ultrasound showed complete resolution of the DVT with normal flow in the veins up to the external iliac vein. Venogram showing left CIV (yellow arrows). (A) After mechanical thrombectomy. (B) With endovascular stent in situ . (C) Angiographically good flow post-stent placement. CIV, common iliac vein. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

May-Thurner syndrome (MTS), also known as Cockett’s syndrome, or iliac vein compression syndrome, is a congenital anatomic variant caused by extrinsic compression of the left common iliac vein (LCIV) between the right common iliac artery (RCIA) and the lumbar vertebrae ( 1 ). It was first proposed by Rudolf Virchow in 1851 that the increased incidence of venous thrombosis on left lower extremity was due to compression by the RCIA ( 2 ). MTS was first anatomically described by May and Thurner who demonstrated this anatomic variation as ‘spur like projection’ within the LCIV in 22% of the 430 cadavers they studied in 1957 ( 3 ). MTS occurs due to endothelial damage, intimal hyperplasia with collagen and elastin deposition, scarring, and formation of web or synechiae intravascularly in the left common iliac vein due to chronic pulsatile compression by the RCIA. This leads to partial or complete venous obstruction, which in turn predisposes to deep vein thrombosis (DVT) ( 4 , 5 ). The overall incidence of MTS is estimated to be 18–49%, whereas the true incidence of MTS is unknown as most individuals with this type of venous compression are asymptomatic ( 4 - 7 ). MTS is implicated in 2–5% of all patients who undergo evaluation for lower extremity venous disorders ( 8 ). MTS is usually left-sided and more prevalent in women in the 3 rd to 5 th decade of life with a ratio of 2:1 ( 9 ). Non thrombotic iliac vein lesion (NIVL) is defined as stenosis of iliac vein lumen due to extrinsic compression without associated thrombosis as seen in MTS. The clinical presentation of patients with NIVL range from being asymptomatic to demonstrating symptoms of chronic venous insufficiency such as lower extremity edema, varicose veins, venous claudication, venous ulcers, or symptoms of pelvic venous insufficiency such as chronic pelvic pain and dyspareunia in females. DVT and phlegmasia cerulea dolens (PCD) are complications of NIVL. PCD is a life-threatening condition associated with severe lower extremity pain, edema and skin mottling which occurs due to collapse of the arterial system in massive DVT leading to venous gangrene, sepsis and multiorgan failure ( 9 , 10 ). The risk factors for DVT in MTS include recent surgery, prolonged immobility, hypercoagulable disorders, immobilization, trauma, malignancy, pregnancy, postpartum, use of oral contraceptives, recent surgery, cumulative radiation exposure, and scoliosis. MTS comes into attention when it presents as DVT or pulmonary embolism ( 11 ). Various types of May-Thurner variants (MTV) have been sporadically documented in case reports. We present a rare case of variant MTS in an elderly female caused by compression of left common iliac vein by the left common iliac artery instead of the RCIA which led to DVT. This case report highlights the importance of being aware of the atypical cases or variants of MTS as a cause of left lower extremity DVT. We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-67/rc ).

MTS is more common than is expected; studies report that more than 50% luminal compression of the LCIA is seen in up to 25% of asymptomatic healthy individuals and that about 70% of patients with MTS are asymptomatic ( 4 , 12 ). MTS is diagnosed using duplex ultrasound, CT venogram, magnetic resonance (MR) venogram, conventional venogram, and intravenous ultrasound (IVUS) ( 13 , 14 ). Duplex ultrasound is usually the initial investigation that helps to diagnose DVT in a patient with lower extremity swelling. CT and MR venogram has high sensitivity in diagnosing MTS and helps ruling out other sources of extrinsic compression such as a tumor, hematoma, or lymph node and helps in identifying collateral vessels and visualizing deep veins in the pelvis which are technically difficult to be identified using duplex ultrasound ( 7 , 15 ). IVUS is the gold standard investigation as it may help visualize areas of stenosis and demonstrates intimal vascular changes such a webs, fibrosis, spur or mural wall thickening and permits accurate stent placement ( 7 , 16 ). Treatment of MTS include using compression stockings to improve symptoms of chronic venous insufficiency ( 10 ). Treatment such as anticoagulation and/or thrombectomy alone was found to have high rates of re-thrombosis; hence, endovascular treatment of intraluminal stenosis with catheter-directed thrombolysis or mechanical thrombectomy followed by stenting at the site of venous compression is preferred ( 17 ). Catheter-directed thrombolysis using tissue plasminogen activators (tPA) ensures higher local concentration of the thrombolytic agents and enables clot dissolution ( 9 ). Surgical options include RCIA dissection followed by venotomy, thrombectomy, excision of intimal spurs and vein patch angioplasty ( 8 ). Endovascular treatment has emerged as an effective alternative to open surgery in the treatment of MTS ( 18 ). Invasive venography for angioplasty can be done through femoral or popliteal access and a pressure gradient of more than 2 mmHg at the area of stenosis is of hemodynamic significance ( 4 , 7 ). The difficulty in crossing the LCIV in our case demonstrates focal constriction caused by intravascular changes owing to chronic pulsatile compression. The fact that more chronic thrombi were obtained from the LCIV and EIV also reflects chronic extrinsic compression of the LCIV. In our case, mechanical thrombectomy was performed for reduction of clot burden, followed by endovascular stenting. Re-establishment of vascular flow was then confirmed with repeat venogram. Advantages of endoluminal stenting include alleviation of pain and swelling of the lower extremity, preservation of valve function, and prevention of post-phlebitic syndrome ( 19 ). In events of single acute DVT occurrence due to MTS, anticoagulation with direct oral anticoagulants (DOACs) such as dabigatran, rivaroxaban, apixaban or edoxaban is preferred for a duration of six-to-twelve months after stent placement ( 20 ). Lifelong anticoagulation is suggested in the event of multiple occurrences of DVT ( 21 ). Duplex ultrasound can be used to assess stent patency in follow-up visit at 6 months. Complete symptom remission with stent placement and 100% primary stent patency rate in MTS patients were reported during an average follow up of three years ( 22 ). Our case report highlights the various anatomic variants of MTS. Whereas a majority of studies describes compression of the LCIV by the RCIA, our case describes an unusual case of compression of LCIV by the LCIA. Similar to our case, Hassell et al. have described a case of chronic left lower extremity swelling and venous stasis ulcer due to compression of the LCIV by a tortuous LCIA ( 23 ). However, our patient presented with DVT instead of venous stasis ulcer and the LCIA was not described as tortuous. A case report from Japan has also reported compression of LCIV by a tortuous LCIA leading to left lower extremity swelling ( 24 ). Our report is unique in that it is the first reported case of left lower extremity DVT due to the unusual variant of MTS causing compression of the LCIV by the LCIA. A few studies have reported compression of LCIV by the left internal iliac artery ( 25 , 26 ). Sharafi et al. have described compression of the LCIV by the left internal iliac artery near the confluence of the external iliac vein at a location different from the classic site of MTS compression ( 26 ). Burke et al. have reported right-sided MTS with compression of the right common iliac vein (RCIV) in a patient with a left-sided inferior vena cava (IVC) ( 13 ). Right-sided MTS due to situs inversus was reported by Im et al. wherein the RCIV was compressed between the LCIA and bony spur from fifth lumbar vertebra ( 15 ). The above patient also had a distended urinary bladder compressing the right external iliac vein due to sequelae of a stroke, leading to identification of the previously asymptomatic MTS ( 15 ). Arrazola et al. described a case of chronic extrinsic compression of the LCIV by the RCIA and acute compression of the proximal left EIV by a pelvic hematoma following renal transplant who developed early compartment like syndrome in the left lower extremity and worsening renal function due to ligation of the left internal iliac vein which was one of the main collaterals in chronic MTS ( 19 ). Pandit et al. reported MTS occurrence as a complication of endoluminal left internal iliac artery aneurysm repair with compression of the LCIV by the LCIA stent graft ( 14 ). There are a few reports of compression of the RCIV by the RCIA ( 6 , 10 , 27 ) and compression of the RCIV between the right internal and external iliac arteries ( 28 ). Fretz et al. have reported IVC compression by the RCIA due to a high aortic bifurcation ( 29 ). Other unusual presentations of iliac vein compression include compression by ectopic kidney, endometriosis, distended bladder due to prostate enlargement, and lumbosacral exostosis ( 30 - 35 ). Our report highlights the importance of considering the different anatomic variants that can cause MTS. In addition, this case emphasizes the importance of considering MTS as a cause of extensive left lower extremity DVT so that prompt treatment with catheter-directed thrombolysis with tissue plasminogen activator or mechanical thrombectomy and endoluminal stent placement in the obstructed left common iliac vein in addition to full dose anticoagulation can be instituted. This would prevent DVT re-occurrence and ensures alleviation of lower extremity symptoms. Vigilance of different anatomical MTV is essential for correct diagnosis and treatment. It also calls for endovascular treatment to be tailored depending on lesion anatomy. In our patient, IVUS could not be employed to better assess lesion anatomy from an intravascular perspective; however, this was supplanted by other investigative modalities, namely CT and percutaneous venograms. It is unknown the impact of different anatomic variants of MTS on treatment and prognosis. Even though all MTS variants as reported above, including our case, had resolution with endoluminal stenting, our report calls for enactment of formal guidelines that could dictate management of the different MTS variants.

A high index of suspicion is necessary to detect the underreported diagnosis of MTS, especially in females presenting with left lower extremity DVT. Physicians should also be aware of the different MTS variants when dictating management of such patients presenting as DVT, as treatment should always be directed towards rectifying the specific anatomical abnormality. Our report clarifies how to address the anatomical variant of MTS.

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