May-Thurner syndrome: an unusual cause of unprovoked deep vein thrombosis of the left lower limb

Abstract

May-Thurner syndrome, an unprovoked form of deep vein thrombosis (DVT), should be kept in mind in case of DVT with no predisposing factors. We present a case of a 37-year-old male with DVT of left lower limb due to May-Thurner syndrome, treated with anticoagulants with a plan of left common iliac vein (LCIV) stenting and inferior vena cava (IVC) filter later. Venous duplex scan showed features suggestive of May-Thurner syndrome. Hence, we proceeded for CT abdominal aortogram with bilateral lower limb angiogram, which confirmed the above findings. Management of May-Thurner syndrome is a stepwise approach, with initial anticoagulation for dissolution of the thrombus followed by endovenous stenting of the LCIV and concomitant IVC filter.

Background

Deep vein thrombosis (DVT) is a common entity encountered in the medical fraternity, and the most common causes are pathophysiological. Overall, the treatment consists of prevention of risk factors and treatment of the thrombogenic phenomenon. However, there can be exceptions in the form of normal anatomical aberrations in the absence of any risk factors. An unfamiliar exception to this is May-Thurner syndrome (MTS), which is an anatomical aberration causing the right common iliac artery (RCIA) to compress the left common iliac vein (LCIV) as it passes over it. MTS commonly affects women with a mean age of 40 years; however, the exact incidence and prevalence are unknown because the anatomical features of this condition are not associated with specific symptoms until thrombosis occurs.¹ Patients commonly present with unilateral, unprovoked and recurrent DVT. We hereby present a case of anatomical variation in the blood vessels causing DVT known as MTS.

Case presentation

A 37-year-old male without any prior history of prolonged immobilisation, recent trauma or major surgery came with complaints of pain in the entire left lower limb from the hip to the foot, more in the thigh since the past 2 months, aggravated since the past 2 days, and associated with swelling of the calf. There was no associated history suggestive of an arterial cause or soft tissue infection. There was no history of diabetes mellitus, hypertension or dyslipidaemia. On examination, the left calf region showed swelling with tenderness but no local rise of temperature, skin changes or erythema.

Investigations

The patient was evaluated for causes of DVT using radiological modalities of the venous duplex scan, which showed compression of the LCIV with prestenotic dilatation, indicating external compression most likely due to RCIA suggestive of MTS. Hence, we proceeded for CT abdominal aortogram with a bilateral lower limb angiogram, which revealed compression of the LCIV by the iliac arteryRCIA with echogenic thrombus in LCIV (figure 1).

Figure 1.

Representative images of CT abdominal aortogram with a bilateral lower limb angiogram. (A) Sagittal view showing the left common iliac vein compressed by RCIA. (B) Axial view taken at the level of green line in figure A showing the compression. LCIA, left common iliac artery; RCIA, right common iliac artery; RCIV, right common iliac vein.

Differential diagnosis

Considering the age and absence of other signs of inflammation, unprovoked DVT of the the left lower limb was our main diagnosis. Initial venous Doppler of the left lower limb did not show any evidence of DVT. Second opinion was taken for venous Doppler and then, features of MTS were noted. With CT abdominal angiogram, the cause was confirmed.

Treatment

The patient was managed conservatively with anticoagulants during the acute episode with low-molecular-weight heparin and was given maintenance coagulation of dabigatran 150 mg two times a day, with a plan for LCIV stenting and inferior vena cava (IVC) filter thereafter.

Outcome and follow-up

Follow-up with venous Doppler after 1 month showed subacute thrombosis with echogenic filling of common femoral, superficial femoral, popliteal and one of the venae comitantes of posterior tibial vein. Cardiologist advised for continuation of anticoagulation, and deferred stenting to later date. The need for IVC filter was discussed with the patient. As he had financial constraints, he chose anticoagulation therapy and will come for IVC filter at a later date. He was on long-term anticoagulation with every 6 monthly radiological follow-up to confirm recanalisation, combined with prevention of further risk factors.

Discussion

DVT is a routine clinical entity encountered by surgeons, general physicians, gynaecologists and orthopaedicians as a part of various diagnostic and therapeutic conditions concerning their specialties. Multiple risk factors have been identified, such as prolonged immobilisation, oral contraceptives, pregnancy, trauma, postsurgery sequelae, tobacco consumption and hypercoagulable states. Once the diagnosis of DVT is made and a co-relation to the identifiable risk factor is established, all further efforts are confined to the management of DVT and elimination of the underlying cause.

MTS, first described in 1957, is a normal anatomical variation, where the RCIA compresses the LCIV. Although the incidence of MTS is inconstant, May and Thurner have promulgated that this variation is present in 22%–25% of the general population, identified in autopsy specimens. It is very unclear which among these patients are likely to develop DVT, and probably the degree of compression might have a role to play.^{2 3} Although Oguzkurt et al hypothesised in their study that at least 70% of compression of LCIV is needed to produce DVT, there is evidence of DVT in cases where compression is less than the mentioned cut-off. There is a diagnostic conundrum in these studies as a venogram is not routinely done to know the exact degree of compression.^{3 4} In the absence of any risk factors, compression of LCIV in MTS alone does not cause DVT until there is chronic intimal hyperplasia resulting in venous stasis and thrombosis or ‘spur’.^{4 5}Continuous external compression by the external iliac artery leads to vein wall hypertrophy, spur formation and intimal fibrosis, leading to a procoagulant state and thrombosis of the external iliac vein, and venous hypertension.⁶ The literature review reveals a correlation between thrombophilia and MTS. Kiernan et al⁷ found that among 30 patients with IVC syndrome, 12 patients had a positive thrombophilia work-up.⁸

This condition is more common in women than men aged 25–50 years, plausibly due to a wider female pelvis pushing the lower lumbar vertebrae forward and compressing the LCIV against the RCIA.³ Pelvic anatomical structures undergo series of changes in pregnancy. Thus, obese females can develop malalignment of vascular structures in the retroperitoneum during the postpartum period. This can potentially lead to MTS.

This normal anatomical variation or ‘anomaly from the patient’s perspective’ is not easily picked by ultrasound as it occurs high in the pelvis. Contrast venography/magnetic resonance venography and intravascular ultrasound are currently considered the best modalities for diagnosis that can precisely pinpoint the site and extent of thrombosis, but also identify the prestenotic dilation of LCIV due to compression of RCIA in MTS. CT-arteriogram can be an additional help to further substantiate the diagnosis.⁶

Management is a stepwise approach of initial anticoagulation for dissolution of the thrombus, followed by endovenous stenting of the LCIV and concomitant IVC filter. Observational studies of over 1400 such procedures (catheter-directed thrombolysis, venoplasty and/or stent placement) with a median follow-up of 16 months (range, 6–63 months) in the literature have found primary patency rates of 58%–96%, and symptom improvement/relief in 68%–83% of patients.⁹ The endovenous procedure has certain complication reported by Mahnken et al. The mortality rate is low after endovenous revascularisation ranging from 0% to 1%. Early (<30 days) recurrence of thrombosis occured with an incidence of 1.5%–3% compared with late rethrombosis of 5%. They mentioned that,

In about 1% of patients, extending the stent into the IVC causes iliac vein blockage on the contralateral side. In May-Thurner syndrome, however, failure to extend the stent in the IVC and so completely cover the underlying lesion results in a 36 percent ipsilateral restenosis or occlusion rate.

Venous tears, injury of an adjacent artery, stent fracture and stent dislocation were the rare complications.¹⁰

Regarding the anticoagulation following endovenous procedures, Padrnos et al in their study looked at risk factors linked with venous thromboembolism (VTE) recurrences and weighed the danger of future VTE against the risk of antithrombotic-related severe bleeding. Treatment with anticoagulation for a finite length of 6 months following stent installation (with or without additional antiplatelet therapy) is feasible in the context of major transitory risk factors such as surgery or oestrogen exposure. In the absence of a major temporary risk factor (other than a constricted left iliac vein), extending anticoagulation beyond 12 months is a difficult option. After 6–12 months of therapy, anticoagulation can be stopped, especially if there is little or no indication of venous insufficiency.¹¹

This case posed a challenge to the authors, as there was difficulty in the passage of stent due to thick intimal spur. Long-term anticoagulation with every 6 monthly radiological follow-up to confirm recanalisation, combined with prevention of further risk factors, is the best suitable strategy for such cases until definitive endovascular drug-eluting stents can be deployed and IVC filter inserted.^{5 6}

Patient’s perspective.

I had severe pain in the entire left lower limb for 2 months which was disturbing my work in the agricultural field. I had consulted various doctors. Finally, they said there is an obstruction in the blood vessel carrying blood to the heart. My innocence had made me to worry a lot, which subsided as the pain decreased on the initiation and maintenance of treatment.

It took almost more than a month of treatment for my symptoms to subside. After 4 months of treatment, I am back to my work and almost pain-free. I have been advised, the need for further procedures on follow-up.

Learning points.

• The authors have brought up this rare cause of common disease in the form of May-Thurner syndrome (MTS), which can cause unprovoked deep vein thrombosis.

• MTS was seen in a male in our case as it is traditionally thought to be present in females.

• Management is a stepwise approach of initial anticoagulation for dissolution of the thrombus followed by endovenous stenting.

• Hence, it is of paramount importance that such anatomical variants must also be kept as a part of our clinical judgement when encountering common clinical situations.

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