Pelvic kidney as a cause of May-Thurner syndrome

Introduction

Pulmonary embolism is the main reason for mortality and occurs in about one-third of cases of DVT, whereas the post-thrombotic syndrome is the main reason for morbidity in DVT. ¹ Post-thrombotic syndrome occurs in up to 50% of patients with DVT within the first two years and presents with a continuum of leg pain, swelling and venous ulceration. ¹ DVT, with its sequelae, is a common clinical problem which affects 1–2 per 1000 individuals per year. ² Venous thrombosis is the cause of 500,000 deaths annually in Europe and more than 300,000 in the United States; it was shown to be the leading cause of ‘disability-adjusted life years’ (DALYs) in low- and medium-income countries and the second leading cause in high-income countries. ² Interestingly, the incidence of both DVT and DVT recurrence is higher in men than in women. ³ Of importance is the fact that distal (below-knee) DVTs are usually the result of transient situations, while proximal DVTs are more strongly related to chronic conditions. ⁴

As new research constantly reveals new causes for DVT, they all can still be grouped into Virchow's triad, first published in 1856 ¹ : venous stasis, vascular injury and hypercoagulability.

Case report

A 52-year-old Caucasian man presented with a second episode of proximal DVT of his right leg. A comprehensive and systematic search for occult malignancy and other known biochemical causes of thrombophilia did not reveal any known cause. He had no known diseases, never had any surgery and was not taking any medication. He had never smoked and never took any illicit drugs.

The first episode of proximal DVT occurred six months after he started intensive cycling at the age of 50 years. The second, apparently unprovoked episode, also on the right, occurred two years later while he was still taking a daily dose of 15 mg rivaroxaban.

It should be noted that both episodes became clinically evident shortly after a competitive, long distance cycling event.

Figure 1 demonstrates a right-sided pelvic kidney (yellow arrow). Figure 2 on the left demonstrates a patent right common iliac vein (short white arrow). Figure 2 on the right demonstrates compression of the right common iliac vein during flexion of the right hip (long white arrow). There are also well-known anatomic causes of DVT and one such anatomic cause is the May-Thurner syndrome, also known as iliac vein compression syndrome. OPEN IN VIEWER

OPEN IN VIEWER

Figure 2.

Patent right common iliac vein (short white arrow). Compression of right common iliac vein during flexion of right hip (long white arrow).

In this particular patient, it is evident that during flexion of the right hip, as occurs repetitively during cycling, compression of the right iliac vein occurs by the pelvic kidney (Figure 2).

Rivaroxaban was discontinued and was replaced by coumadin (warfarin) and his international normalised ratio (INR) was maintained in the range of 2–2.5 with no recurrence of DVT for 48 months, despite regular bouts of intense cycling.

Discussion

In 1957, May and Thurner became the first to describe an anatomical variant where an overriding right common iliac artery compresses the left common iliac vein against the spine and in this way causes recurrent DVT on the left. ⁵ Also known as Cockett syndrome or iliac vein compression syndrome, this condition is also associated with other vascular anomalies, such as arteriovenous fistulas and Klippel-Trenaunay syndrome. ⁵ This anatomical variant described by May and Thurner is much more prevalent than previously thought, with some studies suggesting that this is associated with 37%–72% of all proximal iliofemoral DVTs.^6–8 Since the original report in 1957, several anatomical variants of May-Thurner syndrome have been published. ⁸ These include left common iliac vein compression by the left internal iliac artery, compression of the right common iliac vein by the right internal iliac artery, compression of the inferior vena cava by the right common iliac artery and even variants associated with a left-sided inferior vena cava. ⁸ Regardless of the specific anatomical variant, such chronic compression of the venous wall leads to a specific structural alteration, called venous spur formation. ⁸ Such ‘spurs’ consist of extensive local intimal proliferations with elastin and collagen accumulations. ⁸ These ‘spurs’ then lead to impaired venous return and in this way contribute to the formation of venous thrombosis. ⁸

Rare reports of pelvic kidneys as a cause of lower-limb DVT do exist. ⁹ However, the report by Vittore and Murray ⁹ is of importance, as they clearly demonstrated the potential transverse mobility of a pelvic kidney, which may lead to intermittent venous compression of either the left or right common iliac vein. This case report also clearly demonstrates intermittent compression of a common iliac vein, in this case the right, during flexion of the right hip, as occurs during cycling.

This case demonstrates the need for an anatomical imaging study of the pelvis in cases of recurrent proximal thrombosis of the lower limb. Furthermore, this case raises the clinical question of which is the most effective anticoagulant in cases of May-Thurner syndrome—coumadin which inhibits factor II, VII, IX and X or the newer oral anticoagulants which inhibits either factor II or V.