May Thurner syndrome: description of a case with unusual clinical onset.

May–Thurner syndrome (MTS) is a congenital vascular alteration that is part of a restricted category of very rare vascular syndromes that have in common the compression of an arterial or venous vessel. MTS, first described in 1957, is due to compression of the left common iliac vein against the lumbar spine by the adjacent common iliac artery. It can cause chronic thrombosis of the left lower limb and can give edema, pain, claudication, thrombophlebitis, and, in severe cases, pulmonary embolism. Color Doppler and duplex Doppler ultrasound allow us to easily locate the deep vein thrombosis, to measure its extension, and to highlight the vascular changes typical of MTS: compression and consequent hypertension of the left common iliac vein. The therapy depends on the degree of venous stasis and on the presence of venous thrombosis; generally, it consists of the administration of short- or long-term anticoagulant and thrombolytic drugs. In cases of severe stenosis of the left common iliac vein, the first-choice treatment consists of positioning a vascular stent, which resolves compression and significantly reduces chronic thrombotic episodes. We describe a case of MTS with an unusual clinical onset with pulmonary embolism.

May thurner sindrome, Iliac compression syndrome, Pulmonary embolism, Color Doppler

May–Thurner syndrome (MTS) is a vascular alteration that is part of a restricted category of very rare vascular compression syndromes, the best known of which are Nutcracker [1], Thoracic outlet syndrome [2], and Dunbar syndrome [3]. These syndromes are caused by the compression of an arterial or venous vessel, with characteristic clinical signs. MTS, first described in 1957 [4], is a rare congenital vascular alteration, in which the common left iliac vein is compressed against the lumbar spine by the contiguous iliac artery, resulting in venous hypertension and/or chronic thrombosis. According to the authors, two factors that predispose to chronic thrombosis are recognized: the reduction in the caliber of the common iliac vein and the chronic pulsations of the contiguous common iliac artery, which cause the formation of a “spur” in the venous wall. The stasis of the left common iliac vein causes, in most cases, edema and pain in the left lower limb, thrombophlebitis, claudication, etc., and, in the most serious cases, pulmonary embolism. In 84% of cases, compression of the left common iliac vein is caused by the right common iliac artery and rarely by the left common iliac artery [5]. In some cases, the compression of the left common iliac vein was caused by the bladder [6], aneurysms of the iliac artery [7, 8], endometriosis [9], a prosthesis of the penis [10], etc. Compression of the left common iliac vein can be symptomatic or asymptomatic [11]; moreover, it can be mild or hemodynamically significant. In a prospective study in asymptomatic patients, compression values greater than 25% are reported in 66% of patients with MTS, while values greater than 50% are reported in 24% of patients [12]. Compression can be considered hemodynamically significant when it exceeds 70% of the maximum vein size. Color Doppler, power Doppler, and duplex Doppler ultrasound can identify deep venous thromboses, measure their extension, and highlight alterations in the flow, providing a measure of the degree of the stenosis and hypertension [13]. Computed tomography (CT) is necessary for the diagnosis of pulmonary embolism and can highlight the vascular changes typical of MTS, allowing a differential diagnosis with other causes of compression of the left common iliac vein.[14]. The therapy of patients with MTS and deep vein thrombosis generally consists of the administration of short- or long-term anticoagulant and thrombolytic drugs. In the case of severe stenosis of the left common iliac vein, the most effective treatment is to place a vascular stent in the left common iliac vein, which resolves compression and significantly reduces chronic thrombotic episodes [15, 16]. Case report A 65-year-old woman was sent to our observation on suspicion of pulmonary embolism due to the appearance of dyspnea and alterations in laboratory indices (progressive increase in d-dimer). The patient had no lower limb symptoms or a history of venous thrombosis, phlebitis, or other vascular diseases. The patient underwent an angio-CT examination of the chest and angio-CT of the lower limbs. A CT multi-detector (Optima 64 slice, GE Healthcare) was used. Coronal, sagittal, and axial planar reconstructions of the iliac arteries and veins were performed. The minor and major calibers of the common iliac veins and the distance between the right common iliac artery and the adjacent spine were measured. The patient was also subjected to color, power, and duplex Doppler examination of the deep venous vessels of the lower limbs with an Aplio XG (Toshiba) device, with a 3.5-MHz convex probe and a 7.5-MHz linear probe. Longitudinal and transverse scans of the venous and arterial vessels were performed with the patient in supine decubitus position. The following were measured: the maximum and minimum diameters of the common iliac veins, their flow, and the flow ratio between the post-stenotic and pre-stenotic tracts. CT angiography of the chest revealed the presence of thrombosis of the right and left pulmonary arteries. CT examination of the lower limbs revealed a stenosis of the left common iliac vein with dilation of the pre-stenotic tract (diameter 21.2 mm) compared to the maximum diameter of the right common iliac vein (diameter 12.3 mm) (Fig. 1a–d). The aforementioned stenosis was caused by the right common iliac artery, which compressed the left common iliac vein against the L4 soma. The distance measured between the right common iliac artery and the vertebral column, at the level of the stenotic tract, was approximately 4.2 mm. In the pre-stenotic tract of the left common iliac vein, there was a thrombus (Fig. 2a–d). The color and power Doppler examinations showed no alterations in the caliber or flow of the right iliac vein, which had a maximum diameter of 12.3 mm and a minimum diameter of 9 mm; the duplex Doppler examination showed a peak speed of 18.7 cm/s. The left common iliac vein had a compression at the intersection with the right common iliac artery and a maximum and minimum diameter of 21.2 and 10 mm, respectively, in the pre-stenotic tract; the peak velocity was 7.3 cm/s in the pre-stenotic tract and 18 cm/s in the post-stenotic tract (Fig. 3a–d). The flow ratio between the post-stenotic and pre-stenotic tracts was 2.46 (18/7.3). No changes were found in the common iliac arteries. The patient was subsequently subjected to thrombolytic and anticoagulant therapy. The patient signed the informed consent form.

In symptomatic MTS, prolonged stasis generally causes the typical chronic manifestations of venous hypertension: swelling of the limbs, pain, claudication, thrombophlebitis, etc. Rarely, as in this case, does the onset of MTS occur with pulmonary embolism without other clinical symptoms. In our case, the thrombus did not completely obstruct the lumen of the vessel, and the stenosis was not of a high degree (< 70%; peak velocity ratio 2.46). For this reason, probably, they had not caused symptoms in the lower left limb; therefore, only one drug treatment was performed. According to some authors, compression of the left common iliac vein is a frequent alteration in asymptomatic cases and does not always present a risk [17]. Another peculiarity of this case is that in most MTS cases, the compression of the left common iliac vein almost always occurs against the fifth lumbar vertebra [18], while in this case the compression was against the fourth lumbar vertebra. CT angiography, necessary for the diagnosis of pulmonary embolism, has excluded other causes of venous compression, such as abdominal and pelvic masses, aneurysms, etc., and confirmed the stenosis of the left common iliac vein. CT examination, in accordance with the ultrasound examination, showed thrombosis, stenosis, and venous hypertension in the left common iliac vein. Duplex Doppler ultrasound measured the degree of stenosis, showing only a slight reduction in flow compared to the common contralateral iliac vein, a result that was valuable for the subsequent therapeutic setting. The therapy of patients with MTS must be proportionate to the severity of the stenosis: In asymptomatic patients with non-hemodynamically significant stenosis, it is possible to choose a conservative approach with short- or long-term thrombolytic and anticoagulant therapy. Therefore, thrombolytic and anticoagulant therapy with vascular stenting currently seems to represent the first-choice treatment for symptomatic MTS and in cases with hemodynamically significant stenosis of the left common iliac vein. According to the authors, in cases of upper limb thrombosis and edema, the endovascular treatment is successful in 91% of patients [19]. In addition, endovascular techniques, for some years, have replaced surgical thrombectomy and is the best approach when thrombolytic therapy is contraindicated.

This case confirms the importance of ultrasound examination in the diagnosis and therapeutic setting of MTS. In cases with pulmonary embolism, in the absence of other symptoms, we recommend, based on our results, a thorough study of the left common iliac vein to ascertain or exclude MTS. Author contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by RF, PVF, FAI, AC, IP, LF, SS and AB. The first draft of the manuscript was written by RF and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest. Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Statement related to the patient’s consent Consent was obtained from the patient for the publication of this case report and accompanying images. Footnotes Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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