Management of a Common Iliac Artery Aneurysm Causing Contralateral Iliac Venous Thrombosis

A 73-year-old male patient was diagnosed with thrombotic obstruction of the left common iliac vein (LCIV). Computed tomography imaging revealed a known -under follow-upisolated aneurysm of the right common iliac artery that seemed to directly obstruct the LCIV. Given the patient’s renal insufficiency as well as the size and anatomy of the aneurysm, the patient underwent open repair. The decision between open and endovascular repair, given the proximal DVT, is a dilemma, considering the risk for pulmonary embolism perioperatively as well as the venous thrombosis outcome postoperatively. Therefore, we present such an unusual case and discuss proper management.


Introduction
Aneurysms of the common iliac artery are rare, consisting less than 2% of all aneurysms [1]. Rarely, iliac artery aneurysms of significant size can obstruct venous outflow, manifesting as deep venous thrombosis (DVT). In these cases, DVT usually involves the ipsilateral, to the iliac artery aneurysm, iliac vein [2][3][4][5]. To our knowledge, there has been no case report to date referring to an isolated unilateral iliac artery aneurysm causing contralateral deep venous thrombosis due to iliac vein compression. Our aim is to present such an unusual case and make useful conclusions regarding proper management.

Case Report
A 73-year-old male patient presented in the emergency department complaining of pain and oedema in his left lower extremity for the last three days. His medical history revealed coronary artery disease under treatment, a recent percutaneous coronary angioplasty and renal insufficiency (serum creatinine: 2.2 mg/dl, clearance: 29.61 ml/min). The patient reported a known right common iliac artery aneurysm as well, followed-up closely with computed tomography (CT) imaging every year, for the last two years, in another institution. The patient reported that he had refused aneurysm treatment.
The previous CT evaluations revealed a steady increase in maximum aneurysm diameter: 5.5 cm at the beginning, 5.8 cm after one year, and finally, 6.2 cm with a 2.8 cm true lumen diameter on patient's admission CT (Figure 1). Ultrasound examination, as well as CT imaging, confirmed his clinical picture by illustrating a thrombosis of the left common iliac vein (CIV). Coloured duplex ultrasonography revealed a complete left CIV thrombosis extending from the iliac vein bifurcation to the origin of the left CIV. No floating thrombus extending proximally into the inferior vena cava, and no thrombosis of the right iliac veins were observed either. According to CT 3D-reconstruction analysis, there was a direct pressure effect from Regarding the surgical technique, a specific meticulous approach to the aneurysm, infra-renal aorta and iliac arteries was performed: a) Dissection was limited to the anterolateral walls of the arteries, no umbilical tapes or vessel loops were used to encircle their posterior walls in order not to dissect or get in proximity of the iliac veins; b) The patient was placed in 10 degrees anti-Trendelembourg position during the aneurysm dissection; c) A positive peep pulmonary pressure was initiated by the anesthesiologist during aneurysm clamping.; d) Evacuation of the aneurysm thrombus was completed very smoothly by irrigation with heparinized saline and using the surgeon's hand, taking into consideration not to apply any pressure on the left CIV or smash any thrombus by hand.
The internal iliac artery orifice was found obstructed, and an aorto-femoral bypass was performed, using an 8 mm Dacron graft ( Figure 3). The proximal anastomosis was located almost 5 cm above the aortic bifurcation, and the distal anastomosis at the level of the common femoral artery bifurcation. Intraoperatively, the patient received intravenous unfractioned heparin as well. Surgical thrombectomy of the left CIV with an additional venous fistula was also an option. However, the patient had no strong indication for it (no leg phlegmasia) and the whole operative invasiveness would increase dramatically this way.
Finally, postoperative graft patency was optimal, with pulses palpated above the superficial and deep femoral arteries, and significant arterial blood flow peripherally confirmed by linear ultrasonography. Five months after surgery, patient's follow-up remains unremarkable. He has a complete iliac vein recanalization and he will discontinue fondaparinux in one month.

Discussion
Aneurysms of the common iliac arteries present therapeutic and surgical challenges [6]. In most cases, complex surgical techniques are required in order to restore proper vascular function [7]. In this case report, the aneurysm was of considerable size, significantly larger than the average sizes at which common iliac artery aneurysms are first diagnosed [8]. The delayed diagnosis could be easily explained as the diagnosis of isolated iliac artery aneurysm on physical examination is extremely difficult because of the deep pelvic location of these aneurysms and likely accounts for the high incidence of symptomatic or ruptured aneurysms in the past [9]. It is highly suggested that iliac artery aneurysms above 5 cm require prompt surgical repair since there is considerable risk of rupture [10,11]. The increasing size of the aneurysm and the absence of sufficient neck at the common iliac artery classified it as a suitable candidate for open surgical repair [1,8,12].
Although this aneurysm remained 3 years untreated with a considerable risk of rupture, it alternatively commenced applying pressure to contralateral structures leading to venous thrombosis. The expansion of this right iliac artery aneurysm from 5.5cm to 6.2cm should be considered as the main reason for left CIV thrombosis, and therefore DVT in this case might have been the result of non-optimal management. Furthermore, it would be interesting to correlate this case report with the well-known May-Thurner syndrome. May-Thurner is a relatively rare syndrome and is defined by the pressure phenomenon caused by the right iliac artery towards the left iliac vein [13][14][15]. However, this case cannot be classified as May-Thurner syndrome for two main reasons: (i) In the case of May-Thurner, there is constant pressure applied by the right iliac artery, causing long term effects, such as left lower limb oedema, pain and recurrent deep venous thrombosis. In our patient, the right iliac artery had presumably been dilated at least 3 years since the first diagnosis, concurring with the natural history of iliac artery aneurysms [8]. Moreover, the patient had remained asymptomatic with no other episode of deep venous thrombosis reported before, excluding the existence of May-Thurner syndrome [16,17]. (ii) May-Thurner syndrome excludes cases of right common iliac artery aneurysms, since pressure dynamics and nutcracker effect, which is the key-point for May-Thurner syndromeis greatly altered in these cases [18,19].
Regarding proper management, the current consensus is that elective repair should be considered in good risk patients for isolated iliac artery aneurysms greater than 3 to 4 cm in maximal transverse diameter [8,20]. However, there are no official guidelines supporting either open or endovascular technique. Although, endovascular repair of isolated common iliac artery aneurysms has proved to be safe and effective, especially for high-risk patients [21,22], the traditional preferable choice for treatment of common iliac artery aneurysms, in standard risk patients, is open interposition graft repair [20].  Especially for common iliac aneurysms with compressive symptoms, Huang et al conclude in a large retrospective study that open repair is preferred [8]. Possibly, aneurysm sac evacuation during open repair decreases aneurysm compression on the vein, and therefore, promotes rapid vein recanalization and prevents post-thrombotic syndrome.
Abdominal surgery in the presence of acute DVT remains a debatable issue. Perioperative management should be modified in order to prevent pulmonary embolism. Conventional treatment is often not an option in the perioperative period, as surgical bleeding may be equally life threatening as a pulmonary embolism [23]. However, our patient was fully anticoagulated before, during and post-surgery, with satisfying results. Additionally, it is common practice to insert an inferior vena cava filter in such cases of higher risk for DVT preoperatively [24], especially if one is planning to perform a vein thrombectomy. However, this could further complicate the procedure, given the unfavorable morphology of the vein thrombus as shown in ultrasonography. Finally, aneurysm resection was mandatory for the good outcome of the venous thrombosis in our case, given that special measures would have been taken during surgery. A non-traumatic surgical approach, proper positioning of patient and positive peep pressure during mechanical ventilation are imperative.
Furthermore, chronic pressure of a common iliac artery aneurysm on a venous structure could lead not only to venous thrombosis but to arterio-venous fistula (AVF) formation as well [25]. Open repair seems to offer the advantage of fistula control within the aneurysmal sac, avoiding pulmonary embolization of debris from the aneurysm sac, although successful repair of AVFs using endovascular repair has also been reported [25]. However, open repair seems to be associated with a higher incidence of early postoperative complications, including cardiac events, and the risk of pulmonary embolism [8].

Conclusions
Large isolated common iliac artery aneurysms should be promptly treated after initial diagnosis. Deep vein thrombosis is a possible but rare complication of extensively postponing a common iliac artery aneurysm repair. Open surgery under proper intraoperative anesthesia and non-traumatic dissections could have satisfying results, even when no cava filter insertion or venous thrombectomy are performed.