A Rare Case of Iliac Saccular Aneurysm Communicating with a Transplant Renal Artery

Introduction

Isolated iliac aneurysms (IAs) are defined as an iliac artery with focal dilation of at least 50% beyond the expected normal vessel diameter [1]. Unlike a pseudoaneurysm, which is actually a disruption of the arterial wall with a surrounding hematoma that compresses surrounding tissues, an IA is bounded by all 3 layers of the true vessel wall [2]. Usually IAs grow very slowly, at less than 1 mm per year [3]. When large enough, they may rupture or cause a mass effect on adjacent tissue, causing iliac venous obstruction, which can mimic deep venous thrombosis [4]. In rare cases, IAs rupture into adjacent organs, such as the colon, the bladder, the cava, or the iliac vein, leading to massive hemorrhage or arteriovenous fistulas. Torrealba et al presented a case of a ruptured right iliac artery aneurysm with a fistula to the inferior vena cava with successful management with an endovascular graft [5]. Piljic et al reported a case of an internal iliac arteriovenous fistula caused by rupture of an atherosclerotic giant iliac artery aneurysm, with successful management with surgical repair [6]. The frequency of arteriovenous fistula resulting from perforation of an aneurysm to a vein has been reported at 3–4% for ruptured aneurysms and at 1% for non-ruptured aneurysms [7]. However, little is known about aneurysms rupturing into or communicating with another adjacent artery. To the best of our knowledge, this is the first such case to be reported.

We report a case of a large iliac saccular aneurysm communicating with a transplant renal artery. The aneurysm was successfully excluded by using covered stents in both the iliac and transplant renal arteries. IRB approval was not required for reporting this individual case. Informed consent for publication was obtained from the patient.

Case Report

A 52-year-old man was admitted for chronic left lower abdominal pain for 1 year. He underwent a renal transplantation in the left iliac fossa 21 years ago because of renal failure due to nephritis. He took Ciclosporin regularly after the transplantation. Duplex ultrasound showed an oval-shaped hypoechoic structure adjacent to the left external iliac artery (EIA), with swirling blood flow inside (Figure 1A, 1B). Computed tomography angiography (CTA) showed an aneurysm of the left EIA, with a size of 35×34×47 mm. Unusually, it also seemed to communicate with the transplant renal artery (TRA). There was calcification in the aneurysm wall without surrounding hematoma (Figure 1C–1H). Endovascular treatment was performed. Digital subtraction angiogram (DSA) of the left iliac artery showed that the aneurysm was supplied mainly by the left EIA (Figure 2A, 2B; Video 1). After implantation of a covered stent graft (8×50 mm VIABAHN Endoprosthesis, Gore) in the left EIA, follow-up DSA showed an EIA reconstructed with no contrast leak; however, contrast still flowed into the aneurysm though the TRA (Figure 2C, 2D; Video 2). A second covered stent graft (5×25 mm VIABAHN) was implanted in the TRA. Completed DSA showed successful exclusion of the aneurysm, with patent blood flow within both the left EIA and TRA (Figure 3A). The patient had complete resolution of pain following the procedure. After 1 month, duplex ultrasound showed the aneurysm to be completely excluded, with no blood flow within (Figure 3B, 3C). At 4 months, CTA showed the aneurysm had decreased in size to 32×25×23 mm, with thrombosis within it. The left EIA and TRA were patent (Figure 3D).

Discussion

IAs can be fusiform or saccular in morphology. Saccular IAs are sometimes difficult to differentiate from pseudoaneurysms. Since pseudoaneurysms are more prone to rupture, the radiologist must always suspect a pseudoaneurysm in the differential diagnosis of lesions contiguous to an artery, to avoid potential massive hemorrhage. Duplex ultrasound is a valuable tool in the diagnosis of peripheral arterial pseudoaneurysm. Some special signs may be detected, such as the “yinyang” sign and “to-and-fro” sign [8]. In this case, the IA was considered a true aneurysm because there was calcification in the aneurysm wall indicating a true vessel wall, and there was no surrounding hematoma. The patient had no history of invasive procedures or severe trauma in the 21 years after the renal transplantation. The “yin-yang” sign may also be detected in saccular true aneurysms with swirling blood flow within. CTA plays an even more important role in detection of vascular lesions or complications such as aneurysm, pseudoaneurysm, or active bleeding after surgeries or invasive procedures [9], and it can provide a useful guide for endovascular treatment.

Aneurysms that communicate with another independent artery are extremely rare. To the best of our knowledge, there are no previous reports about aneurysms “rupturing” or “eroding” into an adjacent artery, or communicating with another artery. In the present case, before the procedure, the aneurysm was considered adjacent to the TRA, but not in communication. After implantation of the stent graft in the EIA, DSA confirmed that the aneurysm also communicated with the TRA. The mechanism causing this unusual communication is unknown. Mechanisms that may contribute to iliac aneurysmal disease include proteolytic degradation of vessel wall connective tissue, inflammation, biomechanical wall stress, and molecular genetics [10]. In the IA walls there are inflammatory processes from premature lysis of fibrin filaments and entrapped red blood cells, which subsequently release cytokines, such as elastases and metalloproteinases. These factors contribute to the destruction of the aneurysm walls [11]. We assume that in this case the aneurysm initially grew from the EIA. With gradual enlargement and compression on the TRA, the aneurysm “ruptured” into the TRA due to inflammation from the aneurysm wall to the adjacent transplant renal arterial wall. This may be similar to an aneurysm rupturing into an adjacent organ, such as the digestive tract [12] or adjacent vein [5,6,13], leading to gastric intestinal bleeding or arteriovenous fistula.

IAs can be treated with coil embolization or stent graft to reconstruct the feeding artery, or open repair [14]. Such procedures are not complicated. For aneurysms communicating with multiple arteries, the challenge is identifying the multiple blood supplies through preoperative CTA imaging and to prepare for the repair of multiple communicating arteries.

Conclusions

We report a case of a rare iliac saccular aneurysm communicating with a transplant renal artery. Treatment was not complicated. The aneurysm was successfully excluded by covered stents in the iliac and renal arteries. The pathogenesis of this communication was not clear. The most important lesson was to identify possible multiple blood supplies of an aneurysm through preoperative CTA imaging, and to prepare for the possibility of reconstructing multiple arteries.