Multidisciplinary Management of Ruptured Mycotic Internal Iliac Aneurysm with Iliaco-Colonic Fistula: A Case Report

Introduction

Mycotic aneurysms, accounting for approximately 0.65% of all aneurysms, are a rare and life-threatening condition primarily caused by bacterial infections. These infections often occur in individuals with compromised immune systems or pre-disposing factors such as bacterial endocarditis, intravenous drug use, or arterial trauma[1–3]. Unlike degenerative aneurysms, mycotic aneurysms expand rapidly due to active infection, making them highly prone to rupture, which is associated with significant morbidity and mortality risks [1,4]. Internal iliac artery aneurysms are uncommon, representing less than 2% of intra-abdominal aneurysms [5]. When infected, these aneurysms present serious challenges, as their rupture can lead to severe complications, such as bleeding and shock [6]. This condition requires prompt intervention, often involving a combination of endovascular embolization, open surgical repair, and prolonged antibiotic therapy to control infection and stabilize the patient [7–9]. This case report describes an 84-year-old man with a left internal iliac artery aneurysm that progressed over several years before suddenly enlarging and rupturing, causing life-threatening complications. The case underscores the complexity of managing such rare vascular pathologies and highlights the importance of an individualized, multidisciplinary treatment approach.

Case Report

CASE HISTORY AND PAST INTERVENTIONS:

The patient’s aneurysm was first incidentally detected in December 2019 during follow-up imaging for chronic diverticulitis of the sigmoid colon. This condition eventually required a laparoscopic sigmoid resection in January 2020 due to complications. Imaging at the time of the aneurysm diagnosis revealed bilateral aortoiliac ectasia, including a partially thrombosed aneurysm of the left internal iliac artery measuring 27 mm. In May 2020, the patient underwent bilateral transabdominal preperitoneal (TAPP) hernia repair to address symptomatic inguinal hernias. This procedure, like the earlier sigmoid resection, was uncomplicated, and the patient made a full recovery.

Subsequent follow-up imaging, including a CTA in May 2020, demonstrated minimal progression of the aneurysm, now measuring 30 mm. After extensive discussion, the patient chose continued surveillance rather than prophylactic surgical or endovascular intervention. The narrow left iliac bifurcation, the large internal iliac artery aneurysm, and the need to sacrifice the left internal iliac artery posed significant challenges to endovascular options, including the risk of gluteal claudication. Open surgery was also deemed high-risk, with a long recovery period. Therefore, regular monitoring was established. He was maintained on medical therapy, including statins, aspirin, and blood pressure management. By March 2021, the aneurysm had grown slightly to 35 mm, but the patient remained asymptomatic. After detailed discussion, conservative management was continued, and follow-up through 2022 and 2023 confirmed the aneurysm remained stable without significant changes.

ACUTE PRESENTATION:

In early August 2024, the patient presented to the Emergency Department with shock due to severe lower gastrointestinal bleeding. Initial imaging, including CTA of the abdomen, revealed a dramatically enlarged left internal iliac aneurysm measuring 61 mm (Figure 1), with evidence of a fistula between the aneurysm and the sigmoid colon, which was identified as the source of the gastrointestinal bleeding. The aneurysm was now suspected to be mycotic due to the presence of gas within the aneurysmal sac and adjacent fluid collections, indicating infection. There was also evidence of left ureteral compression, leading to obstruction of urine flow.

EMERGENCY INTERVENTION:

On the day of admission, the patient underwent emergency exclusion of the ruptured aneurysm, which had fistulized into the sigmoid colon. This procedure involved coil embolization of all internal iliac artery branches and stent grafting from the left common into the external iliac arteries (Figures 2, 3). The embolization successfully controlled the bleeding and stabilized the patient hemodynamically. A sigmoidoscopy performed 2 days later revealed external compression of the descending colon (15–18 cm from the anus) caused by the aneurysm. Three ulcerations with hematin coverage were observed, 2 with fistulous openings. The largest fistula, at 13 cm from the anus, was associated with confluent ulceration, making endoscopic closure unfeasible. The colorectal anastomosis from the 2020 sigmoid resection, located 10 cm from the anal verge, appeared intact and was below the lowest ulceration.

SURGICAL MANAGEMENT:

A few days later the patient underwent open surgery to resect the fistula and control the aneurysm. The procedure included preoperative double-J catheter for better ureter identification, followed by laparotomy, adhesiolysis, and separation of left ureter. Left common iliac and external iliac arteries were exposed, followed by Hartmann’s procedure with resection of the neo-rectosigmoid below the former anastomosis and later end colostomy (Figure 4). The fistula was opened by colon resection, followed by resection and debridement of the internal iliac aneurysm, which was filled with pus and stool components. Additionally, the common and external iliac arteries were exposed on a longer distance and clamped. Complete resection of the iliac axis including the stent graft was performed. The thrombotic material was evacuated, and the aneurysm sac was extensively debrided and flushed. A physician-made 7-cm-long bovine pericardial tube graft was used to reconstruct the left iliac axis, connecting the proximal common iliac artery to the middle segment of the external iliac artery (Figures 5–7). Rectoscopy with wash out of the rectal stump was performed. An omentum patch was created to cover the graft, to separate the left ureter, and to cover the pelvic cavity and the rectal stump. Two drains were placed to allow rinsing.

MICROBIOLOGICAL FINDINGS AND ANTIBIOTIC THERAPY:

Intraoperative biopsy samples taken from the aneurysm and surrounding tissues revealed a polymicrobial infection, with organisms including Citrobacter freundii and Escherichia coli, supporting the diagnosis of a mycotic aneurysm. The patient was started on broad-spectrum intravenous antibiotic therapy immediately upon admission. The initial regimen consisted of co-amoxicillin administered intravenously for one week. This was followed by a short course of intravenous piperacillin/tazobactam before escalating to imipenem.

CURRENT STATUS AND FOLLOW-UP:

The patient was discharged in stable condition and transferred to a rehabilitation clinic 6 days postoperatively. During rehabilitation, the antibiotic regimen was adjusted to ertapenem intravenously with oral ciprofloxacin and doxycycline, later simplified to oral ciprofloxacin and clindamycin after discharge. Regular follow-up CT imaging showed resolution of most gas-fluid collections adjacent to the iliac prosthesis within weeks. The left double-J catheter was removed without complications, and a subsequent colorectal evaluation confirmed excellent clinical condition. The patient has adapted well to the stoma. The therapy with clindamycin and ciprofloxacin was successfully discontinued as planned after 12 weeks, following an uneventful clinical course and normal findings on abdominal CT imaging. For now, regular follow-up remains our primary focus. Initially, these are scheduled every 3 months in collaboration with vascular surgeons and infectious disease specialists. Depending on the clinical course and favorable outcomes, the intervals may be gradually extended.

Discussion

Rupture of internal iliac artery aneurysms is rare but carries a high mortality rate, especially when complicated by infection and fistula formation, as observed in this patient. Laine et al reported that conservative management with regular surveillance of internal iliac artery aneurysms can be considered in select patients, particularly those with smaller aneurysms or significant comorbidities [5]. However, our case demonstrates that even with regular monitoring, rapid changes can occur, leading to rupture and fistulization into adjacent structures such as the colon.

The treatment strategy combined endovascular and surgical interventions to stabilize the patient and address the underlying infection, guided by considerations of durability, infection resistance, and long-term outcomes.

Initial stabilization was achieved through endovascular intervention. Endovascular techniques are widely regarded as the first step in managing acute bleeding in cases of ruptured aneurysms. Endovascular repair provides rapid hemodynamic stabilization and hemorrhage control and serves as a bridge to definitive surgical treatment. It reduces immediate surgical risks and allows stabilization before open surgical intervention. However, as the infection is not addressed by endovascular techniques alone, these measures must be followed by radical debridement and reconstruction to ensure long-term success [9–11].

Various surgical approaches were discussed, starting with alternatives to in situ repair, which included autologous vein grafts, cryopreserved allografts, and synthetic grafts. These options were carefully evaluated but ultimately deemed less suitable for this patient. Autologous vein grafts, while associated with low infection rates (0–16%) and low graft occlusion rates (0–9.1%), present several limitations. Their use is technically demanding, particularly in elderly patients with systemic vascular disease. Additionally, the harvesting process prolongs the operation, increasing the risk for patients with serious comorbidities. Vein harvesting is also associated with postoperative venous complications, such as chronic venous insufficiency (up to 15%) and deep vein thrombosis (up to 22%) [12].

Cryopreserved allografts offer low reinfection rates but have their own drawbacks, including a risk of late aneurysmal degeneration and rupture, reported in up to 5.9% of cases. Furthermore, their limited availability, particularly in emergency settings, reduces their practicality for urgent vascular reconstructions [12]. Synthetic grafts, including rifampicin-bonded and silver-coated variants, are readily available and have broad antimicrobial activity, but reinfection rates for these grafts remain approximately 11% within 2.5 years. Their efficacy is reduced in highly virulent infections involving pathogens such as MRSA or Candida spp., making them less suitable for extensively contaminated settings [12,13].

The option of an extra-anatomical bypass, such as a femoralfemoral or axillofemoral bypass, was also considered but ultimately deemed suboptimal. While these bypasses avoid direct reconstruction in infected areas, they do not restore physiological blood flow and are associated with lower long-term patency rates compared to anatomical reconstruction. Extra-anatomical bypasses are linked to higher rates of thrombosis and complications, often necessitating frequent reinterventions [14–16].

Given these limitations, a bovine pericardial graft was chosen for in situ reconstruction following extensive debridement of the infected field. According to the literature, bovine pericardial grafts are advantageous in contaminated fields due to their ready availability, resistance to infection, and adaptability for complex reconstructions. Studies by Kreibich et al and Czerny et al report favorable outcomes with bovine pericardium, including low reinfection rates and excellent mechanical compatibility with native vessels [17,18].

Despite these advantages, bovine pericardial grafts are not without limitations. Studies explicitly evaluating their long-term performance remain limited. Available evidence highlights complications localized to anastomotic sites, such as aneurysms (4.8%), stenoses (3%), and graft limb occlusions (1.2%). Most complications occur within the first year, often after a median of 9 to 11 months, and are primarily managed with endovascular interventions such as stent grafting. Importantly, no degeneration or stenosis unrelated to the anastomoses has been observed in the graft material itself, suggesting strong structural durability. Freedom from graft-related complications is estimated at 91% at 1 year and 87% at 5 years, demonstrating acceptable long-term outcomes but emphasizing the need for close follow-up [19].

These results align with findings from other biological grafts, such as cryopreserved allografts, which have been associated with anastomotic disruption, aneurysmal degeneration, and thrombotic complications. Autologous vein grafts, while demonstrating lower infection and thrombosis rates, may still experience rupture or occlusion. Compared to these alternatives, bovine pericardial grafts appear to provide a durable solution in high-risk, infected fields, but further studies are needed to confirm their advantages in broader patient populations [19].

Antibiotic therapy is an essential additive treatment in managing mycotic aneurysms, complementing surgical intervention. Early administration of broad-spectrum antibiotics, followed by targeted therapy, is critical to controlling infection and preventing reinfection, as emphasized by Dix et al and Müller et al [2,7]. In our case, a prolonged antibiotic regimen, in combination with surgical debridement, played a key role in the patient’s recovery and reducing the risk of recurrence.

Conclusions

This case illustrates the complexity of managing mycotic aneurysms, which can lead to or occur as a complication of gastrointestinal fistulization. It underscores the necessity of a multi-disciplinary approach that combines endovascular and open surgical techniques alongside removal of the source of infection and targeted antibiotic therapy. Early diagnosis and prompt intervention were crucial in controlling life-threatening complications and achieving a successful outcome. The use of a bovine pericardial graft for vascular reconstruction provided a durable solution in an infected field, highlighting its utility in complex vascular cases. This case further emphasizes the importance of individualized treatment strategies, especially for high-risk patients, where coordinated efforts between vascular and colorectal surgeons, infectious disease specialists, and interventional radiologists can significantly impact patient survival and recovery.