Internal iliac aneurysm: an unusual cause of acute abdomen pain – case presentation and brief review

Abstract

Internal iliac aneurysms (IIAs) are a rare group of intra-abdominal aneurysms that, if not diagnosed and treated promptly, can lead to significant morbidity and mortality. We present a case of an elderly Chinese male who presented acutely with abdominal pain due to a leaking left IIA. Prompt diagnosis and expedient treatment with a hybrid approach, i.e. with endovascular balloon occlusion followed by surgical excision of the IIA, led to an excellent outcome. Case presentation is followed by a brief discussion of the current literature on the management of this elusive condition.

Introduction

Intra-abdominal aneurysms (IAAs), including aortoiliac and visceral aneurysms, are insidious pathologies that can lead to surgical catastrophes. Their inconspicuous nature frequently causes a low index of suspicion and delay in diagnosis that can lead to dire consequences. Internal iliac aneurysms (IIAs) are no exception, as they are extremely rare and are usually undetectable by clinical examination unless they are of a significant size, emerging from within the pelvic cavity to be palpable. We present the case of a patient presenting with acute abdominal pain due to a leaking IIA. He was promptly diagnosed and treated operatively with a hybrid open-and-endovascular approach.

Case presentation

An otherwise healthy 84-year-old Chinese man presented with one day of abdominal pain which started in the left flank, associated with constipation. He denied any fever or urinary symptoms. Clinical examination was remarkable for left iliac fossa tenderness without peritoneal signs. He had a leukocytosis with total white count of 21 × 10⁹/L. All other blood laboratory investigations were unremarkable.

The patient was treated empirically with intravenous antibiotics with a presumptive diagnosis of acute diverticulitis, but he remained tachycardic. A computed tomography (CT) scan of the abdomen and pelvis was performed to rule out intra-abdominal sepsis. The scan proved to be life-saving as it showed an irregularly shaped left IIA with associated ascites, suspicious for hemoperitoneum from a contained leaking aneurysm (Figure 1). He was resuscitated further and taken to the operating room expediently for control of bleeding and definitive repair of his leaking IIA.

Figure 1.

Axial CT scan of pelvis, showing large IIA (thick white arrow) with displacement of the sigmoid colon (thin white arrow).

The approach to surgery was a hybrid endovascular and open operation. While the traditional principles of vascular surgery still apply, i.e. proximal and distal vascular control prior to definitive vascular repair, resection, or reconstruction, vascular control can be achieved quicker with endovascular balloon occlusion at the site of vascular injury. This is afforded by present-day excellent quality CT-scan images that can accurately identify the point of extravasation and availability of intra-operative fluoroscopy imaging systems that allow endovascular procedures such as angiography and angioplasty balloon tamponade to be performed (Figure 2). Once in position, the angioplasty balloon can be inflated for immediate vascular control or left deflated in cases where the vessel is not actively bleeding, thus allowing continued perfusion to the corresponding lower extremity. This adjunctive technique can minimize blood loss and improve visibility and ease of operative dissection toward the vascular pathology especially in the deep narrow pelvis with structures adhered consequent to a marked inflammatory response. Following endovascular control via the left common femoral artery (Figure 3), the angioplasty balloon was inflated across the ostia of the left internal iliac artery. The aneurysm rupture involved the proximal left internal iliac artery, between the main ostia and anterior/posterior division branch bifurcation, without extension on to the common femoral segment. A lower midline laparotomy revealed a large, ruptured left IIA, with extremely friable walls, and hemoperitoneum. There was a thick rind adherent to the adjacent structures signifying a marked inflammatory process. The left iliac veins were not visualized beneath this rind. Surgical control, proximally and distally, was attained after which endovascular balloon occlusion was removed. The IIA was excised followed by over sewing of the transected ends with 4-0 polypropylene sutures. The left internal iliac artery was left unreconstructed due to the suspected infected field. The pelvic organs otherwise appeared well-perfused from an intact right internal iliac artery. The abdomen was closed after placement of a closed-suction drain in the pelvis, and the patient was transferred to the high-dependency unit for post-operative care.

Figure 2.

Pelvic angiogram with access via left common femoral artery showing filling of the left IIA (thick white arrow) off the left common iliac artery (thin white arrow).

Figure 3.

Endovascular control of bleeding with balloon occlusion utilizing an angioplasty balloon (white arrow).

Intraoperative tissue from the IIA was sent for microbiological culture, which revealed Group B Streptococcus (GBS). He was treated with 14 days of intravenous ceftriaxone and subsequently converted to oral co-amoxiclav for six weeks, according to sensitivity. Post-operative course was complicated by deep vein thrombosis (DVT) treated by thrombolysis and balloon venoplasty. He subsequently made a full recovery.

Discussion

Isolated IAAs are exceedingly rare with less than 200 cases of IIA reported in the literature, accounting for only 0.3–0.4% of all IAAs. ¹

IIAs commonly affect elderly males and have a male:female ratio of 6:1. While much rarer in women, they tend to affect younger patients with recent pregnancy or delivery, making them an important subgroup. ² Risk factors for IIA are poorly characterized and are thought to be similar to that of abdominal aortic aneurysms (AAA). ² Although they are deemed to share similar risk factors, a prior history of AAA repair has not been shown to be associated with increased development of IIA. ³ Mycotic IIAs have been reported and numerous pathogenic micro-organisms are identified, including Staphylococcus aureus, Klebsiella spp., Pseudomonas spp., and Salmonella spp.^4,5 Our patient is an elderly male with age-appropriate atherosclerotic disease, evidenced by scattered aortic wall calcification on CT scan but without an AAA. He had an isolated mycotic IIA due to an uncommon pathogen, GBS.

IIAs are true pelvic aneurysms hidden within the depths of the pelvic cavity, thus making diagnosis a challenge until after they present as a complication. Brin and Busuttil suggested that up to 43% of IIAs are asymptomatic hence they can escape detection altogether. ² Symptoms are often non-specific and can be secondary to compression of surrounding structures by the aneurysm. Iliac artery thrombosis has been reported in 5% cases of IIA and, rarely, external compression from the aneurysm has been shown to cause obstruction of the iliac veins with resultant limb swelling or DVT. ⁶ In our patient, the desmoplastic reaction from the IIA likely caused a stenosis of the common iliac vein confluence that gave rise to the development of his iliofemoral DVT. Another rare IIA symptom is constipation due to external recto sigmoid compression. ⁷ It is interesting to note that our patient had constipation upon acute presentation and had CT-scan evidence of colorectal compression (Figure 1).

IIAs are associated with very few specific findings on abdominal examination due to their deep location, unless they are exceedingly large. A pulsatile mass can be detected during digital rectal examination in patients 20–50% of the time.^8,9 This finding was not present in our patient.

CT scanning of the abdomen and pelvis with contrast is the gold standard investigation for diagnosis of IIA, ¹⁰ as it can provide accurate anatomic location and reveal the presence of any complications such as rupture or compression of adjacent organs. Trans-abdominal ultrasonography is unreliable as it can be operator dependent and inaccurate, especially in the pelvic region with poor visibility due to overlying bowel gas. Trans-anal or trans-vaginal ultrasound scanning can detect IIA more readily and may have a place in diagnosis and monitoring IIA.

IIAs can be morbid entities as they present with rupture and exsanguination in nearly one third of cases, with the exact incidence varying between 33% and 38%, ⁸ and a mortality rate in excess of 50%. ² IIA diameter does not necessarily correlate with rupture risk, making serial monitoring with imaging less appealing compared to AAA. ² IIA diameter of ⩾3 cm has been suggested by some investigators as a threshold for intervention in asymptomatic IIA. ¹¹

Surgical management of this elusive condition has evolved considerably. Open proximal ligation of the IIA has largely been abandoned due to its unacceptably high recurrence of approximately 33%. ² Formal exclusion and excision of the aneurysm is standard of care. Due to limited surgical access in the narrow pelvis and possible intense fibrotic reaction caused by the aneurysm, open repair can be fraught with danger. Iatrogenic injury to pelvic veins and bleeding may occur with associated mortality reported to be in excess of 50%. ² Acute interruption of the hypogastric circulation by surgical ligation, especially in the setting of contralateral atherosclerotic occlusive disease, may result in of gluteal ischemia/necrosis and/or rectosigmoid ischemia. ¹² In such instances, revascularization of at least one internal iliac artery or IIA repair with an interposition graft is recommended. IIAs can also be managed with endovascular techniques, such as covered-stent repair with preservation of perfusion, or coil embolization to induce thrombosis.^13–15 We propose that a hybrid open endovascular approach can be successfully used to treat IIA, as illustrated above.

Conclusion

IIAs are rare IAAs that are usually asymptomatic but can present complicated with rupture or compression of adjacent organs. Their deep pelvic location often eludes clinical detection and rupture is associated with a grave prognosis. Open, endovascular, or a hybrid repair approach is safe and effective while early diagnosis and decisive intervention are fundamental to successful treatment with excellent outcomes