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We report a case of a sixty year old man with a mycotic infra-renal abdominal aortic aneurysm complicated by a left psoas abscess. After treatment with parenteral antibiotics he underwent early aortic reconstruction with an in-situ prosthetic graft wrapped in an omental pedicle. Mycotic abdominal aortic aneurysms can be treated in this way despite the potential for graft infection from persisting retroperitoneal sepsis.
A 60 year old male attended A&E with an eighteen month history of intermittent night sweats. He had suffered one episode of rigors and associated confusion and reported having recently lost three kilograms in weight. He reported no other symptoms.
His past medical history included gastro-oesophageal reflux disease, hypercholesterolaemia, atrial fibrillation and a cerebrovascular accident in 2006. In 2008 he presented with bilateral acute ischaemic legs. He was in atrial fibrillation and was found to have bilateral popliteal emboli subsequently undergoing successful popliteal embolectomies. During that admission, MR and CT angiography demonstrated mild atheroma with possible overlying thrombus at the aortic bifurcation. CT angiography six months later showed that a significant amount of the aortic thrombus had resolved. This raised the possibility of a previous localised distal aortic dissection or saddle embolus.
Medications included lansoprazole 30 mg, sotalol 80 mg, rosuvastatin 20 mg and warfarin. He had been a heavy smoker having stopped six years ago.
At presentation he was found to be haemodynamically stable with a temperature of 37.9 °C. No obvious source of infection was found on clinical examination. He had a normal full blood count and renal function with only slightly deranged liver function tests.
Chest radiography and abdominal ultrasound scan were unremarkable. An echocardiogram did not identify any valve vegetations or atrial thrombus. Protein electrophoresis revealed a diffuse hypergammaglobinaemia.
He was discharged after undergoing a bone marrow biopsy. Three blood cultures during his admission were negative and the bone marrow aspirate and trephine biopsy were normal. He was booked for an outpatient CT chest, abdomen and pelvis.
The following day he attended A&E with a short history of haematuria and left sided loin pain. His white cell count and renal function were normal. A CT KUB showed no evidence of renal tract calcification or ureteric dilatation. However there was loss of definition around the lower aorta with increased density in the periaortic fat. The aorta was not dilated and the appearances suggested an inflammatory process.
Contrast enhanced CT showed an abnormality in the left psoas muscle and the adjacent soft tissue around the distal end of the aortic bifurcation. The appearances were suggestive of a psoas abscess. There was also a focal dilatation of the distal aorta just proximal to the bifurcation with a small amount of surrounding soft tissue suspicious of aortitis (Fig. 1).
He was initially treated empirically with intravenous vancomycin which was subsequently changed to meropenem on advice from the Microbiologists. His symptoms rapidly settled with normalisation of his temperature and inflammatory markers.
A CT aortogram 12 days later showed deterioration with aneurysm formation of the distal aorta. The inflammatory collection within the left ilio-psoas muscle had however resolved (Fig. 2).
After two weeks of intravenous antibiotic treatment, given the radiological evidence of a weakened, dilating aortic wall, he underwent repair of his distal aorta.
At operation two separate saccular aneurysms were identified just above the aortic bifurcation. The left side was a pseudo-aneurysm with complete loss of the posterior aortic wall. Both aneurysms were full of fresh thrombus with a moderate amount of laminar thrombus within the more proximal infra-renal aorta. Both iliac arteries were soft and disease free.
All intra-luminal thrombus and aortic wall was sent for microscopy, culture and sensitivity. The aortic wall was excised leaving a posterior strip which was covered with an omental pedicle. The bifurcation was replaced with a rifampicin soaked Dacron bifurcation graft with end to end anastomosis to the infra-renal aorta and both common iliac arteries (Fig. 3). After completing the anastomoses the graft was wrapped with a second omental pedicle.
He made a good post-operative recovery and was discharged home two weeks later on oral antibiotics for a further two months. Tissue cultures proved to be sterile.
On review he is asymptomatic with normal inflammatory markers and a CT scan seven months post procedure shows no evidence of infection or inflammation.
Mycotic aortic aneurysms are rare but are associated with a high morbidity and mortality. The incidence has decreased and the aetiology has changed since the more widespread use of antimicrobials. Where once embolic seeding from cardiac valves was the principal cause now invasive vascular procedures and intravenous drug abuse have become more frequent causes. Commonly isolated organisms include Salmonella, Staphylococcus and Escherichia coli.1
The diagnosis of such cases can prove challenging. In one study less than half of the patients presented with the typical triad of a mycotic aortic aneurysm, namely, fever, pain, and a pulsatile mass.2
Mycotic aneurysms are associated with significantly more problems than non-infected aneurysms. There is an increased risk of rupture and of postoperative graft infections.3 In addition, aortic infection complicated by psoas abscess is associated with higher incidence of emergency operation, hospital mortality, prosthetic graft infection, and aneurysm-related mortality than infection without an accompanying psoas abscess.4 There are few previously cases of aortic infection complicated by a psoas abscess and the incidence of psoas abscess in patients with a mycotic aortic aneurysm has been reported at 4–20%.5–13
Ideally, before surgery is undertaken, the patient should be apyrexial, blood cultures sterile and inflammatory markers normal. Surgical management in the form of wide debridement and resection of the infected aorta and the surrounding infected tissue followed by distal revascularization together with long-term antibiotics has been the standard treatment.
Some authorities insist that extra-anatomic vascular bypass grafting is mandatory, others prefer an in situ prosthetic graft.14,15 The extra-anatomic route is promoted as it is believed that placement of synthetic vascular graft in the infected bed will inevitably lead to graft infection. The disadvantages are of a decreased graft patency and risk of aortic stump rupture. In situ grafting is thought to counter these problems but it has been questioned whether or not it is safe to perform in an infected field.15
Studies have now shown that excellent results are possible with in situ grafting given appropriate antimicrobial therapy combined with correct surgical technique. There is some evidence that harvested superficial femoral vein has a greater resistance to infection. Long term graft infection is reported at 5–21% at 17–48 months.16–19
One procedure that has been suggested to help reduce infection is covering the prosthetic graft with a pedicled omental flap.2,3 Its use has also been suggested in those patients developing graft infection in whom graft removal is deemed too risky. The exceptional structure and function of omentum has long been used by surgeons. It provides a rich blood supply with a high absorptive capacity aiding the clearance of bacteria and foreign material. It can promote angiogenic activity in structures to which it is closely applied, supporting ischaemic and inflamed tissues. It has an innate immune function, aids lymphatic draining and promotes haemostasis. It has been used to close gastrointestinal perforations, aid haemostasis in liver resections, reconstruct defects in the head and neck, chest wall and perineum, and to protect exposed arteries.20
We feel that if an in situ prosthetic graft is to be used, the essential components of the surgical technique are debridement of as much potentially infected tissue as possible and then “sandwiching” of the graft between 2 separately constructed pedicles of omentum. Prolonged postoperative antibiotics seem intuitively good sense but little evidence exists regarding length of treatment.
The authors declare no conflict of interest.
Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.