Case of ruptured Staphylococcus aureus aortitis: presentation and management

Abstract

Infectious aortitis with the complication of aortic aneurysm carries a high mortality rate without appropriate interventions, mostly due to aortic rupture. For this reason, early and prompt diagnoses along with surgical and medical managements play critical roles. Aortic infection with Staphylococcus aureus (SA) is uncommon, but reported cases have been usually associated with fatal complication from rapid progression into rupture. We report a 65-year-old man who developed methicillin-sensitive SA aortitis and then aortic rupture. Patient was successfully treated with staged vascular repair and long-term antibiotic use.

Background

Aortitis is closely associated with inflammatory changes in aortic wall, caused by both infectious and non-infectious aetiologies. Non-infectious causes include necrotising aortitis with giant cells and diffuse aortitis associated with an increased risk of systemic inflammatory disease,¹ while infectious sources can stem from bacterial seeding from trauma or other sites of infections.² Organisms associated with infectious aortitis include Staphylococcus, Enterococcus, Streptococcus and Salmonella.³ If untreated, aortitis can lead to formation aneurysm and potentially rupture, which carries high mortality.⁴ However, the clinical manifestation and optimal management of Staphylococcus aureus (SA)-associated aortitis remain poorly understood. Here, we present a 65-year-old man with extensive history of atherosclerotic diseases presented with methicillin-sensitive SA (MSSA) aortitis that rapidly progressed to aortic aneurysm and rupture. The case illustrates our experience of the diagnostic evaluation, complication and successful treatment of this uncommon but serious condition.

Case presentation

The investigation was performed in our institution during January 2017 to February 2018. The procedures, including research on identifiable human material and data, abide to the National Institutes of Health guideline of human studies and Declaration of Helsinki for medical research involving human subjects. Patient consent was also obtained.

Patient is a 65-year-old man who was transferred to our hospital for acute onset of lower back pain that started 1 day ago along with nausea and lower abdominal pain. His other medical conditions include diabetes, hyperlipidaemia, hypertension, coronary artery disease with prior coronary artery bypass graft. One year ago, patient underwent right common femoral to mid-posterior tibial artery open in-situ bypass using saphenous vein for peripheral vascular disease. The vascular bypass surgery was complicated by postoperative infection with fluid collections around the graft, and culture showed Enterococcus faecalis and Klebsiella pneumonia. He underwent wound debridement and treatment with antibiotics with no subsequent recurrence. At the time of presentation, he denied any recent invasive procedures, skin or soft tissue infection, or drainages from the previous bypass site.

Patient was found to be febrile up to 40.2°C requiring 3 L nasal cannula oxygen, but with normal blood pressure and heart rate in 80–90 bpm. Physical examination showed tenderness along bilateral paravertebral region along lumbar spine and an extensive scarring along previous bypass site in the right leg without signs of infection. Rest of the examination was unremarkable.

Investigations

Initial laboratory showed white blood count (WBC) of 5.2×10⁹/L (normal 4-9×10⁹/L) with 76% neutrophil (normal 41%–67%) and 12% bandaemia (normal 0%–11%). Erythrocyte sedimentation rate was 38 mm/hour (normal 0–15 mm/hour) and C reactive protein was 92.5 mg/L (normal <8 mg/L). The patient underwent CT angiogram of the chest, abdomen and pelvis, which was remarkable for generalised atherosclerosis, and para-aortic stranding along infra-renal aorta and retroperitoneal fat, suggestive of aortitis (figure 1). Further investigation into possible viral and bacterial sources of aortitis, as well as immunological disorders was initiated. The rapid plasma reagin and treponema pallidum antibody, hepatitis panel along with rheumatological workup were unremarkable. Initial blood cultures from the referring hospital were negative; however, repeat blood cultures taken from our centre showed MSSA. Transoesophageal echocardiogram did not reveal evidence of endocarditis.

Figure 1.

Initial CT angiogram from the referring hospital. There is soft and calcified atheromatous plaque throughout the aorta, especially within the abdominal and infrarenal aorta. There is a moderate amount of stranding surrounding the infrarenal aorta and extending within bilateral retroperitoneal fat.

Differential diagnosis

Initial differential diagnosis included viral and bacterial aortitis, autoimmune vasculitis, Takayasu’s arteritis and rheumatoid arthritis.

Treatment

Though uncommon, the patient was found to have MSSA aortitis. He was initially treated with broad-spectrum agent; antibiotics were then narrowed down to intravenous cefazolin based on culture sensitivity. Despite aggressive medical management, patient continued to have abdominal and back pain, fever and positive blood culture. A repeat CT of the abdomen obtained 7 days from prior CT showed ruptured aortic aneurysm (figure 2) and he proceeded to an emergent vascular surgery intervention. The patient underwent a staged procedure with initial endovascular repair of ruptured abdominal aortic aneurysm with Gore Excluder device (26×14×14 main body via the left with a 12×10 mm contralateral limb via the right), followed by aorto-bi-iliac reconstruction with homograft and explant of the endograft, 6 days later. Postoperatively, he was monitored in intensive care unit with resuscitation. He developed acute kidney injury due to renal hypo-perfusion, which was treated with resuscitation without the need for renal-replacement therapy. The final culture of the aortic aneurysm sac also grew MSSA, confirming the diagnosis.

Figure 2.

Repeat CT angiogram 7 days after initial imaging. There is significant interval increase in size of posterior periaortic density with aortic rupture posteriorly at the level of the infrarenal abdominal aorta and extending to the level of the bifurcation.

Outcome and follow-up

After a prolonged hospital course, patient gradually recovered his renal function and was able to tolerate regular diet. He was discharged from hospital on day 27, with a course of intravenous cefazolin followed by life-long suppressive oral cephalexin 500 mg every 6 hours. One year after discharge, he is currently doing well with no recurrence of the MSSA aortitis.

Discussion

In previous publications, SA aortitis has been reported.^{2 5} Our observation adds to this pool of diagnosis and treatment of the SA aortitis, highlighting the importance of early diagnosis and surgical management. MSSA aortitis is uncommon and carries high mortality rate without prompt intervention.⁶ The risk factors for mortality include female, extremes of age, SA infection, aneurysm rupture, lack of surgical interventions, aneurysm located above renal arteries and extensive infection around periaortic site.⁷ Typically, diagnosis is through CT scans, which show wall thickening, periaortic fluid collection or soft tissue inflammation, sometimes air within the wall.⁸ More importantly, infectious aortitis can rapidly progress into aneurysm or pseudoaneurysm, leading to various complications including hydronephrosis from obstruction, aortoenteric fistula, abscess and more seriously, aortic rupture.⁸ Yague et al reported a case of MSSA aortitis concurrently with retroperitoneal fibrosis and persistent bacteraemia. The disease was unresponsive to antimicrobial therapy alone and eventually led to aortic rupture and death.²

Our case demonstrates the case of rapid development of aneurysm in MSSA aortitis diagnosed by serial CT scans, and highlights the importance of prompt diagnosis of the pathogen leading to infectious aortitis along with early surgical intervention. In addition to the positive blood cultures obtained initially, tissue sample obtained during surgical repair of aortic aneurysm is equally critical. This information would help to optimise choice of antibiotics and its duration following surgery particularly in preventing recurrence. Finally, in suspected case of MSSA aortitis, repeating blood cultures and close monitoring with serial CT images are necessary to monitor responses to treatment, and prevent fatal complication of aortic rupture.

Learning points.

• Though uncommon, Staphylococcus aureus as a source of infective aortitis should be considered, especially among patients with multiple co-morbidities.

• Repeat imaging should be performed along with early intravenous antibiotic use in patients presenting with infectious aortitis.

• In case of high risk for aortic rupture, early surgical intervention may be favoured with endovascular aneurysm repair as a bridging procedure before definitive repair with vein graft.