Mycotic aneurysm of the suprarenal aorta due to Streptococcus pneumoniae: case report and literature review
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* Nathalie Lussier
* Yves Girouard
* Denis Chapleau

Infected aneurysms of the abdominal aorta are relatively uncommon, accounting for only 18% of all mycotic aneurysms.1 Infection of a pre-existing atherosclerotic aneurysm after bacteremia is the most common route of infection.2 In unusual circumstances, spread from a contiguous septic process may be the cause, and it usually occurs after vascular surgery.3 Among aortic locations, aneurysms of the suprarenal aorta are less frequent than those of infrarenal origin.4

The organisms implicated vary according to location. The most likely organisms involved in cases of suprarenal aneurysms are gram-negative rods, especially *Salmonella* spp.5 Overall, gram-positive organisms account for 60% of mycotic aneurysms, *Staphylococcus aureus* and *Streptococcus* spp. occurring in 46% and 8% of cases respectively.6 In the pre-antibiotic era, *Streptococcus pneumoniae* was often implicated in subacute bacterial endocarditis. 7 Today, mycotic aortic aneurysms due to this organism are rare. Since 1966, only 8 cases have been reported.4,8–12

We describe a case of *S. pneumoniae* infection of the suprarenal aorta that occurred in association with a contiguous diaphragmatic abscess.

## Case report

A 65-year-old woman was admitted with a 2-week history of abdominal and low back pain, anorexia, weight loss and constipation. She also reported an episode of influenza-like symptoms (low-grade fever and cough) 1 month before admission. She was treated with ciprofloxacin for 14 days for a presumed pneumonia.

On admission, her temperature was 37.8 °C, and other vital signs were normal. Physical examination revealed a slightly distended but soft abdomen with reduced bowel sounds. No pulsatile mass was palpable. Cardiopulmonary auscultation was normal and the rest of the examination revealed nothing abnormal.

The findings of laboratory studies revealed only a mild leukocytosis. Abdominal plain films gave findings that were consistent with ileus, and no aortic calcification or vertebral erosions were seen. Abdominal ultrasonography revealed the presence of a saccular aneurysm of the suprarenal aorta measuring 3.7 cm in diameter and having a narrow neck. CT revealed no extension of inflammation in surrounding tissues. Arteriography identified the exact location of the defect (Fig. 1). The chest x-ray film and echocardiogram were normal.

![FIG. 1](http://canjsurg.ca/https://www.canjsurg.ca/content/cjs/42/4/302/F1.medium.gif)

[FIG. 1](http://canjsurg.ca/content/42/4/302/F1)

FIG. 1 
Abdominal aortogram showing the 3.8-cm saccular aortic aneurysm at the suprarenal level, lying below the left diaphragm.

The patient had had no fever since admission and initially did not receive any antibiotics. Blood cultures at repeated intervals were negative for any organisms. At operation, we found an intense periaortic inflammatory reaction, and the central part of the diaphragm, which was adjacent to the aortic wall, contained a small cavity filled with pus. This abscess was drained, and the aneurysm wall and all overlying tissues were debrided and resected. This procedure left an aortic defect 3 × 4 cm in dimension, which we covered with a Dacron patch. Resected tissues and pus were sent for bacteriologic analysis.

Postoperatively, the patient was treated with ampicillin, clindamycin and gentamicin until the results of the cultures were known. Gram’s staining showed gram-positive cocci in pairs. Culture of the involved aorta grew *S. pneumoniae*, the same organism isolated from pus contained in the diaphragmatic abscess. The patient was then given penicillin intravenously (2 million units every 4 hours) for 28 days.

Histologic examination of sectioned aorta showed marked inflammatory infiltration of the media and adventitia with gram-positive cocci in pairs, supporting the diagnosis of mycotic aneurysm (Fig. 2).

![FIG. 2](http://canjsurg.ca/https://www.canjsurg.ca/content/cjs/42/4/302/F2.medium.gif)

[FIG. 2](http://canjsurg.ca/content/42/4/302/F2)

FIG. 2 
Histologic examination of the aneurysm wall shows heavy inflammatory infiltration with grampositive cocci in pairs (Gram’s stain, original magnification ×650).

The postoperative course was complicated by a left hemothorax on day 12. After a thoracic drain was placed, the patient was sent for aortography, which did not reveal the source of the bleeding. The hemothorax was evacuated but no bleeding site was identified. We believed that this hemorrhagic complication resulted from diffuse oozing.

The patient recovered well. The antibiotic therapy was modified to penicillin taken orally (300 mg every 6 hours) for 2 weeks, for a total duration of 8 weeks. There was no late graft infection or pseudoaneurysm formation during a 2-year follow-up, which comprised clinical examination and CT.

## Discussion

Jarrett and associates8 first reported 2 cases of aneurysms infected by *S. pneumoniae* in a series of 17 patients with mycotic aortic aneurysms. The diagnosis was made by aneurysm wall culture or by identification of bacteria from intraluminal suppuration. No other details are available regarding these 2 patients. Considering all 17 patients in that study, the clinical presentation most commonly consisted of fever (71%), abdominal pain (35%), back pain (18%) and a palpable pulsatile mass (53%). Paraclinical data included a slight leukocytosis (65%), positive blood cultures (70%), erosion of lumbar vertebrae (18%) and an absence of aortic calcification on plain abdominal films in most patients. All patients in the series received antibiotics, and 71% also underwent operation. With respect to outcome, the authors concluded that gram-negative infections show greater virulence than gram-positive organisms, being associated with death rates of 72% and 25% respectively.

In 1983, Ewart and associates9 reported 1 case, a 48-year-old man who presented with fever associated with abdominal and back pain. Blood cultures of tissue from the aneurysm grew *S. pneumoniae* and there was no evidence of pneumonia on the chest x-ray film. Later, a pulsatile lower abdominal mass was noted, and CT revealed an infrarenal aortic aneurysm. The results of operative arterial wall cultures were not specified. Neither the type nor the duration of therapy or patient outcome were given.

Chan and associates4 also published a series of 22 patients with aortic infected aneurysms, including 2 cases in which *S. pneumoniae* was the infecting organism. One was located in the transverse aortic arch; the location of the other was not mentioned. The offending organisms were identified by blood culture or by culture of aneurysm contents, or both. Specific information for each patient was not provided. All patients were treated with surgery and antibiotics intravenously for 4 to 6 weeks. The death rate was estimated at 14% in that study.

Two other cases were described by Gelabert and Quinones-Baldrich10 and Cull and associates.11 The aneurysm in both cases was located in suprarenal aorta. The arterial wall cultures were positive in the first patient; in the second patient the diagnosis was made by blood culture. Therapy for the first patient consisted of 28 days of intravenously administered cefazolin followed by lifelong oral treatment; the second patient was given a 6-week course of antibiotics. Both patients had a good outcome.

Finally, a case of infected aortic aneurysm due to penicillin-resistant *S. pneumoniae* was reported recently by Albrecht and associates.12 This patient presented with a bacteremic pneumonia. Subsequently, meningitis developed and the patient died despite vancomycin therapy. Autopsy confirmed the presence of the organism in the aneurysm wall and meninges.

Our patient presented with the most common clinical findings, except that her blood cultures were sterile, which may have been due to the antibiotics she had received before admission. The diagnosis was made by arterial wall culture. Interestingly, the arterial wall culture grew the same organism that was isolated from the diaphragmatic abscess, suggesting that the aneurysm infection arose from this adjacent focus. It is probable that a pneumococcal left lower lobe pneumonia developed first and led to the formation of a diaphragmatic abcess, which in turn spread contiguously to the adjacent aortic vessel. This mechanism of mycotic aneurysm formation is very unusual. Brown and associates13 stated that this group constitutes less than 10% of mycotic aneurysms at all locations. Lumbar osteomyelitis, local wound infection, retroperitoneal, pancreatic and mediastinal abscesses, carcinomas and perforation of the gastrointestinal tract, infected lymph nodes and lung infections have all been reported.1,3,9,14–16 However, no case of diaphragmatic abscess was found.

The general principles of management involve both antimicrobial therapy and surgery. Drainage and wide débridement of all devitalized tissues with thorough revascularization in situ or extra-anatomic bypass grafting are necessary. The procedure chosen depends on the location of the aneurysm, the purulence observed and the surgeon’s preference. The graft can be made with autologous tissue or with prosthetic material. In the present case, there were 3 reasons for using a prosthetic Dacron patch instead of autogenous tissue to correct the defect left by the aneurysm resection. First, the defect was large and would have required a vessel much larger than saphenous vein. Second, by the time the aneurysm was resected, the patient was unstable and speedy closure was essential. Finally, experience has been gathered from cardiac valvular surgery, ascending thoracic aortic surgery and infected infrarenal aortic surgery showing that, given appropriate débridement, prosthetic material can be left in place. Our patient was operated on rapidly after the aneurysm was identified, and her postoperative course was complicated by a hemothorax, which necessitated a second operation. Leaking from the anastomosis site is a well-known complication of aortic angioplasty reconstruction, and graft revision in the early postoperative period is required in 2% of patients.17

So far, there are no good prospective studies establishing the optimal duration of antibiotic therapy after surgical resection of mycotic aneurysms. Most authors agree that at least 6 to 8 weeks are mandatory;1,7,13 and some state that patients should be placed on lifelong therapy.2,5,18 The recent increase in antibiotic resistance could be partly explained by overexposure of bacteria to antibiotics, and prolonged treatment could add to this resistance. Finally, the side effects of long-term treatment for this condition must be weighed against the benefits for patients, and these benefits are not evident at present. For these reasons, the treatment for each patient must be individualized. In our case, the patient was treated with antibiotics intravenously for 28 days, followed by oral treatment for 4 weeks, for a total duration of 8 weeks. She had a good outcome and did not experience any late complications.

The results after treatment of infected aneurysms have improved over the years because of prompt diagnosis, improved surgical techniques and advances in antimicrobial therapy. Today, the death rate related to suprarenal mycotic aneurysms is estimated to be 13%.10 Recently, a new problem has arisen: the emergence of penicillinresistant strains of *S. pneumoniae*. From an epidemiologic point of view, this occurrence will lead to a modification of our empiric and long-term antibiotherapy regarding this agent and may further complicate the management of such infections. Mycotic aneurysms due to penicillin-resistant *S. pneumoniae*may also carry a higher morbidity and mortality, as in the patient described by Albrecht and associates12 who had a particularly fulminant postoperative course.

*   Accepted December 18, 1997.

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