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Ann Thorac Surg 1996;61:1053-1054
© 1996 The Society of Thoracic Surgeons
University of Zurich, Zurich, Switzerland
Mycotic aneurysm is an unusual, life-threatening pathologic entity that encompasses a spectrum of different types of arterial infection associated with high morbidity and mortality. The optimal operative treatment, the length of antimicrobial therapy, and even the appropriate use of the term are not well established and remain controversial.
Initially used to describe arterial infection caused by septic emboli from infective endocarditis, the term ``mycotic aneurysm'' presently means (1) infectious erosive arteriitis with false aneurysm caused by infection of the aortic wall but without preexisting aneurysm or (2) manifest infection in a preexisting aneurysm, which can be caused by all microorganisms, not only by fungi. In patients without aneurysmatic dilatation of the aorta the terms ``infected false aneurysm,'' ``infected aneurysma spurium,'' and ``acute bacterial aortitis'' are synonyms for the historical term ``mycotic aneurysm.'' Bacterial colonization of the contents of an aneurysm without clinical and histologic signs of infection appears relatively frequently, and should not be considered a mycotic aneurysm. Aneurysms of the aortic root and aortic annulus abscesses also do not belong to this entity. Furthermore, infection at a particular aortic or arterial site after a previous vascular or cardiac operation such as an infected anastomotic aneurysm, prosthetic graft infection, or aortoduodenal fistula without previous mycotic aneurysm should not be considered a mycotic aneurysm.
There are usually two different surgical options for operative treatment of mycotic aneurysm: either extraanatomic or in situ reconstruction. Although the surgical decision can be influenced by the location of arterial infection, the patient's general condition and immunologic state, the type of bacteria causing infection, and local findings, there is no clear indication for a certain operative technique, and the decision is usually made according to the surgeon's preference. The standard principle-extraanatomic reconstruction-requires multiple operations to restore the natural direction of blood flow, whereas in situ reconstruction offers a definitive solution by a single operation. In recent years in situ reconstruction has received emphasis [1–6].
The standard surgical principle for the treatment of mycotic aneurysm consists of aortal or arterial ligation, excision of all infected tissue including changed aortic or arterial tissue, and extraanatomic bypass grafting through a clean noninfected plane [7, 8]. Although the patency rate of extraanatomic axillofemoral bypass grafting is not excellent, this operation is usually a sufficient procedure for older patients, and in this group of patients it is usually the only treatment. Younger patients in good condition after extraanatomic grafting for mycotic aneurysm of the abdominal aorta can be considered for descending aorta-to-iliac or femoral bypass grafting through a left lateral thoracotomy, without intervention on the abdominal aorta [9].
In some cases extraanatomic bypass grafting is difficult or even technically impossible because of mycotic aneurysm location close to the heart (the ascending aorta) or the origins of the great vessels (the aortic arch, the suprarenal aorta) requiring in situ reconstruction. In situ insertion of an aortic conduit homograft is a novel method for treatment of mycotic aortic aneurysm and infected aortic grafts, which might reduce the late postoperative infection rate and improve survival of this group of high-risk patients. The preliminary results are encouraging [10–13]. This therapeutic concept has been adopted from other similar infectious conditions such as aortic annular abscess or aortic valve endocarditis. The use of homograft cryopreserved tissue has already been proved in cardiac surgery [14]. When used for infective processes of the aortic valve, it reduces the postoperative infection rate and improves survival [15]. An aortic homograft can be harvested from the descending thoracic aorta of donors during heart harvesting for transplantation. The entire aorta with its branches should be harvested for further cryopreservation during the harvesting of other organs from a donor. If stored as bank tissue, it might be used for an emergency operation because a mycotic aneurysm is usually ruptured when diagnosed. At implantation, the intercostal arteries arising from the grafts are ligated by clips, and then the grafts are inserted with end-to-end anastomoses in the usual manner using polypropylene continuous suture. In the case of a small mycotic aneurysm with a localized infection of the aortic wall, the aortic defect can be replaced with an autologous, homologous, or xenopericardial patch. If the destruction or infected changes take a larger part of the aortic wall, an aortic conduit homograft can be used for in situ reconstruction. A homograft as a composite graft is recommended for a mycotic aneurysm of the ascending aorta accompanied by aortic root infectious changes or aortic annulus abscess, or when the aneurysm is located in the proximal aorta. Prosthetic graft as a patch or vascular conduit is the last choice, and should be used only when the other possibilities are not available.
The principle of extraanatomic reconstruction avoids use of bypass procedures in a contaminated region because of the great risk of graft infection. The risk of reinfection and a life-threatening complication, such as suture line disruption, remains increased, independent of the type of operation. Aggressive local debridement of the aneurysmal wall and infected local tissue is essential to minimize postoperative infection. Coverage of the infected and anastomotic area with the omentum or muscle flap is an additional measure to protect the suture line from reinfection by enhancing microbiological resistance. The use of local antibiotic therapy can also help prevent local infection [16]. The optimal length of systemic antimicrobial therapy has not been clearly defined, and antibiotic therapy recommendations range from several weeks to a long time or even lifelong [1, 6]. In situ aortic homograft replacement for mycotic aneurysm might be considered analogous to aortic valve replacement for bacterial endocarditis, and the antimicrobial therapy is based mainly on contemporary treatment guidelines for endocarditis, with 4 to 6 weeks of intravenous antibiotics.
Increased experience in aortic surgery and good results with homograft implantation in cardiac surgery enable the revival of the old surgical concept of homograft arterial reconstruction. Improved methods of homograft preservation might reduce or prevent late homograft structural deterioration such as aneurysmal dilatation or calcification. The concept of in situ reconstruction with an aortic homograft and short-term antibiotic therapy seems more acceptable than in situ reconstruction with a synthetic graft and prolonged or even lifelong antibiotic therapy. This promising concept in reconstructive arterial surgery needs support of larger clinical series with extended follow-up.
Footnotes
Address reprint requests to Dr Pasic, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, D-13353 Berlin, Germany.
References
This article has been cited by other articles:
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  J. Kpodonu, J. P. Williams, V. G. Ramaiah, and E. B. Diethrich Endovascular management of a descending thoracic mycotic aneurysm: mid-term follow-up Eur. J. Cardiothorac. Surg., July 1, 2007; 32(1): 178 - 179. [Abstract] [Full Text] [PDF]
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 M. Idir, R. Denisi, M. Parrens, R. Roudaut, and C. Deville Endarteritis and false aneurysm complicating aortic coarctation Ann. Thorac. Surg., September 1, 2000; 70(3): 966 - 968. [Abstract] [Full Text] [PDF]
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S. Kuki, K. Taniguchi, S. Miyagawa, and H. Takano Multiple mycotic arch-thoraco-abdominal aortic aneurysms: a successful case of in situ graft replacement Eur. J. Cardiothorac. Surg., February 1, 2000; 17(2): 184 - 186. [Abstract] [Full Text] [PDF]
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T. Katsumata and S. Westaby Homograft Aortic Replacement for Infected Mediastinal False Aneurysm Ann. Thorac. Surg., November 1, 1997; 64(5): 1464 - 1466. [Abstract] [Full Text]
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Y.-F. Chen, P.-Y. Lin, H.-W. Yen, and C.-C. Lin Double Mycotic Aneurysms of the Ascending Aorta Ann. Thorac. Surg., February 1, 1997; 63(2): 529 - 531. [Abstract] [Full Text]
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