Mycotic thoracoabdominal aneurysms

Primary mycotic thoracoabdominal aortic aneurysms (MAAs) are a small subset of all aortic aneurysms, but left untreated are almost invariably fatal from rupture (1-3). Historically, the gold standard of treatment was wide surgical debridement and in-situ or extra-anatomical repair. Mortality rates of up to 40 per cent are associated with open surgical repair (1,4,5). This poor outcome may be as a result of the plethora of medical comorbidities, magnitude of surgical insult and presence of sepsis encountered in these patients. The treatment of this life-limiting condition has been subject to evolution in line with the advent and acceptance of stent-graft technology and the development of open surgical adjuncts to stenting-hybrid surgery (6). Furthermore it has been suggested in the literature and is our belief that infection of the native aorta and super-infection of an aortic graft are differing disease entities and as such should be managed differently. This is reflected, perhaps anecdotally, in the re-infection rates reported in one series of endovascular repairs of native thoracic aortic infections vs. infected grafts [6.3% vs. 50%; P=0.08 (7)]. Mycotic aneurysms are defined by the presence of two or more of the following features: sepsis (fever, leucocytosis and pain), positive blood culture, positive culture from the aneurysmal wall, or characteristic radiological appearance (including irregular aortic wall, rapid growth rate, or saccular appearance of the aneurysm). Negative blood cultures and absence of pyrexia do not exclude the diagnosis when the patient has presented with signs of infection and had characteristic radiological findings but had already been commenced on antibiotics. We will discuss in turn the pitfalls and hazards of modern treatment of primary MAAs, according to anatomical location in line with the Crawford classification (8). There has been lack of clarity in reporting outcomes from true descending thoracic aneurysms (DTAs) in which the proximal and distal stent landing zones do not impinge upon the origin of arch and/or visceral arteries, and type I thoracoabdominal aneurisms (TAAAs) (9). We will discuss descending thoracic aneurysms as a separate entity to true type I TAAA as outcomes will patently be very different. We believe that clarity in description of these aneurysms treated is essential in the evolution of our knowledge in how MAAs are best managed (Figure 1). Figure 1 Crawford classification of thoracoabdominal aneurysms Descending thoracic aneurysms The advent of thoracic endovascular aneurysm repair (TEVAR) graft technology has transformed the management of mycotic aneurysms. Semba et al. were the first to describe endovascular repair of three mycotic DTAs in combination with antibiotic therapy. They reported no perioperative mortality and no complications from persistent bacteraemia at median follow-up of 24 months (10). TEVAR has reduced the 28% (11) mortality associated with open repair to as low as 11% to 15% (12,13). Some medium-term follow-up data post-TEVAR for MAA reports patients alive as long as 83 months with a survival of 73% at median follow-up of 20 months (13). Complications reported to be associated with TEVAR for mycotic DTAs include perioperative rupture, stent migration, and malposition with a type I endoleak (14) (Figure 2). Figure 2 A. Computed tomography of a mycotic thoracic aortic aneurysm; B. Three-dimensional reconstruction demonstrating successful exclusion with an endograft Kan et al. performed a systematic review of endovascular treatment for mycotic aortic aneurysms. They included 16 abdominal and 32 thoracic aneurysms, of which only one was ostensibly thoracoabdominal (15). The 30-day mortality, due to sepsis or massive bleeding, was 10.4% (five patients). There were five late mortalities (10.4%), two died of cardiac disease, and three died with graft-related bleeding problems. The 12-month actual survival rate of the healed group was 94.0±4.0%, and that of the persistently infected group was 39.0±17.0%. There was no significant influence of aneurysm location. Interestingly, age ≥65 years, rupture of the aneurysm (including aortoenteric fistula and aortobronchial fistulae), and fever at the time of surgery were identified as significant predictors of persistent systemic infection, defined as fever, signs of sepsis, or haemorrhage. Pre-operative use of antibiotics for longer than one week and an adjunct procedure combined with EVAR were identified as significant protective factors for persistent infection. However, by multivariate logistic regression analysis, the only significant independent predictors of persistent systemic infection identified were rupture of aneurysm and fever. In our reported series of four ruptured and one intact mycotic DTA, TEVAR was associated with one perioperative death and one type II endoleak, which spontaneously resolved, over a mean follow-up period of 30.5 months (6). Despite the theoretical risks of infection of the stent graft, the surgical insult associated with explanting a TEVAR and performing open surgery once sepsis has subsided renders this impossible. TEVAR for mycotic DTA should be considered the definitive procedure rather than an adjunct to deferred open surgery. Ortner’s syndrome - recognition and management An unusual complication of TEVAR is compression of the left recurrent laryngeal nerve as it hooks around the arch of the aorta (16-19). The most sensitive region of that of the ductus arteriosus and aneurysm of a patent ductus arteriosus has been described as a cause of Orter’s syndrome (20,21). The left vocal cord will adopt a paramedian position and cause hoarseness of voice. This is can be due to an aneurysm itself (22) or acute sac expansion following sac thrombosis subsequent to stent deployment (23). In one reported case, the hoarseness of voice actually improved following endovascular treatment of a saccular aneurysm (24). There is no particular strategy to obviate from acute sac expansion post-stenting; however it is important to be cognizant of this potential problem and aware that the condition is likely to improve with conservative management.