Teaching Case

A 68-year-old male patient presented to the Emergency Department with rectorrhagia. A colonoscopy was performed showing fresh blood with clots in the right colon and active bleeding from the appendiceal base. The patient had previous history of open repair of an infrarenal aortic aneurysm 4 years prior. On examination, tachycardia and hypotension were present.

MDCT-angiography showed an infrarenal aorto-aortic graft with a saccular pseudoaneurysm in its anterior wall, surrounded by a hypodense periaortic soft tissue mass (Figure 1). The soft tissue mass had lobulated margins and there was stranding of the periaortic fat. It showed heterogeneous attenuation with a slightly hyperattenuating area by its right margin on non-enhanced images that did not enhance in arterial and venous phases (Figure 2). These features were consistent with acute haematoma without signs of active bleeding. Moreover, the tip of the vermiform appendix was adhered to the periaortic mass (Figures 2 and 3), with loss of the fat plane between both structures. No gas was detected.

A postsurgical MDCT-angiography performed 4 years earlier did not show any of these findings (Figure 4).

Aortoenteric fistulas (AEF) are life-threatening conditions. They may be primary or secondary.  Primary AEF are usually associated with a preexisting aortic aneurysm and are very rare. Secondary AEFs (SAEF) occur as complications of aortic reconstructive surgery [1, 2]. In 80% of cases, the communication is established with the duodenum, mostly third and fourth portions, due to its retroperitoneal location [3]. Unusually, the fistula can develop with the stomach or the appendix (as in the case shown). It has been postulated that a combination of chronic low-grade infection of the aortic graft and repetitive pressure on the intestine from aortic pulsations leads to the formation of these fistulas [1].

Clinical suspicion is crucial. In patients with gastrointestinal bleeding and a history of previous aortic graft, a SAEF should always be suspected. Other symptoms such as sepsis, abdominal or back pain and groin or abdominal pulsatile mass have also been described.  

On CT, it is important to distinguish normal postsurgical findings from signs of infection. Infection may occur from 2 days to 26 years after surgery [3]. Soft tissue oedema and ectopic gas are common findings after surgery, but the presence of ectopic gas after 3-4 weeks or soft-tissue thickening after 2-3 months should be considered an infection [1]. Other CT findings include: focal bowel wall thickening, lost fat plane between the bowel and the aorta (the most frequent, almost 100%), breach of the aortic wall, extravasation of intravascular contrast material into the bowel lumen (the most specific but extremely rare) and leakage of enteric contrast material into the periaortic space (a rare but direct sign of aortoenteric fistula). If a hyperattenuating collection is seen in the unenhanced phase, as in this case, an acute haematoma should be suspected.

Treatment of SAEF has classically been open surgery repair, but nowadays endovascular management has emerged as a more conservative alternative in patients of advanced age or with comorbidities [2, 4]. Our patient was treated with endoluminal stent-graft placement and posterior surgery which confirmed the fistula. Appendicectomy and removal of the inflammatory mass, described as a periaortic abscess, were performed. The patient developed a recurrent infection, underwent open aortobi-iliac bypass but passed away.

Written informed consent from the patient’s family has been obtained for publication.