Background: Primary aortoenteric fistula (AEF) is a communication between the native aorta and any portion of the gastrointestinal (GI) tract. It is a rare and catastrophic complication of abdominal aneurysms with an incidence of approximately 0.04 to 0.07%. Due to the rarity of condition and variable clinical presentation, most patients die before arriving at the accurate diagnosis with an overall mortality rate of 61-100% and decreases after surgery to the rate of 30-50%.
Case: We report a case of a 42 year-old male, hypertensive, diabetic, who was referred to our institution for intermittent abdominal pain and episodes acute lower gastrointestinal bleeding six weeks prior to admission. The bleeding stopped spontaneously and the patient was managed conservatively to a local hospital. During his admission at the said institution, a colonoscopy was done which revealed no abnormal findings. A whole abdominal computed tomography (CT) scan with triple contrast was subsequently done which revealed the presence of a fusiform infrarenal abdominal aortic aneurysm with possible dissection. He was eventually transferred to our institution where a CT aortogram revealed the presence a 3.7x4.8 cm infrarenal abdominal aortic aneurysm with a focal dissection (as shown in Figure 1C). A sinus tract connecting the sigmoid colon to the infrarenal aortic aneurysm with collection of fluid and gas locules around the infrarenal aorta were likewise noted (as shown in Figure 1A-B). On review of the past medical history, the patient is being treated for pulmonary tuberculosis for the past 4 months; hence, a mycotic aneurysm was highly considered. Isoniazid and rifampin were continued and patient eventually underwent extra-anatomic bypass with axillo-bifemoral graft (as shown in Figure 2D). Post-operatively, IV Ceftriaxone and Metronidazole were continued. An intra-operative aortic wall tissue gram stain, culture, TB-PCR and Syphillis test were all negative. Histologic examination of the sigmoid revealed focus disruption of the normal continuity of the mucosal layer with the muscle layer replaced by granulation tissue and submucosal bleed. Microsections of the mesentery show formation of fibrotic nodules with areas of cholesterol granuloma composed of scattered gold-brown (hematoidin) crystals, cholesterol clefts engulfed by multinucleated giant cells, several macrophages, leucocytic infiltrates and fibrinoid material, which do not show bacterial colonies on gram stain and acid fast bacilli on AFB stain. Since the cultures were negative, antibiotic therapy was discontinued after 2 weeks. On the 21st post-operative day, patient was discharged in good clinical condition.
Conclusion: This is a case of a rare type of primary aorto-enteric fistula involving the sigmoid colon that was successfully managed by extra-anatomic bypass and sigmoidectomy.