Secondary aorto-enteric fistula: a case report and review of literature

Abstract

Aorto-enteric fistula (AEF) is an uncommon but potentially fatal condition that is important to identify early because early diagnosis and aggressive management can reduce mortality. We report the case of a 73-year-old man with a history of aorto-bifemoral bypass grafting who was admitted for investigation of tiredness and lethargy. He passed melaena on the day of admission with an associated drop in haemoglobin. Initial upper gastrointestinal endoscopy revealed no significant abnormality. Later in the admission he again passed melaena, this time in large amounts. A repeat endoscopy identified a defect in the duodenal mucosa with visible Dacron graft. The patient went on to suffer another large bleed from which he could not be resuscitated. Our report highlights a fatal manifestation of aorto-enteric fistula, and reviews the associated literature.

BACKGROUND

This case highlights the importance of considering a diagnosis of aorto-enteric fistula in any patient with a history of aortic grafting who presents with gastro-oesophageal bleeding.

CASE PRESENTATION

The patient was admitted to hospital feeling lethargic and having “gone off his legs”. He had a significant past medical history of arterial disease, having had a coronary artery bypass (1996), carotid endarterectomy (1997) and, most recently, an aortic–bifemoral bypass (1998). He had made a full recovery from all of these procedures.

INVESTIGATIONS

On the day of admission, the patient’s blood pressure was 143/63 mm Hg, pulse rate 95 beats/min, and his abdomen soft and non-tender. He had a witnessed episode of melaena at the time of admission and his haemoglobin dropped from 11.5 g/dl to 9.7 g/dl over the next 24 h. He remained haemodynamically stable.

The patient was transfused with two units of blood and urgently investigated with an upper gastrointestinal (GI) endoscopy. This demonstrated gastric erosions with no evidence of significant GI bleeding.

OUTCOME AND FOLLOW-UP

On the fourth day of admission, he suffered a large episode of melaena with a drop in blood pressure to 77/58 mm Hg and loss of peripheral pulses. He was resuscitated with colloidal fluids and blood, and his haemoglobin after transfusion of two units of blood was 5.4 g/dl. A further transfusion of four units of blood was commenced. A repeat upper GI endoscopy demonstrated a defect in the third part of the duodenum with an underlying Dacron graft (fig 1) consistent with an aorto-enteric fistula (AEF). An urgent computed tomography (CT) scan of the abdomen was arranged, but the patient suffered a further large GI bleed and cardiac arrest from which he could not be resuscitated.

Figure 1.

The anatomical location of the aorto-enteric fistula in the third part of the duodenum, overlying the Dacron graft.

DISCUSSION

AEFs were first described by Sir Ashley Cooper in 1817,² defined as a direct communication between the aorta and GI tract. There are two types of AEFs—primary and secondary. Primary AEFs form spontaneously in the absence of prosthetic aortic material. Secondary AEFs are fistulas in the presence of prosthetic aortic material, and were first described by Brock in 1953.³

Secondary AEFs usually occur some years after the aortic reconstructive surgery, but can present from 6 months to more than 10 years.¹ It is thought to be associated with chronic low grade infection of and around the graft, possibly secondary to suture line failure.^4,5 Over a period of time this can lead to the formation of a fistula. Additionally direct mechanical erosion of the intestinal wall by the graft itself has been described.¹ In 80% of cases the AEF involves the duodenum, particularly the third portion because it is relatively fixed.⁵

AEFs usually present with a “herald” bleed, manifesting either as melaena, haematochezia or haematemesis, which may occur intermittently for several days.¹ This GI bleed is usually minimal and does not cause any haemodynamic instability. The “herald” bleed is controlled by clot formation but can be followed by a catastrophic bleed.⁴ This second bleed is thought to occur when the clot dislodges or lyses as a result of high aortic arterial pressures. At this time, the patient may suffer from upper abdominal pain or back pain. Patients can also present with an unexplained fever secondary to recurrent graft infection.⁶

A high index of suspicion is required for an early diagnosis of AEF, with a good history providing the most important clue. Most AEF are in range of the endoscope and this investigation is also useful because it will exclude other causes of upper GI bleeds. Enhanced abdominal CT scans are another useful investigation for AEF⁷ because they are readily available and provide an accurate evaluation of the aorta and the surrounding retroperitoneal tissues. Though there are no formal comparisons of the different imaging modalities, ultrasound scans are not believed to be as useful as CT scanning for this purpose because they may not visualise this region as clearly.

Secondary AEF is a surgical emergency. Survival without intervention is poor, and can be improved to 14–70%⁸ with surgical treatment. Conventional treatment consists of prosthetic excision and extra-anatomic bypass with bowel suture or resection. This procedure has a 12 and 24 month survival rate of 60% and 50%, respectively.⁹ There is also increasing interest in the role of endovascular stenting in the management of AEF in those patients with significant morbidity.¹⁰

LEARNING POINTS

• Secondary aorto-enteric fistula (AEF) must be considered in any patient presenting with a gastrointestinal (GI) bleed and a history of aortic surgery.

• The majority of all secondary AEF are in range of an upper GI endoscopy, but can sometimes be missed with this investigation.

• Abdominal computed tomography is a useful investigation for secondary AEF.

• Secondary AEF has a high mortality without surgical intervention.