This report describes a 66-yr-old woman with no medical history of vascular or gastrointestinal disease who presented with massive gastrointestinal bleeding secondary to a primary AEF (PAEF). Surprisingly, this diagnosis was not made with repeated enhanced CT scan but was only confirmed at the time of operation.
This case highlights two important issues. First, although PAEF are not the most common cause of gastrointestinal bleeds, their existence must not be forgotten. Indeed, PAEF is a life-threatening cause of upper gastrointestinal bleeding that may affect patients with no history of vascular disease. Second, diagnosis of PAEF may be difficult (2) and radiological techniques are not totally reliable.
Secondary AEF, which account for the majority of AEF, are complications of reconstructive abdominal aortic surgery. Commonly, the fistula is the result of infection near the proximal anastomosis between the aorta and the prosthesis. PAEF, which are extremely rare, are usually the result of erosion of a preexisting AAA and rupture into the gastrointestinal tract. This is often associated with an inflammatory or infective aortitis (3), which was not found in our patient; however, PAEF in the absence of inflammation has also been reported (1). In our patient, the assumption is that an undiagnosed atherosclerotic AAA had eroded into the adjacent duodenal wall and eventually led to a gastrointestinal bleed. Indeed, atherosclerosis remains the most common etiology, accounting for more than 3/4 of the cases reported (4). Moreover, para-aortic radiation therapy can, in uncommon cases, lead to PAEF with histological signs of radiation damage (4).
It is common for AEF to present initially with a minor, so-called “herald” bleed, which is later followed by a catastrophic, life-threatening bleed (1). This was the sequence of events in our patient’s case. It is also possible that, in her case, the two episodes of bleeding may have been unrelated. The first, minor, episode may have been a result of the documented esophagitis, whereas the second may have been a complication of the OGD. Visceral perforation is a known complication of OGD (although esophageal perforation is far more common than duodenal) (5); it is less common in diagnostic than in therapeutic OGD. Logically, if visceral perforation can occur, an AEF can also be formed, although this complication has not been reported (5). Unfortunately, in our patient’s case, it was impossible to tell whether the AEF was genuinely primary or secondary to the initial OGD.
Both PAEF and secondary AEF are difficult to diagnose, and the same diagnostic tests are used (although suspicion should be increased in patients with a previous AAA repair). More information is available regarding the use of diagnostic tests in secondary AEF. Therefore, in the discussion of AEF and diagnostic tests these two conditions will be considered together.
In the past, OGD was considered to be the most useful diagnostic test (6,7), although it is not, in fact, reliable in establishing the diagnosis (8). Aortoangiography has also been used but is not always useful (9), as noted in our patient. Nevertheless, this technique may be useful to define arterial anatomy and to allow the planning of aortic reconstruction. At present, enhanced CT is thought to be the diagnostic modality of choice (10). However, in our patient even this examination did not definitively confirm the communication between duodenum and aorta (Fig. 1). Our finding is in line with a few reports in which CT scan did not help and in which the diagnosis was made at the time of emergency laparotomy (11,12).
The sensitivity and specificity of CT scan in detecting AEF have not been prospectively studied (13–15). Two studies have compared CT scan findings with operative results and concluded that this examination has a sensitivity of 94% and a specificity of 85% in detecting AEF (14,16). One report demonstrated that a three-phase CT (delayed scan) is able to visualize the extravasating contrast media from the aorta to the duodenum and the late opacification of the bowel by blood coming from the aorta (17). Indeed, the presence of dye in the duodenum when IV contrast has been given has already been used to affirm the diagnosis of PAEF (18). In our patient, it was later noted that on each occasion that the CT scan was performed, the patient’s mean arterial blood pressure was <60 mm Hg. This may have accounted for the lack of sensitivity of this examination in this particular patient—the decrease in the gradient between systemic arterial blood pressure and abdominal pressure may have affected the flow of the contrast between the aneurysm and the duodenum.
In conclusion, even if CT scan is at present considered to be a valuable tool for diagnosing PAEF, suspicion is the most important diagnostic aid to prevent the overlooking of this rare and often fatal disease. In the context of hemodynamic instability, emergency surgery should be performed in all cases of gastrointestinal bleeding associated with an abdominal aneurysm.
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