Aortoenteric Fistula on 99mTc Erythrocyte Scintigraphy

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Aortoenteric Fistula on ^99mTc Erythrocyte Scintigraphy

N. P. Lenzo, T. A. Male and J. H. Turner

Royal Perth Hospital Perth, West Australia, Australia
Fremantle Hospital Fremantle, West Australia, Australia

There are many causes of gastrointestinal hemorrhage. The diagnosiscan be elusive, and several investigations may be required beforethe source is found [1]. We present a rare cause of gastrointestinalbleeding that was initially difficult to diagnose but was subsequentlyrevealed on a ^99mTc erythrocyte study.

Over a period of 4 months, a 70-year-old man who had undergoneabdominal aortic aneurysm repair in 1997 presented with intermittentrectal bleeding and recurrent anemia. Repeated endoscopic examinationsof the upper and lower gastrointestinal tract revealed mildpeptic ulcer disease thought insufficient to account for thedegree of anemia the patient had been experiencing. A CT scan(Fig. 6A) showed a 2-mm microbubble of gas between the distalaortic graft anastomosis and an adjacent thickened loop of gut.This finding was evident on images from adjacent CT slices andon repeated images taken 30 min apart; it was thought to be suggestiveof aortoenteric fistula or graft infection. Findings of further investigations—includingan aortogram, a celiac and superior mesenteric arteriogram,and a small-bowel barium study—were normal. The WBC was normal,and there were no clinical symptoms or signs of infection. TheCT signs alone were considered insufficient to justify explorativesurgery.

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Fig. 6A. —70-year-old man admitted for rectal bleeding and hypotension. CT scan of abdomen shows microbubble of gas (arrow) at aortic graft anastamosis anterior to aortic lumen, with anterior adjacent loop of gut.

Two months later, the patient was readmitted with brisk rectalbleeding and hypotension. A ^99mTc-labeled autologous erythrocytestudy was performed within 2 hr of the patient's presentation(Figs. 6B,6C,6D). No site of bleeding was visualized duringthe initial 60 min of imaging, but after 85 min, radionuclidesuddenly appeared over the position of the abdominal aorta andentered the small bowel. A presumptive diagnosis of an aortoentericfistula was made.

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Fig. 6B. —70-year-old man admitted for rectal bleeding and hypotension. ^99mTc erythrocyte studies show active bleeding arising over abdominal aorta rapidly transiting loops of ileum. B was obtained anteriorly at 65 min of imaging; C, at 85 min; and D, at 90 min.

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Fig. 6C. —70-year-old man admitted for rectal bleeding and hypotension. ^99mTc erythrocyte studies show active bleeding arising over abdominal aorta rapidly transiting loops of ileum. B was obtained anteriorly at 65 min of imaging; C, at 85 min; and D, at 90 min.

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Fig. 6D. —70-year-old man admitted for rectal bleeding and hypotension. ^99mTc erythrocyte studies show active bleeding arising over abdominal aorta rapidly transiting loops of ileum. B was obtained anteriorly at 65 min of imaging; C, at 85 min; and D, at 90 min.

At surgery, the ileum was found to be adherent to the aorticgraft. Blunt dissection revealed an aortoileal fistula, whichwas repaired. A culture of the resected graft grew ${alpha}$ -hemolyticstreptococci and Klebsiella oxytoca. The patient was treatedwith broad-spectrum antibiotics and had an uneventful recovery.

This patient illustrates the difficulty of diagnosing aortoentericfistulas and the fact that gas seen adjacent to a graft on CTscans is highly suggestive of an associated infection or fistula [2].Infection and aortoenteric fistulas are rare complications ofabdominal aortic aneurysmectomy and grafting [3]. Although infectionwas the likely precipitant of the development of the fistulain our patient, infection is not always the cause [3]. To ourknowledge, the scintigraphic appearance of a massive gastrointestinalhemorrhage associated with an aortoenteric fistula has not beenpreviously reported. The images aided the surgical team by revealingan aortic site of bleeding and the severity of the problem athand.

References

Rockey DC. Primary care: occult gastrointestinal bleeding. N Eng J Med 1999;341:38 -46[Free Full Text]
Rossi P, Arata FM, Salvatori FM, et al. Prosthetic graft infection: diagnostic and therapeutic role of interventional radiology. J Vasc Interven Radiol 1997;8:271 -277[Medline]
Hallett JW Jr, Marshall DM, Petterson TM, et al. Graft-related complications after abdominal aortic aneurysm repair: reassurance from a 36-year population-based experience. J Vasc Surg 1997;25:277 -284[Medline]