Acute gastrointestinal bleeding due to primary aortoduodenal fistula: Report of two rare cases - TÜTÜN, Ufuk; AKSÖYEK, Ayşen; ULUS, Ahmet Tulga; PARLAR, Ali İhsan; GÖL, M. Kamil; BAYAZIT, Murat (Turkish Journal of Gastroenterology, 2004)