1. Department of Gastroenterological and Pediatric Surgery, Oslo University Hospital, Ulleval, Kirkeveien 166, 0407 Oslo, Norway
2. Faculty of Medicine, University of Oslo, P.O. Box 1072 Blindern, 0316 Oslo, Norway
3. Department of Radiology, Oslo University Hospital, Ulleval, Kirkeveien 166, 0407 Oslo, Norway