"altered anatomy in post-surgical states (e.g. Billroth II gastrojejunostomy, Roux-en-Y jejunostomy) 4"
"Pneumobilia is common post-ERCP and may be present even when the history of the procedure is remote (especially if a sphincterotomy has been performed)."
"sphincterotomy (e.g. sphincter of Oddi dysfunction or stenosis)"
"structural abnormalities of oesophagus, stomach or duodenum 4"