Sharp abdominal pain/nausea/vomiting. ct shows cbd dilated 11-12mm. bc normal. no jaundice no weight loss. no gallbladder. lesion near ampulla-cancer?

Possible: Yes, cancer near the ampulla is a possibility, but you could have an infection, scar tissue, or other problem. You will likely need ERCP, a type of scope procedure to tell what it is for sure. Good luck!

Maybe, or not...: Could be scarred bile duct, impacted stone (even without a gallbladder). Will need additional testing, e.g. MRCP and/or ERCP. The former is an MRI scan of the area; the latter is an advanced endoscopy technique which allows for biopsy, and stenting through obstruction.