A woman with a history of cholelithiasis presents with acute abdominal pain radiating to the back. What is the most likely cause of her symptoms?

The symptoms described—a history of cholelithiasis (gallstones) and acute abdominal pain radiating to the back—suggest that the patient may be experiencing biliary colic or a complication related to gallstones. In this context, the most likely cause of her symptoms is ampulla of Vater obstruction.

The ampulla of Vater is where the common bile duct and main pancreatic duct enter the duodenum. If a gallstone becomes lodged at this site, it can obstruct both the flow of bile from the gallbladder as well as pancreatic juices from the pancreas. This obstruction can lead to inflammation of the pancreas (pancreatitis) and may also cause severe abdominal pain that radiates to the back, as the pain associated with pancreatitis often presents in this manner.

Additionally, obstruction at the ampulla of Vater can disrupt the normal digestive process, leading to changes in bowel function and additional abdominal discomfort. The clinical presentation aligns closely with the potential effects of a gallstone in this particular location, making it the most plausible explanation for her acute symptoms.