Woman, around 83 age, with rheumatoid arthritis and large hiatus hernia came with one-day history of severe abdominal pain and vomiting. She was tachycardic and tachypnoeic. Abdominal examination revealed tenderness and peritonism to her right iliac fossa. Her bowel sounds were diminished.

WBC count was 16.1g/dL, and plain abdominal radiographs revealed no perforation or obstruction. I think of gallstone. What diagnosis and further treatment do you suggest?