A Patient With Abnormal Abdominal CT Scan Findings

A man with a history of nephrolithiasis and laparotomy for trauma had left flank and left upper quadrant pain. He had mild leukocytosis, but the physical examination and other laboratory testing were unremarkable; abdominal CT revealed a well-circumscribed, extraluminal mass with central high density. What is the diagnosis and what would you do next?
Source: JAMA - Journal of the American Medical Association - Category: General Medicine Source Type: research