Image of the Week: Severe abdominal pain and a swollen knee in a young female

A 19-year-old female exchange student presents to the emergency department with severe abdominal pain and a swollen right knee. She has had recurrent episodes of abdominal pain for the past 5 years that last for 2 to 3 days. Previous investigations, including radiographs, CT, endoscopy, and an exploratory laparoscopy, have all failed to identify a cause. On examination, she has ...