This is a 11-years old boy who had fever and abdominal pain. USG showed a retroperitoneal left para-aortic mass, confirmed by CT scan. A PET/CT was done to look for other lesions in the body, but this was the only one.

The CT guided biopsy was easy to do in the prone position, under sedation with an 18G coaxial biopsy gun.

The initial diagnosis was inflammation. Then they looked for IgG4 and found some features that suggested IgG4 disease. Eventually, a multi-disciplinary discussion confirmed that diagnosis but it took some time and effort to get there. IgG4 is not an easy diagnosis to make.