A known case of familial Mediterranean fever, presented with retroperitoneal periaortic soft tissue mass/sheet-like lesion, that was found to be retroperitoneal fibrosis. 

There are two types: 

• primary (idiopathic): 2/3 of cases

  • a manifestation of systemic autoimmune or inflammatory diseases

• secondary: 1/3 of cases

  • most commonly due to medications, neoplasms

FDG PET-CT

• not useful as a primary diagnostic tool due to low specificity

• allows detection of remote sites of disease

• may help guide biopsy and assess treatment response

Top differential diagnoses

• chronic periaortitis

• retroperitoneal metastases and lymphoma

• coagulopathic ("retroperitoneal") hemorrhage

• inflammatory abdominal aortic aneurysms