Retroperitoneal and iliopsoas abscess as Crohn's disease onset mimicking a common lumbosciatic pain.

Crohn's Disease (CD) refers to a chronic transmural bowel inflammation affecting a range between 5 and 15 per 100,000 person-years worldwide 1. In patients with stricturing CD, the transmural pattern of inflammation may trigger the development of sinus tracts able to connect to other tissues, leading to the formation of fistulas or abscesses 2. Intra-psoas abscesses are rare, affecting between 0.