Comprehensive MRI diagnosis of sacral osteomyelitis and multiple muscle abscesses as a rare complication of fistulizing Crohn's disease.

Pelvic osteomyelitis is a very uncommon complication of Crohn's disease, usually clinically unsuspected in the setting of acute Crohn's disease relapses. The case of a 21-year old patient is reported, in whom ileo-cecal inflammatory disease was complicated by fistulization to the presacral space and sacral osteomyelitis, plus multiple abscesses involving the iliopsoas, posterior paravertebral and gluteal muscles. As confirmed by surgical and pathological findings, MRI provided comprehensive imaging diagnosis by demonstrating both the pathogenesis and the full extent of the complex, deep pelvic inflammatory process. Low back pain in patients with Crohn's disease should not be underestimated since its differential diagnosis includes serious and potentially life-threatening causes such as osteomyelitis, so prompt assessment with cross sectional imaging, particularly MRI, is necessary.