Magnetic resonance imaging evaluation of osteoid osteoma: utility of the dark rim sign

Background While typical patterns of osteoid osteoma have been described on CT, MRI findings can overlap among different diseases, and atypical patterns exist. In this study, we assessed the presence of a novel dark rim sign and its utility in the MRI diagnosis of osteoid osteoma. Objective The purpose of this retrospective study was to assess the utility of the dark rim sign seen on MRI in children with osteoid osteoma. Materials and methods MRI studies from 36 pediatric patients with osteoid osteoma and a control group of patients with either osteomyelitis or stress fracture were analyzed and then compared for the presence of the dark rim sign. Patients from the osteoid osteoma group were further divided based on nidus location and evaluated for the presence of the dark rim sign. Results The relationship between the dark rim sign and osteoid osteoma was statistically significant ( P