Simple Bone Cyst with Mesenchymal Proliferation Involving Epiphysis of the Proximal Fibula

Epiphyseal involvement of a simple bone cyst (SBC) is rare. Furthermore, its pathological variant is even more uncommon. Herein, we report a case of a 22-year-old woman with an SBC containing unusual mesenchymal tissue proliferation with epiphyseal involvement in the proximal fibula. Magnetic resonance imaging showed a cystic lesion that involved the entire epiphysis as well as some soft tissue components. Hence, our initial differential diagnosis did not include SBC. However, pathology confirmed a SBC. Thus, SBC should be considered in the diagnosis of cystic lesions despite the atypical imaging findings.