Surface Aneurysmal Bone Cyst

We present a case of a surface aneurysmal bone cyst in a 19-year-old boy. Plain radiograph showed an osteolytic lesion with sclerotic margin and interrupted lamellar periosteal reaction at the posterolateral aspect of the diaphysis of the left proximal femur. MRI confirmed a bony lesion containing a fluid-fluid level (FFL) on T2-WI. Bone marrow oedema was seen within the femoral diaphysis and the soft tissue changes adjacent to the femoral cortex were enhancing. Because of the aggressive appearance on imaging, the patient underwent a biopsy and the final diagnosis of a subperiosteal aneurysmal bone cyst (ABC) was made. The patient was treated with curettage of the lesion.