Giant aneurysmal bone cyst mimicking malignant tumor

Aneurysmal bone cyst (ABC) is a bone tumor which occurs mostly in young adults. Despite its benign character, it may sometimes locally turn malignant and can reach a significant size. Therefore, it is not uncommon for this disease to become similar to a malignant, destructive process and to be difficult to diagnose. We present a case of a 12-year-old girl with a rapidly growing mass in the region of the left hip joint. Imaging (X-ray, MRI, CT) showed a growing lesion in the proximal part of the femur that damaged the cortical layer of the bone. This suggested a presence of rhabdomyosarcoma. The lesion was removed surgically and the bone defects were filled with grafts. Two months after the surgery the patient reported pain in the area of the right groin and left knee. X-ray showed bone lesions in the right pubic bone and the left femoral bone. The biopsy showed no pathological lesions. One year after the surgery, lesions in the X-ray image of the right pubic bone and left femoral bone remitted spontaneously. Ten years after the diagnosis of the aneurysmal bone cyst no recurrence of the disease or other ailments was observed.