Infantile Aggressive Aneurysmal Bone Cyst of the Proximal Femur: A Rare Clinical Presentation.

Aneurysmal bone cysts (ABCs) are aggressive, osteolytic lesions usually seen in childhood and young adulthood. The patient's age, location, and behavior of the lesion in the bone may cause patients to present with different clinical findings. Appropriate treatment of these rare, aggressive bone lesions is essential for recurrence. This case report aims to present the diagnosis and treatment approach in the case of an infantile aggressive ABC and to present the long-term follow-up results. A 14-month-old baby boy was admitted to the clinic with the complaint of difficulty in walking after a fall. After evaluation with advanced imaging methods, a fluid-filled cystic lesion and pathological fracture were detected in the proximal femur. After surgical treatment of the lesion, which showed an aggressive course in the follow-up, the patient was able to give a whole load six months after surgery. Although the ABC was aggressive in this case, it was controlled with surgical treatment and long-term follow-up. It should be kept in mind that ABCs in children, especially in the proximal femur, may be aggressive and may require surgical treatment.