An aneurysmal bone cyst is an expanding osteolytic lesion consisting of blood-filled spaces of variable size separated by connective tissue containing trabeculae of bone or osteoid tissue and osteoclast giant cells.

The exact cause remains unknown. Genetic abnormalities such as chromosomal segment 7q, 16,p and 17 p11-13, especially to USP6 oncogene and CDH 11 promoter rearrangement are seen.

Secondary aneurysmal bone cysts are seen in giant cell tumors, osteoblastoma, chondroblastoma, non-ossifying fibroma, fibrous dysplasia, simple bone cyst, telangiectatic osteosarcoma, chondrosarcoma, and metastatic disease.

An aneurysmal bone cyst is most often affected between 5 and 20 years of age. There is no gender predilection or slightly more common in females. The most common sites affected are femur, tibia, spine, humerus, pelvis, and fibula. It usually involves the metaphyseal region and may occasionally cross the physis or may extend into the diaphysis. The usual symptoms are localized pain and swelling.

Often plain radiograph of the affected part is enough to make the diagnosis. However, computed tomography and magnetic resonance imaging are needed to evaluate the lesion. The radiographic finding is characterized by a radiolucent expanding periosteal blowout or balloon out the eccentric lesion. Multiple fluid levels are a feature of an aneurysmal bone cyst.

The expectant management is indicated only when the diagnosis has been made with confidence, the lesion is in such a location that does not entail any risk of fracture or further destruction.

Active treatment is often advocated for an aneurysmal bone cyst. Treatment options include-

Intralesional excision i.e. curettage and bone grafting or bone graft substitute or bone graft substitute with intralesional bisphosphonates.

Wide excision

Wide excision and reconstruction

No healing or recurrence is seen in 30 % of cases (14 to 60%).

Some lesions stabilize and/or regress.