Aneurysmal Bone Cyst (ABC)

Key Points:


Aneurysmal bone cyst (ABC) is a benign and non-neoplastic reactive bone lesion with multiple blood-filled cavities. Histologically, it is a cavernous vascular tumor that can range from a few millimeters to 1-2 cm in diameter with intralesional communicating cavitations. The cavity spaces are separated by fibrous septa made of spindle cells, inflammatory cells, and giant cells.


Primary ABCs occurs in 0.14 to 0.32 per 100,000 individuals. 75% of patients with this condition are older than 20 years. It occurs in males more often than females. Common sites of presentation include the calcaneus, femur, tibia, fibula, humerus, skull, and posterior elements of spine.

Clinical Findings:

Patients with this condition often present with pain and soft tissue swelling secondary to a pathological fracture.

Imaging Studies:

In an initial evaluation, radiographs show a radiolucent cystic lesion in the metaphyseal portion of bone. This lesion expands the surrounding cortical bone. The lesion is most often eccentric but can be central or subperiosteal.
CT scans can be utilized to better define the bony limits of the identified lesion. MRI with contrast will reveal internal septations with fluid-fluid levels. This finding on MRI could also be suggestive of telangiectatic osteosarcoma, giant cell tumor, secondary ABC, or fracture through a simple cyst.


After confirming the diagnosis histopathologically, treatment is pursued. Curettage and bone grafting with or without adjuvant therapy is the accepted method of treatment. Adjuvant therapy treats microscopic disease contamination. Curettage is done through either small fenestration, cortical window or complete saucerization. Cryotherapy and sclerotherapy are methods of adjuvant treatment used in conjunction to curettage to decrease recurrence rate.
Radionuclide ablation and arterial embolization are other potential methods to treat ABCs. However, these methods are not first line treatment. En bloc resection of ABCs is associated with the lowest rate of recurrence but is only indicated in expendable bone locations (eg, fibular, clavicle) and where performing this can be achieved without affecting cosmesis or function.


Younger age and open physes are known risk factors for ABC recurrence. Histologically, an ABC with a higher proportion of cellular tissue relative to the amount of osteoid and fibrillary content is a prognostic indicator of recurrence (Docquier, 2010). In addition, the presence of higher mitotic indices is a risk factor for an increased recurrence rate (Reuiter et al, 1977).
Malignant Transformation
Malignant transformation is rare and can occur with and without the use of adjuvants during primary treatment. Malignant transformation from ABC to fibroblastic osteosarcoma and telangiectatic osteosarcoma has been reported.

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