Case reports: malignant transformation of aneurysmal bone cysts.

An aneurysmal bone cyst is an uncommon benign primary bone tumor. Careful intralesional curettage through a wide cortical window in addition to cauterization with or without adjuvant therapy (phenol or hydrogen peroxide) and bone grafting or cementation is the preferred surgical treatment. Adjuvant or primary radiation of an aneurysmal bone cyst rarely is used because of its association with malignant transformation of the lesion. Several cases of late malignant transformation of primary aneurysmal bone cysts without adjuvant radiation have been reported. We provide additional documentation of two primary aneurysmal bone cysts treated surgically with careful intralesional curettage through a wide cortical window and allograft bone grafting without adjuvant radiation. At 5.5 years and 12 years after treatment, a telangiectatic osteosarcoma and a fibroblastic osteosarcoma, respectively, were identified in the site of the original lesions. Not only should aneurysmal bone cysts be evaluated carefully through histologic examination at presentation, patients also should be counseled regarding possible recurrence and the need for routine followups, especially if symptoms change.