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Malignant transformation of an osteoblastoma of the skull: an exceptional occurrence. Case report.

What is apparently the first reported case of spontaneous malignant transformation of a benign osteoblastoma of the skull is described. The initial lesion was completely removed surgically and showed the histological features typical of a benign osteoblastoma. No radiotherapy was performed. Eleven years later the patient developed an osteosarcoma of the skull. Review of the literature showed that malignant transformation of benign osteoblastomas is extremely rare and could take place spontaneously. However, the risk of this occurring seems higher after inadequate initial treatment (curettage or partial excision). Follow-up monitoring of patients with osteoblastoma of the cranial vault is suggested.