Aggressive sphenoid wing fibrous dysplasia with secondary aneurysmal bone cyst changes mimicking skull base malignancy

Background: Craniofacial fibrous dysplasia (FD) is a benign fibro-osseous disorder that may rarely demonstrate aggressive radiological features mimicking malignant skull base tumors. Secondary aneurysmal bone cyst (ABC) degeneration can further complicate the diagnostic assessment due to rapid expansion, cortical destruction, and heterogeneous imaging characteristics. Case Description: A 5-year-old girl presented with progressive left visual impairment and persistent headaches. Magnetic resonance imaging revealed an expansile osteolytic lesion involving the left sphenoid wing with heterogeneous enhancement, multiple cystic components, and radiological features concerning for malignancy. Surgical resection was performed through a temporal craniectomy approach. Histopathological examination demonstrated FD associated with secondary ABC changes without evidence of malignancy. Postoperative imaging confirmed complete resection, and the patient remained neurologically stable during follow-up. Conclusion: Aggressive craniofacial FD with secondary aneurysmal degeneration may closely simulate malignant skull base tumors, particularly in pediatric patients. Recognition of this rare presentation is essential to avoid overtreatment and highlights the critical role of histopathological confirmation in establishing the diagnosis.