Fibrous dysplasia of both alae of the sacrum

A case of monostotic fibrous dysplasia involving both alae of the sacrum is reported. Only 2 cases of monostotic sacral involvement were published previously. The lesion was detected in a 42-year-old man suffering from lumbosacral pain after minimal trauma. Radiographic studies revealed cystic images on both alae of the sacrum, with internal condensations and some liquid contents. A trephine biopsy did not produce enough diagnostic data, and a posterior surgical approach was elected. Curettage and refilling with allograft were performed. The pathologic anatomy study diagnosed a fibrous dysplasia. Two years after surgery, the patient was asymptomatic.