Monostotic fibrous dysplasia of the sphenoid sinus: a serendipitous finding on a bone scan.

A 22-year-old woman had a Tc-99m MDP whole-body scan for low back pain. A focal area of increased activity was seen in the skull base in the region of the sella turcica. A computed tomographic examination showed ground-glass opacification of the sphenoid sinus and bony sclerosis along its walls, characteristic of fibrous dysplasia. Monostotic fibrous dysplasia, the more common form compared with the polyostotic variety, occurs in 70% to 80% of all patients with fibrous dysplasia. Monostotic lesions usually involve the ribs, femur, tibia, cranium, maxilla, and mandible. The frontal and sphenoid bones are the cranial bones most commonly involved.