Fibrous dysplasia of the orbital bones.

A NUMBER of bone diseases may affect the orbital bones decreasing the orbital volume and narrowing the optic canal, giving rise to unilateral exophthalmos and usually optic atrophy, simulating clinically an orbital tumour. Among such diseases are osteitis deformans (Paget, 1876); leontiasis ossea (Virchow, 1896); osteopetrosis (Albers-Schonberg, 1904), and the generalized and localized osteitis fibrosa cystica described by von Recklinghausen. Albright, Butler, Hampton, and Smith (1937) classified the localized osteitis fibrosa lesions as solitary and disseminated according to the number of bones affected. For these two forms, Lichtenstein (1938) introduced the terms monostotic and polyostotic fibrous dysplasia of bone. Fibrous dysplasia of bone differs from generalized osteitis fibrosa cystica. Clinically it appears about the age of 10 years, is usually attributed to trauma, and becomes stationary after a limited period of active bony changes in a limited area. The aetiology of the disease is unknown, but it is probably a developmental mesodermal disorder. The blood calcium, phosphorus, and plasma phosphatase are normal. There is no hyperparathyroidism. Histopathologically the disease is characterized by the way in which the medullary cavity of the affected bones is filled by fibrous tissue in which spicules of calcified bone may be developed and small islands of hyaline cartilage may sometimes appear. As a consequence, there is widening of the affected bones with thinning of their cortex and replacement of cancellous bone and marrow by solid fibrous tissue (Duke-Elder, 1952). Cyst formation may be present but osteoclastoma has not been recorded. X-ray examination shows the affected bone to be expanded and trabeculated; some areas are thick while others are porous. This picture differs from that of osteitis deformans, leontiasis ossea, osteopetrosis, metastasis, and osteogenic sarcoma of orbital bones, orbital osteoma, and sphenoidal ridge meningeoma. Polyostotic fibrous bone dysplasia, with sexual precocity (mostly in females), and patchy cutaneous pigmentation constitute Albright's syndrome. Few cases of fibrous dysplasia of the orbital bones are recorded in the literature, so that the description of a new case is still of interest.