Orbital Complications of Fibrous Dysplasia

Fibrous dysplasia (FD), an uncommon disorder of unknown origin, is characterized by the replacement of normal bone with a fibroblastic proliferation which contains irregular trabeculae of partially calcified osteoid. It comprises 2.5% of all bony tumors, and can be confined to one bone (monostotic), involve multiple bony sites (polyostotic), or be disseminated with abnormal cutaneous pigmentation and endocrine dysfunction in female patients (Albright's syndrome). 1.2 Approximately one half of bony lesions exhibit a mixed (or pagetoid) radiographic appearance, distinguished by irregular areas of alternating sclerosis and radiolucencies. The remaining lesions are either radiographically sclerotic (with dense bone) or lytic (with multiple, cystic radiolucent areas)." Except perhaps for Albright's syndrome, diagnosis of FD is seldom made on clinical, radiographic, or histologic criteria alone, but rather is based on consideration of all three factors. For instance, it is difficult to distinguish an en plaque meningioma from FD by radiographic means, but meningiomas most commonly occur in older adults, whereas FD usually appears in children.' Likewise, it can be difficult to differentiate FD from other benign bony tumors by histologic examination of a small biopsy. Twenty percent of patients with FD have craniofacial involvement, which tends to be unilateral and occurs more frequently in polyostotic cases.?" The dysplasia has a predilection for membranous bones, including (in order of frequency) the maxilla, mandible, frontal, and parietal bones. The characteristic presentation is a slowly progressive and asymptomatic bony swelling. Proptosis develops from encroachment of the orbit in thirty-five percent of patients with craniofacial FD and pain, diplopia, or epiphora can ensue." Impairment of vision occurs in most of these patients and results from