S16-12 SESSION 16: PLANNING/IMAGING – PART II LONG-TERM FOLLOW-UP SHOWS STABILIZATION OF VISION AND OPTIC CANAL CALIBER IN FIBROUS DYSPLASIA

Abstract

Introduction: Fibrous dysplasia (FD) is an expansile bone disorder that frequently involves the anterior cranial base and may encase the optic canal. Some have assumed that radiographic encasement results in gradual constriction, progressive optic neuropathy (ON), and eventual blindness. Thus, prophylactic decompression surgery has been recommended based on radiographic evidence of canal narrowing despite risks of surgery. Lee et al (2002) showed no correlation between canal constriction and visual disturbances. However, the long-term sequalae of optic nerve FD encasement is unknown. The aim of this study is to correlate long-term vision and optic canal caliber in patients with FD encasement. Methods: Patients enrolled in a FD natural history study (1998–2014) were screened. Patients with FD of the sphenoid, serial neuro-ophthalmologic exams (NOE) and head CTs, no history of decompression surgery or confounding ophthalmologic diagnoses were included (N=63). 5 NOE variables were evaluated: visual acuity, visual fields, color vision, contrast vision, and fundoscopic exam. ON was defined as abnormal visual fields or abnormal results on 2 of the other 4 tests. Cross-sectional area of the canal on multiplanar-reconstructed CTs was obtained. Generalized mixed model analysis evaluated changes in optic canal area over time, and the effects of endocrinopathies, skeletal disease burden, and bisphosphonates were examined. Results: Baseline mean age: 19 years (4–60); mean follow-up: 4.9 years (1–13.5). At baseline, 6 subjects had clinically significant ON; 2 worsened with time. No patients developed new ON. Optic canal area decreased through puberty and stabilized in adulthood (Fig.1). Patients with ON exhibited a faster rate of canal narrowing than those with normal vision (-0.37 vs. -0.12 mm2/year), p<0.05. There was no difference in optic canal area between groups. Subjects with precocious puberty and higher disease burden had narrower canals (p<0.05). Other variables had insignificant effects. Conclusion: This work extends our previous cross-sectional study and establishes that vision remains stable over time despite narrowing of the optic canal. In patients with ON, narrowing of the optic canal occurs at a faster rate. Yet, there was no difference in overall canal area between those with ON and normal vision, suggesting the mechanism of injury relates to pathologic rate of change in optic canal caliber. Since the greatest change in optic canal area occurs through puberty, patients should be monitored closely at that time. Prophylactic decompression remains contraindicated without evidence of rapid change in visual function.