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Previous Volume 347:1670-1676 November 21, 2002 Number 21 Next

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ABSTRACT

Background Fibrous dysplasia of bone frequently involves the anterior base of the cranium and results in encasement of the optic-nerve canals. It has been assumed that such encasement leads to constriction and eventual blindness. There is controversy about whether patients should be regularly monitored or whether they should undergo prophylactic decompression of the optic nerve. This question is of particular concern in patients with normal vision, since the risks associated with surgical decompression include blindness.

Methods We studied 38 patients with fibrous dysplasia of the lesser wing of the sphenoid bone. The patients underwent a detailed neuro-ophthalmologic examination and computed tomography of the face and skull, reformatted to measure the extent of involvement of the optic canal and the area of the canals. The results were compared with those of 38 age- and sex-matched controls.

Results Of the 38 patients, 15 were male and 23 female, and their mean age was 26 years. Twelve had polyostotic fibrous dysplasia, and 26 had the McCune–Albright syndrome. Sixty-seven optic canals were affected by fibrous dysplasia; in 49 of them (73 percent) there was complete encasement. The mean (±SD) areas of the right and left canals were 9.6±3.8 mm² and 9.9±3.6 mm², respectively, in the patients, as compared with 12.0±2.9 mm² and 11.9±2.7 mm² in the controls (P=0.009 for the comparison of the right areas and P=0.03 for the comparison of the left areas by the paired t-test). In all but two of the patients, the results of neuro-ophthalmologic examination were normal. In the two patients with monocular visual impairment, the areas of the optic canals were similar on the normal and abnormal sides.

Conclusions Encasement of the optic canal in fibrous dysplasia causes narrowing of the canal, but that in itself does not result in visual loss. Therefore, prophylactic decompression of the optic nerve does not appear to be indicated on the basis of the presence of fibrous dysplasia on diagnostic images alone, since it does not correlate with visual loss.

Source Information

From the Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research (J.S.L., P.G.R., M.T.C.), the National Eye Institute (E.F.), and the Department of Diagnostic Radiology, Warren G. Magnuson Clinical Center (J.A.B.), National Institutes of Health, Bethesda, Md.; the Division of Plastic Surgery, Georgetown University Medical Center, Washington, D.C. (C.R.D.); Biomedical Computer Research Institute, Philadelphia (H.K.); and the Department of Pediatric Orthopedic Surgery, Dana Children's Hospital, Tel Aviv, Israel (S.W.).

Address reprint requests to Dr. Lee at the Department of Oral and Maxillofacial Surgery, University of California–San Francisco, 521 Parnassus Ave., C-522, San Francisco, CA 94143-0440, or at jslee{at}itsa.ucsf.edu.

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