Both MAS and isolated FD are sporadic noninherited genetic disorders caused by postzygotic mutations of GNAS1 gene encoding α subunit of stimulatory G protein (12,13). The phenotype from postzygotic single-cell GNAS1 mutation is variable, ranging from a constellation of multisystemic abnormalities to single or multiple FD lesions confined to the skeleton system (14–16). Whether the disease is generalized or localized depends on when the mutation occurs during embryogenesis (12).
Both acute and chronic visual impairment have been well documented in the literature in FD/MAS patients. Michael et al (3) noted that most reported cases of vision loss in FD are because of mass lesions, including cystic FD, mucocele, and aneurysmal bone cyst.
Progressive optic canal narrowing has long been considered a major cause of chronic optic neuropathy in craniofacial FD/MAS patients. This has led to prophylactic optic canal decompression (6,7). However, in a large cross-sectional analysis of a case–control cohort, Lee et al (8) showed that narrowing of the optic canal in craniofacial FD was not associated with visual loss. In this study, the majority of patients did not develop optic neuropathy even with severely narrowed optic canals. In addition, reports (9,10) of both prophylactic and interventional optic canal decompression with long-term follow-up do not demonstrate efficacy of this surgical procedure. Currently, optic canal decompression is only recommended for FD patients with acute or progressive visual impairment (3,9,17).
FD/MAS patients were not screened for pituitary tumor in previous studies. However, in our patients, the results of VF testing and neuroimaging indicated optic chiasm compression, and they all underwent transsphenoidal tumor resection with improvement of VFs. We conclude that chiasmal compression was a contributing factor to visual impairment. In addition, pituitary adenoma also might explain the association of GH excess documented in previous studies of patients with MAS (9,14).
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