Optic Nerve Sheath Meningocele with Optic Disc Pit

Purpose: Optic nerve sheath meningocele is a very rare condition; if the optic nerve is pressed, visual function can deteriorate. We report a patient with optic nerve sheath meningocele treated with optic nerve sheath fenestration. Case summary: We report a 15-month-old male who visited the outpatient clinic due to an orbital tumor in the left eye found by accident. He had no proptosis or relative afferent pupillary defect, and fundus examination revealed a left optic disc pit. On fat-suppressed magnetic resonance imaging (MRI), there was a well-defined 13.5 × 12.7 mm cystic lesion located at the superotemporal aspect of the left optic nerve within the optic nerve sheath. The optic nerve was compressed and displaced inferomedially. Once the diagnosis had been confirmed as optic nerve sheath meningocele, optic nerve sheath fenestration was performed under general anesthesia to relieve optic nerve compression. The compressed left optic disc returned to normal after surgery and the size of the meningocele shrunk to 11.7 × 10.9 mm on MRI. However, it re-expanded to almost the same size as that preoperatively 10 months later. Conclusions: We report a case of optic nerve sheath meningocele with an optic disc pit treated with optic nerve sheath fenestration, which has not been reported previously in the Republic of Korea. Because the effect of optic nerve sheath fenestration could be temporary, it is necessary to conduct regular checkups given the possibility of deterioration of visual function. J Korean Ophthalmol Soc 2020;61(7):843-847