Immediate Shrinkage of Optociliary Shunt Vessels after Fractionated External Beam Radiation for Meningioma of the Optic Nerve Sheath A.G. de Alba

SUMMARY: Fractionated stereotactic radiation has become the standard treatment of meningioma of the optic nerve sheath. The mechanism responsible for improvement in visual function is unclear, because neuroimaging after treatment usually shows no discernable change in tumor appearance. We report immediate regression of optociliary shunt vessels in a patient after radiation treatment of an optic nerve sheath meningioma. This observation indicates that radiation treatment can cause rapid reduction of optic nerve compression, even without appreciable reduction in the size of the meningioma. Collateral retinochoroidal vessels straddling the optic discborder, known as optociliary shunt vessels, are a classic finding in patients with optic nerve sheath meningioma.1 In healthy patients, retinal blood leaves the eye via the central retinal vein, which runs down the center of the optic nerve. The growth of a sheath meningioma causes gradual compres-sion of the central retinal vein, forcing blood to find alternative drainage routes. Retinochoroidal vessels, which are normally microscopic, become engorged by retinal blood that is shunted from the optic disc (opto) to the choroid (ciliary). Th