Congenital intradiploic arachnoid cyst presenting as painless proptosis.

A 12-year-old girl presented with several years of progressive painless proptosis and orbital fullness. On imaging, she was found to have marked expansion and remodeling centered in the right greater wing of the sphenoid bone with an adjacent middle cranial fossa arachnoid cyst. A clinical diagnosis of intradiploic arachnoid cyst was made. This entity was benign, and other ophthalmic and neurologic signs or symptoms were absent. Our patient was observed without surgical intervention. To our knowledge, this is the first such case reported in a child. Although this cyst has been described in the occipital and frontal bones, this is the first description of occurrence in the sphenoid bone.