Definition A term of art referring to a small meningioma at the extreme posterior end of the orbit, just anterior to the optic foramen, which causes progressive visual loss without orbital signs. Such lesions may be undetectable by imaging (plain skull films, tomography, selective angiography with subtraction and magnification and CT), and only detected with exploratory craniotomy.
Comment Most of the literature on this term cite a 1977 paper by JO Susac et al. Without more recent data, it’s difficult to say whether such lesions would be “impossible” to identify non-invasively with high-resolution CT or current generation MRI.
Synonym Optic nerve sheath meningioma
Reference Susac, JO, Smith JL, Walsh FBArch Neurol. 1977;34(1):36-38.