The impossible meningioma.

Experience in three cases has shown that a small meningioma in the extreme posterior portion of the orbit just anterior to the optic foramen may occur with progressive visual loss in the absence of orbital signs. Such lesions cannot be detected by plain skull roentgenography, polytomography, or selective angiography with subtraction and magnification. In one patient, even computerized axial tomography gave normal results, and the meningioma went undetected until exploratory craniotomy.