Optic nerve sheath meningoceles. Clinical and radiographic features in 13 cases with a review of the literature Thirteen patients with dilated intraorbital optic nerve sheaths with an expanded, patulous cerebrospinal fluid (CSF) space were studied with high-resolution computed tomography (CT) or magnetic resonance imaging (MRI). Eleven patients had bilateral findings. Headache or visual complaints, or both, were present in all patients. Signs of optic nerve dysfunction were present in eight patients. Three patients had visual acuity worse than 20/200. Cerebrospinal fluid pressure was mildly elevated in two patients. Three patients underwent a surgical procedure; visual acuity improved in one. The authors propose the term meningocele for this condition and suggest MRI with fat-suppression techniques and off-axis sagittal views as the radiographic procedure of choice. 