[Optic nerve subarachnoid space expansion in MR imaging: a etiology study].

Objective To investigate spectrum of causes in optic nerve subarachnoid space (ONSS) expansion by using Magnetic Resonance Imaging (MRI). Methods A retrospective study. Twenty-six patients (46 eyes) with ONSS expansion and 20 healthy adults (40 eyes) were recruited in Neuro-ophthalmology Department of Chinese PLA General Hospital from January, 2014 to December, 2015. The diameters were measured on the optic nerve (OND) and optic nerve sheath (ONSD) 2.4 mm behind the globe. ONSS was calculated by the formula of (ONSD-OND)/2. All participants were under went ophthalmologic examinations. The patients' clinical features, MRI and final diagnosis were analyzed. Qualitative data were compared between groups by using chi square test and quantitative data were compared by independent sample t test. Results There was no statistically significant difference between ONSS group and control group with age, BMI and mean arterial blood pressure (P>0.05). Larger space was found in ONSS group with mean±standard deviation (SD) of (1.9±0.4) mm comparing to the control group with (1.2±0. 2) mm (t=2.879, P<0.01). Bilateral ONSS expansion were found in 20 patients, 15 patients (75%) with cerebral venous sinus thrombosis (CVST), 2 patients (10%) with neurosyphilis, 2 patients (10%) with peri-neuritis and 1 patient (5%) with hydrocephalus. Unilateral ONSS expansion were seen in 6 patients, 4 patients (66.7%) with compressive lesson on anterior visual pathway, 1 patient (16.7%) with fungal infection and 1 patient (16.7%) with peri-neuritis. Conclusions The CVST patients more frequently presented bilateral ONSS expansion. Unilateral ONSS expansion may indicate compressive lesions located on the anterior visual pathway. (Chin J Ophthalmol, 2016, 52: 911-917) Key words: Subarachnoid space; Optic nerve diseases; Magnetic resonance imaging