Normal Optic Nerve Sheath Diameter and its Relation with Orbital Diameter on 3T MRI: A Cross-sectional Study

• Main Authors: Anupama Chandrappa, Rajesh Raman, Rashmi, Radhika Devaramane, Sachin Shetty
• Format: Article
• Language: English
• Published: JCDR Research and Publications Pvt. Ltd. 2017-04-01
• Series: International Journal of Anatomy Radiology and Surgery
• Subjects: intracranial hypertension; mri brain; subarachnoid space
• Online Access: http://www.ijars.net/articles/PDF/2265/24843_CE[VSU]_F(GH)_PF1(VsuGH)_PFA(GH)_PF2(VsuGH).pdf
• ISSN: 2277-8543; 2455-6874

Introduction: The optic nerve is a direct continuation of the brain, surrounded by subarachnoid space. Measurement of the Optic Nerve Sheath Diameter (ONSD) provides indirect evidence of intracranial hypo or hypertension. This study provides age wise diameter of the optic nerve sheath from 0-100 years on T2 weighted MR images in a 3T MR scanner. The data serves as a baseline standard for comparison of ONSD in patients of various age groups. The regression equation obtained by the data provides the orbital diameter using ONSD. Aim: To establish age and sex wise reference norms for ONSD from 0-100 years. Materials and Methods: This was a retrospective crosssectional study of analysis of MR image data set of 500 consecutive MRI studies of the brain, with normal optic nerves. Out of them, 275 were males (55%) and 225 were females (45%). A total of 1000 optic nerves were measured (500 patients, both eyes). The study population was divided into 11 age groups of each decade of life from 0 to 100 years. Along with the ONSD, the orbital diameter was also measured. The data was tabulated age and sex wise, for both the eyes and analyzed. Results: Maximum right and left ONSD were 5.5 mm and 5.4 mm respectively. There was no statistically significant difference between the sides as well as genders. Significant difference was found between the mean orbital diameter of males and females, with that of males being greater than females bilaterally (p-value of 0.0001). In none of the subjects, the ONSD was above 5.5 mm. Conclusion: This study provides a baseline agewise ONSD and orbital diameter of general population. A regression equation for both the orbits is provided so that the orbital diameter can be estimated if ONSD is known and viceversa. The maximum ONSD in any age group is never above 5.5 mm. If higher ONSD is found, the patient should be thoroughly investigated for intracranial hypertension.