Magnetic Resonance-Based Assessment of Optic Nerve Sheath Diameter: A Prospective Observational Cohort Study on Inter- and Intra-Rater Agreement.

Background: The measurement of optic nerve sheath diameter (ONSD) as a non-invasive method of estimating intracranial pressure has been widely reported in the literature. However, few studies have evaluated the accuracy of magnetic resonance imaging (MRI) in assessing ONSD measurements, although it is considered a very reliable method, it is not easily repeatable, expensive and is not readily available bedside. Herein, an assessment of the intra- and inter-rater reliability of ONSD assessment using MRI was conducted.

Methods: A consecutive, prospective cohort of patients with suspected idiopathic normal-pressure hydrocephalus was analyzed. ONSD MRI measurements of the transverse and sagittal diameters at a distance of 3 mm behind the papilla were evaluated twice each by two expert neuroradiologists. The correlations between MRI examiners were calculated using the concordance correlation coefficient (CCC).

Results: Fifty patients were included in the study. ONSD MRI average measurements were substantially higher than clinically expected (>5 mm). Considering intra-rater concordance, only one of the two neuroradiologists achieved an excellent score at CCC. Only a moderate inter-observer CCC for MRI assessment was found at all diameters.

Conclusions: The use of a widespread MRI sequence (3D T1) to measure ONSD is not an accurate method since it may overestimate measurements and is dependent upon an operator.