# Temporal Evolution of Optic Nerve Sheath Diameter/Eyeball Ratio on CT and MRI for Neurological Prognostication After Cardiac Arrest

## TL;DR

This study examines how optic nerve sheath measurements on MRI and CT scans can predict neurological outcomes in cardiac arrest survivors.

## Contribution

The study evaluates the prognostic value of optic nerve sheath diameter and its ratio to eyeball diameter measured at specific time points after cardiac arrest.

## Key findings

- Post-TTM MRI measurements of ONSD and ONSD/ETD were significantly higher in patients with poor neurological outcomes.
- Prognostic performance of ONSD and ONSD/ETD was modest (AUC 0.67 and 0.65) and lower than early measurements.
- CT showed higher intra-rater reliability for ONSD and ETD measurements compared to MRI.

## Abstract

Background: Optic nerve sheath diameter (ONSD) and its ratio to eyeball transverse diameter (ETD; ONSD/ETD) are potential markers for elevated intracranial pressure in comatose survivors of out-of-hospital cardiac arrest (OHCA). However, their prognostic accuracy remains uncertain. We compared their predictive value via compted tomography (CT)and magnetic resonance imaging (MRI) before and after targeted temperature management (TTM) in OHCA survivors. Methods: This retrospective study included adult comatose OHCA survivors who underwent TTM and serial brain imaging. ONSD and ONSD/ETD ratios were measured on brain CT and MRI at two predefined time-points: within 6 h (pre-TTM) and at 72–96 h (post-TTM) after return of spontaneous circulation. Intra-rater reliability was assessed using intraclass correlation coefficients (ICC). Poor neurological outcome was defined as a Cerebral Performance Category score of 3–5 at 6 months. Prognostic performance was evaluated using area under the receiver operating characteristic curve (AUC). Results: Among 136 patients, 78 (57%) had poor neurological outcomes. Only ONSD (5.12 vs. 5.37 mm) and ONSD/ETD ratio (0.22 vs. 0.23) measured on post-TTM MRI were significantly higher in the poor outcome group. These results depicted modest predictive performance (AUC, 0.67 and 0.65, respectively), whereas all CT-based and early MRI measurements had AUC < 0.60. Intra-rater reliability for ONSD and ETD was higher on CT (ICC: up to 0.93) than on MRI (ICC: 0.73–0.80). Conclusions: Delayed MRI-based ONSD and ONSD/ETD showed statistically significant but modest prognostic value, with limited clinical applicability as a stand-alone tool. These findings underscore the relevance of measurement timing, supporting ONSD as an adjunctive, rather than definitive, tool in multimodal prognostication.