Correlation between Optic Nerve Sheath Diameter and Marshall Scale in Acute Traumatic Brain Injury

Abstract

Background: Imaging plays integral role in the evaluation of patients with acute traumatic brain injury (TBI), with computerized tomography (CT) being the modality of the choice and the most commonly utilized imaging tool. One of the important determinants of TBI severity is raised intracranial pressure (ICP). Optic nerve sheath diameter (ONSD) was considered as a reliable indirect surrogate for the raised ICP, however, studies assessing role of CT-derived ONSD in evaluation of patients with raised ICP or brain injury are limited. Aim of the study: To assess the correlation between ONSD measured by CT scan and the severity of TBI according to Marshall scale. Patients and methods: A cross-sectional analytic study was conducted on 60 adult patients (52 males, 8 females) presented with acute TBI and referred for brain CT examination. After initial general evaluation of brain CT images, the score of TBI was assessed according to Marshal's scale (I to VI). The transverse ONSD was manually measured on axial CT image at 3 mm distance behind eye globe. The correlation between the grade of TBI and ONSD was subjected to statistical analysis. The study was approved by the Institutional Ethical Review Committee. Results: The means of all, right-sided and left-sided ONSD were 4.695 mm, 4.606 mm and 4.785 mm respectively. There was positive, linear and statistically significant correlation (p value <0.001, r = 0.662) between the mean of ONSD measured by CT scan and Marshall score. When the ONSD measurements of the right and left sides were analyzed separately, the correlation was also significant and positive (r= 0.504 for the right side, r = 0.699 for the left side with p value <0.001 for both). ONSD showed weakly negative and statistically not significant correlation (p value= 0.571, r = - 0.075) with the duration between onset of the trauma and time of CT examination. There was no significant difference between mean ONSD measurements when correlated with the laterality of TBI, age or gender (p values 0.392 0.328 and 0.462 respectively). Conclusion: ONSD measured on brain CT scan is positively correlated with the severity of TBI as assessed by Marshall scale. Because Marshall scale has prognostic implication, ONSD may also have a prognostic value during assessment of patients with TBI.