Correlation Between Optic Nerve Sheath Diameter at Initial Head CT and the Rotterdam CT Score

Abstract

Introduction Intracranial findings on imaging have long been used in assessing the severity of traumatic brain injury (TBI); the Rotterdam CT scoring (RCTS) is a more recent tool. Estimating the optic nerve sheath diameter (ONSD) at computed tomography (CT) can be another valuable predictor of the severity of the injury, especially as both ONSD and the RCTS are proven to be independent predictors of raised intracranial pressure (ICP). The study objective was to determine the correlation between ONSD at initial head CT and RCTS. Material and methods We observed 40 consecutive confirmed TBI cases at their initial head CT examinations in the emergency department for ONSD and the presence of other intracranial findings necessary to derive RCTS. The data were prospectively collected and analyzed, with statistical significance set at p ≤0.05 at 95% CI. Results The mean ONSD positively correlated with the Rotterdam CT score (r=0.368, p=0.019). A cut-off value of 6.83 mm was extrapolated from the receiver operator characteristic (ROC) curve as the mean binocular ONSD that best predicted severe RCTS (≥4) (sensitivity: 73.3%, specificity: 80%, positive predictive value: 68.7%, negative predictive value: 83.3%). The area under the curve (AUC) was 0.780 (p=0.003). Binary logistic regression analysis revealed an odd ratio (OR) of 11.000 (95% CI: 2.438-49.627; p=0.002). Conclusion TBI patients with high RCTS have wide mean binocular ONSD. Those with average binocular ONSD above the cut-off value are likelier to have severe TBI. With the documented good correlation, ONSD may become very useful in informing the clinical decision for sequential CT scans in TBI patients and, therefore, reducing the cumulative radiation burden from needless exposures. Furthermore, the non-invasive nature of its assessment will have more clinical relevance in resource-limited settings, where the skills and equipment for ICP monitoring are either not readily available or too expensive to be used routinely.

Keywords: midline shift; neuro-critical care; noninvasive intracranial pressure monitoring; optic nerve sheath diameter; rotterdam computed tomography score; severity; traumatic brain injury.

Figure 1. Rotterdam CT score of the cases.

Figure 2. Non-enhanced CT images of the head.

(a) There is an extensive crescentic lesion in the right parietal convexity, with a fluid-fluid (haematocrit) level. It has caused marked effacement of the regional sulci and the anterior horn of the right lateral ventricle, with significant contralateral shift (>5 mm) of the midline brain structures. (b) At the level of the orbit, there is increased ONSD (6.41 mm) taken 3 mm behind the globe. Only the right intraconal ONSD complex is fully shown in this section. ONSD: optic nerve sheath diameter.

Figure 3. Receiver operator characteristic curve: ONSD as a predictor of RCTS.

ONSD: optic nerve sheath diameter, RCTS: Rotterdam CT score.