Background: Brain Computed Tomography (CT) is a fundamental diagnostic test to evaluate traumatic brain injury (TBI) patients. The optic nerve sheath (ONS) has been increasingly studied as an objective and practical parameter for estimating the existence of intracranial hypertension and for prognosis assessment. The aim of this study was to evaluate different measures in the optic nerve sheath as prognostic tools.

Methods: A retrospective cohort of patients with moderate and severe TBI admitted to the Intensive Care Unit (ICU) between April and September 2018. The following measurements of the ONS were performed on admission CT: diameter at 3mm (ONSD-3) and 10mm (ONSD-10) from the eyeball in the axial plane; ratio between the ONS-3 or the ONS-10 and the transverse diameter of the eyeball, resulting in NER-3 and NER-10; and cross-sectional area at 3mm (ONSA-3) and 10mm from the eyeball (ONSA-10). The association between measures and hospital mortality was investigated. A combined secondary outcome was defined as craniotomy within 5 days and/or death.

Results: 81 patients were included. Mean age was 36.3 +/- 15.8 years. 93% were men. 41% underwent craniotomy. Hospital mortality was 41%, while 72% had a combined outcome. None of the tomographic variables were significantly associated with in-hospital mortality. Craniotomy was a protective factor (p = 0.01). When considering the combined outcome, only ONSD-10 and NER-10 presented a significant association (p = 0.03 and p = 0.005, respectively). In the subgroup of non-operated patients, ONSD-10 and NER-10 demonstrated independent prognostic value for hospital mortality, with cut-off values of ONSD-10 > 4.3mm (AOR = 14.24, p = 0.03) and NER-10 > 0.19 (AOR = 24.87, p = 0.03).

Conclusion: The ONSD-10 and NER-10 measurements showed a better association with prognosis compared to measurements taken at 3mm, as well as other tomographic parameters for patients with moderate and severe TBI.