The relationship between computed tomography measurement of the optic nerve sheath diameter and elevated intracranial pressure in non-trauma patients

Background: The early detection and treatment of raised intracranial pressure (ICP) is critical in the prevention of mortality and morbidity as a result of secondary ischemic brain injury. Measuring the optic nerve sheath diameter (ONSD) on computed tomography (CT) to predict raised ICP may be useful in cases where routine CT investigations of the brain are indicated and invasive ICP monitoring is not available, or a lumbar puncture (LP) is contraindicated. Objective: The purpose of this study was to determine if the ONSD can be measured on digital images obtained by routine CT investigations of the brain, to identify patients with non-traumatic causes of elevated ICP, and to provide the observer with a non-invasive, objective measurement to predict elevated ICP. Method: We conducted a cross-sectional, retrospective analysis of anonymised patient data, comparing the ONSD on CT imaging with the opening pressure manometry during LP on patients who presented with focal neurology or with a Glasgow coma scale score of less than 15. The study sample consisted of 67 patients, >= 18 years of age, treated at the emergency department of the Kimberly Hospital Complex from 01 March 2013 to 31 December 2014. Results: An ONSD measurement of >= 4.8 mm identified patients with an elevated ICP with a sensitivity of 92.9% and a specificity of 97.6%, using a 95% confidence interval. Raising the ONSD cut-off value to >= 5.0 mm decreased the sensitivity to 85.7% but increased the specificity to 100%, eliminating all patients with a normal ICP. Conclusion: The ONSD can be measured on digital images obtained by routine CT investigations of the brain to predict elevated ICP in non-trauma patients, >= 18 years of age, with acceptable sensitivity and specificity.