Correlations between optic nerve sheath diameters measured using computed tomography and elevated intracranial pressure levels

Abstract

BackgroundIncreased intracranial pressure (ICP) is commonly encountered in neurosurgery. Invasive external ventricular drainage is the gold standard ICP monitoring method. Higher ICPs enlarge the optic nerve sheath diameter (ONSD). Currently, few data describing correlations between ONSDs measured using computed tomography and ICPs. This manuscript describes a study that aimed to evaluate associations between the ICP and the ONSD measured using head CT, and to determine the ability of the ONSD to predict intracranial hypertension. ObjectivesWe aimed to study correlations between ONSDs and ICPs in patients who underwent ventricular shunting procedures, and to determine ONSD cutoff values that represent ICPs >15 mmHg and >20 mmHg, together with their sensitivities, specificities, negative predictive values (NPVs), and positive predictive values (PPVs). MethodsThe patients’ charts, operative notes, and brain computed tomography (CT) findings were reviewed retrospectively. The ONSDs were measured at 3 mm behind the globes on axial CT images from 102 patients who underwent ventricular shunting. Intraoperative ICP data were collected. ResultsA total of 102 patients were enrolled, comprising 93 (91.2%) without and 9 (8.8%) with traumatic brain injuries. Their mean age was 56.95 years (SD 17.01 years). The most common diagnoses were spontaneous intracerebral hemorrhages (ICH) with or without hydrocephalus (30 [29.4%]) and aneurysmal subarachnoid hemorrhages (SAH) (19 [18.6%]). The mean preoperative ONSD was 4.875 mm (SD 0.96 mm). The ONSD correlated significantly with the ICP levels (p < 0.001). An ONSD cutoff value of 5.125 mm predicted an ICP >15 mmHg (sensitivity: 94.7%; specificity: 90.6%; PPV: 85.7%; NPV: 96.7%). An ONSD cutoff value of 5.35 mm corresponded with an ICP >20 mmHg (sensitivity: 94.7%; specificity: 84.3%; PPV: 58.1 %; NPV: 98.6%). The ONSD decreased significantly to within the normal range (4.17 mm [standard deviation (SD) 0.60 mm]; p < 0.001) at 27 days (SD 14.70 days) postoperatively. ConclusionsCT-determined ONSDs correlated strongly with invasive ICP measurements. An ONSD of 5.35 mm, which corresponded with an ICP >20 mmHg, could become a noninvasive, alternative indicator for ICP level.