Ultrasonographic evaluation of optic nerve sheath diameter in severe traumatic brain injury patients: a comparison with intraparenchymal pressure monitoring

Objective: Increased intracranial pressure (ICP) can worsen the clinical condition of traumatic brain injury (TBI) patients. One non-invasive and bedside-performed technique to estimate ICP is ultrasonographic measurement of optic nerve sheath diameter (ONSD). This study aimed to analyze ONSD and correlate it with ICP values obtained by intraparenchymal monitoring to establish the ONSD threshold value for elevated ICP and reference range of ONSD in severe TBI patients. Methods: Forty severe TBI patients were included. Ultrasonographic measurement of ONSD was performed and compared with intraparenchymal ICP monitoring to assess their association and determine the ONSD threshold value. Exclusion criteria included individuals under eighteen years old, penetrating TBI, or direct ocular trauma. Results: Fifty-three ONSD measurements were conducted in all patients. The mean ONSD value in the group with intracranial pressure < 20 mmHg was 5.4 mm ± 1.0, while in the group with intracranial pressure ≥ 20 mmHg, it was 6.4 mm ± 0.7 (p = 0.0026). A positive and statistically significant correlation, albeit weak (r = 0.33), was observed between ultrasonographic measurement of ONSD and intraparenchymal ICP monitoring. The statistical analysis of the ROC curve identified the best cut-off as 6.18 mm, with 77.8% sensitivity and 81.8% specificity. Conclusion: Our results reveal a positive, albeit weak, correlation between ultrasonographic measurement of ONSD and intraparenchymal ICP monitoring, with an ONSD threshold value of 6.18 mm. Achieving only 77.8% sensitivity and considering the substantial variability between ONSD measurements (standard deviation at 1.0) might limit the reliability of ICP assessment based solely on ONSD measurements.