Effect of cervical sympathetic block on optic nerve sheath diameter measured by ultrasonography

Optic nerve sheath diameter (ONSD) measurement using ocular ultrasonography was introduced as a non-invasive technique to assess intracranial pressure. We investigated changes in ONSD after cervical sympathetic block (CSB). Ultrasound-guided CSB was performed with a lateral approach at the C6 level in 35 patients. ONSD was measured before CSB and after checking for Horner's syndrome 15 minutes after CSB. The mean ONSD was significantly higher after CSB than before (5.15 ± 0.38 mm vs. 4.75 ± 0.32 mm, p < 0.001). A comparison of ONSDs between the blocked and non-blocked sides revealed that these values did not differ significantly between sides at baseline and after CSB. On the basis of these preliminary data, CSB caused an increase in ONSD in patients without intracranial pathology or neurologic disorders. Further larger and controlled studies of the effect of CSB on intracranial pressure in humans are needed to confirm our findings.