Correlation of optic nerve sheath diameter with directly measured intracranial pressure in Korean adults using bedside ultrasonography

Abstract

Objectives: The correlation of optic nerve sheath diameter (ONSD) as seen on ultrasonography (US) and directly measured intracranial pressure (ICP) has been well described. Nevertheless, differences in ethnicity and type of ICP monitor used are obstacles to the interpretation. Therefore, we investigated the direct correlation between ONSD and ventricular ICP and defined an optimal cut-off point for identifying increased ICP (IICP) in Korean adults with brain lesions.

Methods: This prospective study included patients who required an external ventricular drainage (EVD) catheter for ICP control. IICP was defined as an opening pressure over 20 mmHg. ONSD was measured using a 13 MHz US probe before the procedure. Linear regression analysis and receiver operator characteristic (ROC) curve were used to assess the association between ONSD and ICP. Optimal cut-off value for identifying IICP was defined.

Results: A total of 62 patients who underwent ONSD measurement with simultaneous EVD catheter placement were enrolled in this study. Thirty-two patients (51.6%) were found to have IICP. ONSD in patients with IICP (5.80 ± 0.45 mm) was significantly higher than in those without IICP (5.30 ± 0.61 mm) (P < 0.01). The IICP group showed more significant linear correlation with ONSD (r = 0.57, P < 0.01) compared to the non-IICP group (r = 0.42, P = 0.02). ONSD > 5.6 mm disclosed a sensitivity of 93.75% and a specificity of 86.67% for identifying IICP.

Conclusion: ONSD as seen on bedside US correlated well with directly measured ICP in Korean adults with brain lesions. The optimal cut-off point of ONSD for detecting IICP was 5.6 mm.

Fig 1

(A): ONSD in groups without IICP and with IICP. The bar represents the median value and the 25th to 75th percentiles. ONSD in patients with IICP (5.80 mm, range 4.3–6.7 mm) is significantly higher than that in those without IICP (5.3 mm, range 4.0–6.2 mm) (P < 0.001). (B): The area under the receiver operator characteristic curve is 0.936. ONSD > 5.6 mm yielded a sensitivity of 93.75% (95% CI: 79.2%–99.2%) and a specificity of 86.67% (95% CI: 69.3%–96.2%).

Fig 2. Scatterplot relating optic nerve sheath diameter (ONSD) and intracranial pressure (ICP) according to the presence of increased intracranial pressure (IICP).

The linear prediction from regression is shown as solid or dotted line.

Fig 3

(A, B): A 65-year-old man presented with sudden-onset altered mentality caused by acute IVH and hydrocephalus. US ONSD was measured as 5.7 mm and an EVD was placed in the right lateral ventricle with an opening pressure of 22 mmHg. (C, D): Three hours later, the patient’s ICP surged to 40 mmHg with an ONSD of 6.4 mm due to rebleeding of the right PICA aneurysm. Emergency coil embolization of the right PICA aneurysm was performed and another EVD was inserted in the left lateral ventricle. (E, F): Brain CT scans taken 3 weeks after the operation showed a substantial improvement of hydrocephalus and IVH with an ICP of 10 mmHg and an ONSD of 5.4 mm.