Optic nerve ultrasound for detecting intracranial hypertension

Introduction

The purpose of this study is to verify the reliability of optic nerve ultrasound (ONU) for detecting intracranial hypertension (IH). IH is a frequent and potentially fatal complication of severe head injury. Actually, intraventricular catheters represent the gold standard for ICP measurements. Unfortunately they present serious complications and relative contraindications like thrombocytopenia or coagulopathy. Computed tomography and transcranial Doppler (TCD) represent noninvasive methods to evaluate ICP but they present drawbacks. ONU has been recently suggested as a non-invasive tool to diagnose IH. Its reliability has been showed in patients with severe head injury or with intracranial hemorrhage [1, 2].

Methods

The study was conducted on 10 patients admitted to the neurointensive care unit for moderate/severe head injury in the period January to June 2009 (Group 1). Ten healthy subjects were enrolled as the control group (Group 2). Estimated ICP (eICP) was calculated with TCD using the equation proposed by Czosnyka and colleagues [3]. It was measured twice a day for 3 consecutive days. In the same sonographic session, the optic nerve sheath diameter (ONSD) was measured in the sagittal and transverse plane 3 mm behind the papilla, in both eyes.

Results

No significant differences have been found between groups regarding age and sex. The ONSD distribution is shown in Figure 1. ONSD, eICP and ICP values were significantly higher in Group 1 than in Group 2. Linear regression analysis identified a significant relationship between ONSD and ICP (r = 0.588). By calculating the receiver operating characteristic curve, an ONSD value of 5.35 mm resulted as the optimal cut-off point with a sensitivity of 95.1% and a specificity of 96.2%.

Figure 1

ONSD distribution in patients with ICP less than and more than 20 mmHg.

Conclusions

ONSD measurements correlated with invasive and noninvasive (TCD) measurements of ICP. It is a useful, non-invasive bedside tool to diagnose IH. It is safe, easy to perform and can rapidly give reproducible information on patients' ICP.