Optic Nerve Sheath Diameter Measured Using Magnetic Resonance Imaging and Factors That Influence Results in Healthy Chinese Adults: A Cross-Sectional Study
The measurement of intracranial pressure (ICP) is a critical aspect of managing neurosurgical and neurological disorders. Elevated ICP is associated with severe outcomes, including brain herniation and death. While invasive methods such as intraparenchymal or intraventricular monitoring remain the gold standard for ICP measurement, they are not always feasible due to the lack of neurosurgeons, contraindications like blood coagulation disorders, and complications such as infection and hemorrhage. Consequently, there is a growing need for accurate non-invasive methods to estimate ICP in clinical practice. One such method involves measuring the optic nerve sheath diameter (ONSD), which has been shown to have a linear relationship with ICP. This has led to increased interest in ONSD measurement techniques, particularly non-invasive methods like ultrasound and magnetic resonance imaging (MRI).
MRI, with its high spatial resolution and clear delineation of orbital structures, has emerged as a reliable tool for measuring ONSD. However, the lack of established normative values for ONSD measured by MRI poses challenges in defining diagnostic criteria for raised ICP. Previous studies have primarily focused on Caucasian populations and included only small numbers of healthy subjects. This study aimed to establish normative values for ONSD using MRI in a large cohort of healthy Chinese adults and to evaluate the relationship between ONSD and demographic, clinical, and anatomical parameters.
The study was approved by the Ethics Committee of the University of Science and Technology of China (USTC). Due to its retrospective nature, informed consent was not required. The study reviewed brain MRI scans of 428 participants who underwent comprehensive physical examinations at the First Affiliated Hospital of USTC between July 2017 and November 2019. Inclusion criteria were age 18 or older and no history of abnormal ICP. Exclusion criteria included a history of ophthalmological or neurological diseases, intracranial lesions affecting ICP, and poor imaging quality due to movement or metal artifacts. After exclusions, 413 individuals were included in the study.
Demographic and physiological data collected included age, sex, weight, height, body mass index (BMI), and mean arterial blood pressure (MABP). MRI was performed using a GE Discovery MR750 3.0T scanner. Participants were instructed to keep their eyes closed with minimal movement during scanning. Axial images were collected parallel to the horizontal plane connecting the anterior and posterior commissures, covering the entire brain. ONSD and eyeball transverse diameter (ETD) were measured using time-of-flight magnetic resonance angiography (TOF-MRA) with specific imaging parameters.
Two experienced radiologists independently assessed the MRI data using an image archive and communication system. ONSD was measured 3 mm behind the eye along an axis perpendicular to the optic nerve, with the retrobulbar area enlarged by 10 times. ETD was measured as the transverse diameter of the eyeball. Four images showing the maximum ONSD and ETD for each eye were selected, and each eye was measured three times. The average of these measurements was used as the final value.
Statistical analysis was performed using SPSS version 17.0. Continuous variables were presented as mean ± standard deviation (SD) and median (interquartile range), while categorical variables were presented as frequencies and percentages. Simple linear regression and multiple regression analyses were conducted to determine factors related to ONSD. Variables with a P value <0.05 in simple linear regression were included in the multiple linear regression model. Two independent sample t-tests were used to assess the effect of gender on ONSD and ETD. A P value <0.05 was considered significant.
The study included 413 healthy subjects aged 21 to 88 years (mean age 58.0 ± 16.0 years), with 227 (55%) being male. ONSD values for both eyes showed no significant difference. Simple linear regression analysis revealed that ONSD was correlated with sex and ETD. Multiple regression analysis confirmed these associations, showing that ONSD was significantly associated with sex and ETD. When participants were divided by gender, males had significantly larger ONSD and ETD values than females.
The mean ONSD and ONSD/ETD ratio measured by MRI were 4.76 ± 0.43 mm (95% confidence interval [CI], 4.72–4.80 mm) and 0.22 ± 0.02 (95% CI, 0.21–0.22), respectively. These values were larger than those obtained using ultrasound, likely due to MRI’s superior spatial resolution and ability to clearly delineate orbital structures. Previous studies have reported ONSD values ranging from 3 to 5 mm in healthy participants, with European and American populations showing larger values (5.08–5.72 mm) compared to Asian populations (4.71–5.1 mm). This suggests that racial and genetic differences may influence ONSD measurements.
The study found that ONSD was correlated with ETD and sex but not with age, weight, height, BMI, or MABP. The significant association between sex and ONSD, with males having larger values than females, aligns with previous research. This gender difference may be due to variations in nerve fiber density between sexes. The study’s large sample size and balanced gender distribution allowed for the detection of these differences, which may have been overlooked in smaller studies.
In conclusion, this study established normative values for ONSD and the ONSD/ETD ratio measured by MRI in healthy Chinese adults. The mean ONSD was 4.76 mm (95% CI, 4.72–4.80 mm), and the ONSD/ETD ratio was 0.22 (95% CI, 0.21–0.22). ONSD was significantly associated with ETD and sex, with males having larger values than females. These findings suggest that separate reference ranges may be required for men and women when using ONSD as a diagnostic indicator of raised ICP.
doi.org/10.1097/CM9.0000000000001353
Was this helpful?
0 / 0