Agreement Between Computed Tomography And Magnetic Resonance Imaging In Measuring Optic Nerve Sheath Diameter

BACKGROUND: Neuroimaging is increasingly used as a non-invasive method to assess raised intracranial pressure (ICP). Optic nerve sheath diameter (ONSD) measurement using brain magnetic resonance imaging (MRI) has been shown to correlate well with invasively measured ICP, however little research has been conducted on the ONSD measurement using computerized tomography (CT) in correlation with ICP. This study was done to investigate whether CT scan can reliably replace MRI in measuring ONSD.

METHOD: A cross-sectional comparative study was conducted on 50 adult patients (29 females and 21 males), who underwent both CT and MRI of the brain along 10-month period. Using the brain axial section, the transverse ONSD was measured at 3 mm behind the globe in both modalities. Agreement between CT and MRI readings was assessed using intraclass correlation (ICC) and Kappa method.

RESULTS: There was a strongly positive and statistically significant correlation between ONSD measurement using CT scan and MRI (p value <0.001). There was almost perfect agreement between CT scan and MRI in measuring ONSD (ICC=0.987 and Kappa =0.837). Similar agreement was obtained when cases stratified into normal (≤ 5mm) and thickened (> 5mm) ONSD (ICC=0.947 and 0.972 respectively).

CONCLUSION: CT scan is a reliable substitute for MRI in measuring ONSD with almost perfect agreement between the two modalities. It might be good practice to include ONSD measurement in the initial evaluation of brain CT scan in any patient with suspected raised ICP.