Abstract
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.
Highlights
1.1 Intracranial HypertensionIntracranial hypertension defined as sustained (>5 min) elevation of intracranial pressure (ICP) of >20 mmHg in adult (Susan et al, 2007) can result in serious neurological consequences if untreated
Optic nerve sheath diameter (ONSD) measurement using brain magnetic resonance imaging (MRI) has been shown to correlate well with invasively measured ICP, little research has been conducted on the ONSD measurement using computerized tomography (CT) in correlation with ICP
Similar agreement was obtained when cases stratified into normal (≤ 5mm) and thickened (> 5mm) ONSD (ICC=0.947 and 0.972 respectively)
Summary
1.1 Intracranial HypertensionIntracranial hypertension defined as sustained (>5 min) elevation of intracranial pressure (ICP) of >20 mmHg in adult (Susan et al, 2007) can result in serious neurological consequences if untreated. Direct ventriculostomy is the gold standard method for measuring ICP; this test is invasive and in addition to the technical difficulties carries risks of infection and hemorrhage (Rickert & Sinson, 2003; Miller, 1987). Interest has been turned into the use of the optic nerve sheath diameter (ONSD) to provide a noninvasive surrogate marker for early-elevated ICP. This utilizes the fact that optic nerve with its CSF-filled sheath is anatomically considered part of the brain and when ICP is increased, the optic nerve sheath distends (Hansen & Helmke, 1996) and this transmission of raised ICP into the optic nerve sheath has been recognized for many years (Geeraerts et al, 2008). This study was done to investigate whether CT scan can reliably replace MRI in measuring ONSD
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