Article
The correlation of optic nerve sheath diameter (ONSD) using ultrasound and magnetic resonance imaging (MRI) in pediatric neurosurgical patients
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Authors
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Susanne Kerscher
- Universitätsklinikum Tübingen, Klinik für Neurochirurgie, Bereich Pädiatrische Neurochirurgie, Tübingen, Deutschland
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Konstantin Hockel
- Universitätsklinikum Tübingen, Klinik für Neurochirurgie, Tübingen, Deutschland
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Martin Schuhmann
- Universitätsklinikum Tübingen, Klinik für Neurochirurgie, Bereich Pädiatrische Neurochirurgie, Tübingen, Deutschland
| Published: | June 9, 2017 |
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Outline
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Objective: Trans-orbital ultrasonographic measurement of the optic nerve sheath diameter (ONSD) is a sensitive, non-invasive and radiation-free technique to reliably identify potentially increased intracranial pressure (ICP) or, in case of a longitudinal assessment, changes of ICP over time. The spatial resolution of ultrasound is much higher than that of magnetic resonance imaging (MRI), thus ultrasound assessment is the gold standard of ONSD measurement. In uncooperative infants and small children awake determination of ONSD might be difficult or impossible. Thin slice T2-weighted MRI of the orbit, visualizing the optic nerve sheath, can serve as an alternative method to assess ONSD. MRI measurements have also their importance as previous values for comparison to a recent ultrasound assessment. This study thus investigates the accuracy and reliability of MRI versus ultrasound ONSD assessment in pediatric patients in neurosurgery.
Methods: The presented prospective study investigates 27 patients (age range 1 to 16 years) diagnosed with tumor (n=18), hydrocephalus (n=8), and other intracranial pathologies (n=1). Bilateral ONSD was quantified by ultrasound in a standardized way, i.e. 3 mm behind the optic nerve papilla using an 11MHz linear array transducer for a total of 3 measurements per eye. This was compared to simultaneously (usually within 24 hours) assessed ONSD on T2-weighted MRI of the orbit.
Results: Overall mean values for ONSD were 5.8 ± 0.9 and 5.7 ± 0.9 mm for ultrasound and MRI, respectively. There was a strong positive correlation between ONSD measured on MRI compared to ultrasound (r= 0.938, p< 0.0001). Bland and Altman analysis of the two methods showed a mean bias of -0.2 mm with limits of agreement of -0.8 and 0.4 mm. 24 out of 27 values were within the limits of agreement.
Conclusion: MRI-based determination of ONSD can serve as a reliable alternative if ultrasound assessment of ONSD is not possible for various reasons. It is of note, however, that MRI has the tendency to underestimate true ONSD. This needs to be taken into consideration when directly comparing ultrasound to MRI values in longitudinal assessment or in case MRI-based ONSD values are used to diagnose increased ICP according to thresholds. Large patients` series will be necessary to consolidate these first impressions.
