gms | German Medical Science

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 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 150 patients (age range 0 to 18 years) diagnosed with tumor (n=40), hydrocephalus (n=42), and other intracranial pathologies (n=68). Bilateral ONSD was quantified by ultrasound in a standardized way, i.e. 3 mm behind the optical nerve papilla using an 11MHz linear array transducer. 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 ± 0.88 and 5.7 ± 0.89 mm for ultrasound and MRI, respectively. There was a strong positive correlation between ONSD measured on MRI compared to ultrasound (r= 0.976, p< 0.01). Bland and Altman analysis of the two methods showed a mean bias of 0.078 mm with limits of agreement of -0.3 and 0.5 mm. 95% of the values were within the limits of agreement. A repeated measures correlation (rrm) in 9 patients showed an excellent value (rrm= 0.94, p<0.01) as well.

Conclusion: MRI-based determination of ONSD can serve as a reliable alternative if ultrasound assessment of ONSD is not possible for various reasons. The difference of US and MRI ONSD is low and insignificant, thus both values can complement each other in the daily routine diagnostic setup.