Correlation Between Ultrasonographic Optic Nerve Sheath Diameter and Intracranial Pressure in Patients with Aneurysmal S
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LETTERS TO THE EDITOR
Correlation Between Ultrasonographic Optic Nerve Sheath Diameter and Intracranial Pressure in Patients with Aneurysmal Subarachnoid Hemorrhage Varun Suresh1*, Saurabh Sharma2 and Anurag Aggarwal3 © 2020 Springer Science+Business Media, LLC, part of Springer Nature and Neurocritical Care Society
We read with interest the research work published by Zoerle et al. [1] on correlation between optic nerve sheath diameter (ONSD) and intracranial pressure (ICP) in patients with intracranial aneurysm presenting as subarachnoid hemorrhage (SAH). We appreciate the author’s effort in successfully correlating magnetic resonance imaging (MRI)-measured ONSD with trans-bulbar ultrasonography (TBUS)-measured values. This correlation is certainly important as TBUS-measured ONSD provides point-of-care benefit along with its feasibility for repeatable noninvasive measurements. However, we have a few methodological concerns and we find some limitations which the authors have not addressed in their article. We find the author’s method of ONSD measurement in T2-weighted MRI impeccable; however, the method followed with TBUS is questionable. It is stated in the study that the distension of ONS is attributed to a rise in ICP and consequent shift of cerebrospinal fluid (CSF) into the ONS. CSF space within ONS is narrow with a classic volume of 0.1–0.2 mm3. This volume supposedly increases in raised ICP scenarios as in aneurysmal SAH. Fluid-filled spaces are characteristically hypo-echoic in ultrasound and hyper-intense in T2-weighted MRI. The authors measured ONSD as the *Correspondence: [email protected] 1 Department of Anaesthesiology, Government Medical College, Thiruvananthapuram 695011, Kerala, India Full list of author information is available at the end of the article
This article refers to the original article https://doi.org/10.1007/s1202 8-020-00970-y. A response to this letter can be found at https://doi.org/10.1007/s1202 8-020-01088-x.
distance between the external borders of the hyperechoic area surrounding the optic nerve with electronic calipers at 3 mm behind the fundus of the eye, perpendicular to the longitudinal axis of optic nerve. Hence, doesn’t this represent the optic nerve diameter rather than ONSD? Previous studies have measured ONSD as a distance between hypoechoic area surrounding the optic nerve as such [2]. We presume that this could probably be the reason for lower mean ONSD with TBUS compared to MRI in this study (6.38 ± 0.39 mm with TBUS versus 6.43 ± 0.6 mm using MRI). Further, six cases (30%) among the study population were elderly patients with age ≥ 60 years. The ONS is characterized by septations and trabeculae which increase with age [3]. Usually, studies assessing ONSD exclude patients older than 60 years due to this reason. It is understandable that the incidence of aneurysmal SAH is higher as age progresses and highest at the fifth and sixth decade of life, but when the study variable is ONSD authors could have excluded patients older than 60 years. It coul
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