PracticeUpdate: Neurology - Winter 2018

EXPERT OPINION 13

Ultrasound and MRI Both Detect Increased Intracranial Pressure to Complement Comprehensive Workup By Michael A. Williams MD Dr. Williams is Professor of Neurology

and Neurological Surgery at the University of Washington School of Medicine in Seattle, Washington.

R eliable methods of noninvasive intracranial pressure (ICP) estimation have been sought for decades. Multiple methods have been tried, including transcranial Dop- pler, distortion product otoacoustic emissions, measurement of tympanic membrane displacement, and, in this article by Patterson et al 1 , widening of the optic nerve sheath diameter (ONSD) by ultrasound or MRI in patients with papilledema (ie, idiopathic intrac- ranial hypertension [IIH]) or pseudopapilledema. The paper states that an MRI-detected ONSD of ≥6.0mm has 77% sensitivity and 83% specificity for “detecting increased ICP.” Yet, nowhere in the methods, the results, or the tables is a value for “increased ICP” provided. Do the authors mean the ability to discrim- inate between patients with papilledema and pseudopapilledema, which is not the same as increased ICP? The relationship between ultrasound ONSD and CSF opening pres- sure in Figure 2B has a weak coefficient of determination (R2) of 0.0324 for papilledema, and, by looking at the scatterplot, it is easy to see that no relationship between ONSD and opening pressure is to be found. The protocol was performed by a technician with over 30 years of experience with ocular ultrasonography, leading the authors to correctly state that “...the generalizability of our data may not be applicable to other practices.” Furthermore, the radiologist performing the MRI measurements was not masked to the diagnosis. Readers are advised to review this manuscript with caution, and they should not over-interpret its findings. Noninvasive methods of ICP estimation, including MRI or ultrasound-detected ONSD, are not sensitive, specific, or reliable enough to be used to make critical diagnostic or treatment decisions for IIH. When faced with a patient whose history, exam, and neuroimaging findings suggest IIH, the ICP should be measured at the very least by lumbar puncture, as the authors acknowledge. The risks of both false– positive and false–negative determination of increased ICP are too significant to rely on anything less. Reference 1. DF Patterson, ML Ho, JA Leavitt, et al. Comparison of ocular ultrasonography and magnetic resonance imaging for detection of increased intracranial pressure. Front Neurol 2018;9:278. www.practiceupdate.com/c/68076

" When faced with a patient whose history, exam, and neuroimaging findings suggest IIH, the ICP should be measured at the very least by lumbar puncture, as the authors acknowledge. "

VOL. 3 • NO. 3 • 2018