Measuring Intracranial Pressure: Is Ultrasound Acceptable?

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A study by researchers at Jilin University in Changchun, China, furthers the case for orbital/optic nerve ultrasound’s potential as an alternative to lumbar puncture for measuring changes in intracranial pres­sure (ICP).¹ Previously, the researchers confirmed that ultrasonographic measurements of optic nerve (ON) sheath diameter could be used to identify patients with elevated ICP.²

Dynamic assessments. For this study, the researchers measured both ON sheath diameter and ICP in 60 pa­tients who had been admitted for lumbar puncture. Of those, 37 were found to have elevated ICP, most caused by cerebral infection. One month later, following treat­ment, the 25 patients not lost to follow-up underwent an additional round of measurements.

In both situations—upon admission and after treat­ment—the ON sheath diameter and lumbar puncture measurements were strongly correlated. What’s more, there was no difference in mean ON sheath diameter between patients with higher or lower levels of elevated ICP.

The researchers speculated that the elasticity of the ON sheath may explain why sheath diameter examina­tions can be used to dynamically assess variations in ICP. They also noted that the technique is easy to learn, has high interobserver reliability, and may be generalizable and applicable in a variety of potential clinical settings.

Clinical implications. “This study adds further evi­dence [supporting] the sensitivity and specificity of ultrasonography for the purpose of determining in a noninvasive manner whether or not there is elevated ICP,” said Andrew G. Lee, MD, at the Blanton Eye Insti­tute at Houston Methodist Hospital.

In fact, Dr. Lee said in an accompanying editor’s note, he has used orbital ultrasound as either an ad­junct or surrogate to actual direct measurement of ICP in a number of common clinical circumstances.³ Among them: differentiating difficult cases of pseudopapill­edema from papilledema, and following patients who either refuse or cannot undergo lumbar puncture.

Nevertheless, Dr. Lee noted that the technique “is still in development.” And he agreed with the research­ers that larger studies are needed, in part to determine whether the results are generalizable at ICP levels out­side the study’s parameters. The maximum ICP value in the study was 400 mm H₂O, so the accuracy of the technique at higher levels is not clear.

Despite ultrasonography’s potential as a noninvasive alternative to lumbar puncture, Dr. Lee said, “Direct measurements of ICP remain the gold standard.”

—Miriam Karmel

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1 Wang L et al. JAMA Ophthalmol. 2018;136(3):250-256.

2 Wang L et al. PLoS One. 2015;10(2):e0117939.

3 Lee AG. JAMA Ophthalmol. 2018;136(3):256.

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Relevant financial disclosures—Dr. Lee: None.

For full disclosures and the disclosure key, see below.

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