LAUSR

Clarification on Using Ultrasonography to Detect Intracranial Pressure To the Editor We read with great interest the article by Swanson et al1 concerning the possibility to detect an increase in intracranial pressure (ICP) using optical coherence tomography (OCT). We agree with the authors about the relative importance of the fundus examination in cases of increased ICP, as demonstrated by Hayreh and Hayreh,2 but we feel that there are points that need to be clarified. The authors state that the “ultrasonography of the optic nerve sheath diameter shows promise in diagnosing cases of severely elevated ICP, especially in acute situations, but has a sensitivity of only 11%.” This is true when we consider the studies referenced by the authors in which a B-scan ultrasonography was used, because this kind of measurement can be influenced, among others, by the so-called blooming effect. Moreover, B-scan ultrasonography can only detect an increase in the optical nerve diameter that is not typical of an intracranial hypertension, because an optic neuritis or an optic nerve glioma can show a similar picture. In these cases, an evaluation conducted with another ultrasonographic method, the standardized A-scan, can yield more precise results, even if it requires some skill and is slightly more difficult to perform.3 Using this technique, it is also possible to perform the 30° test that was introduced by Ossoinig.3 This is a measurement of the arachnoidal diameter in straight gaze that is remeasured in the maximal abduction of the eye (30° gaze); a decrease of the arachnoidal diameter of more than 5% proves the presence of subarachnoidal fluid and differentiates this fluid distension from either a solid thickening of the sheaths or a swelling of the pial and arachnoidal sheaths in cases of severe orbital congestions.4,5 Moreover, we believe that eTable 4 in the article’s Supplement needs further clarification, for it seems that papilledema was present among all 40 patients with craniosynostosis, and in the group of participants with normal ICP, all patients presented with papilledema and normal OCT results (21 eyes). However, in the group of high ICP (19 eyes), only 2 patients presented with papilledema and OCT parameters above the normal limits, meaning that 17 patients presented with normal OCT values with several false-negative results. Perhaps we misunderstood the data or there is a mistake in the table, but this seems to contradict the article’s conclusion.