This prospective study evaluated whether ultrasonographic optic nerve sheath diameter (ONSD) measurements could be used to monitor intracranial pressure (ICP).
Using ultrasound, investigators measured ONSD prior to lumbar puncture (LP) in 60 patients. They analyzed the correlation between the ONSD and ICP on admission, and the changes in ONSD and ICP from admission through follow-up.
On admission, ONSD strongly correlated with LP opening pressure, with a Pearson correlation (r) of 0.798 (P<0.001). Twenty-five patients with elevated ICP completed follow-up, and these patients also showed a strong correlation between ONSD and opening pressure at baseline (r 0.724; P<0.001).
During follow-up, LP opening pressure and ONSD returned to normal ranges. The change in ONSD strongly correlated with the change in LP opening pressure (r 0.702; P<0.001). At follow-up after normalization of the ICP, the ONSD measurements were similar between patients who presented with mildly elevated and higher elevated ICP (3.49 mm vs. 3.51 mm; P=0.778).
There were a few limitations of the study. First, the etiologies of elevated ICP were acute pathologies, such as cerebral infection and hydrocephalus, and therefore the results may not be directly applicable to chronic causes of raised ICP, such as idiopathic intracranial hypertension. Second, ICP was estimated by LP opening pressure, which is not a direct measurement of the ICP. Third, the range of LP opening pressures for this patient cohort was between 200 and 400 mm H20, and further work will be required to determine if the study results apply to opening pressures outside of this range. Finally, dilation of the ONSD can occur with other pathologies, such as perioptic neuritis, and therefore this finding is not limited to elevated ICP.
This study suggests that ONSD measured by ultrasound can dynamically detect changes in ICP. In the correct clinical context, ultrasound can be a helpful noninvasive adjunct tool to detect raised ICP and monitor for worsening or improving disease.