Real-time optic nerve sheath diameter reduction measured with bedside ultrasound after therapeutic lumbar puncture in a patient with idiopathic intracranial hypertension.

Idiopathic intracranial hypertension (IIH), also referred to as pseudotumor cerebri, is a condition of raised intracranial pressure (ICP) with unknown etiology. Sonographic measurement of optic nerve sheath diameter (ONSD) has been shown to be a reliable, noninvasive method to characterize elevated ICP in a variety of settings. However, little is known about the immediate response of ONSD to an acute reduction in ICP after lumbar puncture. We describe a case of an emergency department patient with IIH in whom we identified real-time change in ONSD correlated with a decrease in cerebrospinal fluid pressure after a therapeutic lumbar puncture. Ocular ultrasound and ONSD measurements were performed by a trained provider using a 9- to 13-MHz linear transducer and an ultrasound machine with ocular software package and low mechanical index settings for data collection (MTurbo; SonoSite Inc, Bothell, WA). The ONSD was measured 30 minutes prior to and 30 minutes after a therapeutic lumbar puncture. Opening and closing pressures were recorded. Optic nerve sheath diameter measurements correlated with ICP as measured by opening and closing lumbar puncture pressures and showed an acute reduction in ONSD within 30 minutes after lumbar puncture. Sonographic measurement of ONSD reduction may be a novel, noninvasive and convenient way to follow acute reductions in ICP. Further investigation is necessary in order to validate this finding.