Sonographic assessment of the optic nerve sheath diameter in the diagnosis of idiopathic intracranial hypertension

Abstract Objective: Sonographic assessment of the optic nerve sheath diameter (ONSD) is a useful technique in detecting raised intracranial pressure (ICP) in neurocritical care patients. Its utility in idiopathic intracranial hypertension (IIH) is less known. The aim of this study was to evaluate the diagnostic accuracy of ONSD for detecting IIH. Material and methods: Ultrasound measurement of ONSD was performed in 19 patients with IIH and in 11 patients with different neurological diseases without raised ICP that required undergoing a lumbar puncture. The validity of this technique for diagnosing IIH was established with cerebrospinal fluid manometry values. Results: Patients with IIH showed significantly enlarged ONSD than those without IIH. The best cut-off point for detecting raised ICP was 6.3 mms, with a sensitivity, specificity and positive likelihood ratio of 94.7%, 90.9% and 10.4, respectively. After a therapeutic lumbar puncture an 87% of cases had a partial reduction of ONSD values. Conclusion: Sonographic assessment of ONSD seems to be a useful and reliable technique for detecting raised ICP. While the spinal manometry is not replaced in usual clinical settings, transorbital sonography alternatively allows a suitable and harmless screening of patients with suspected IIH. It would be desirable to perform an internal validation of the technique in each hospital in order to get the optimal cut-off point.