344 Correlation of Sonographic Measured Optic Nerve Sheath Diameter and Lumbar Puncture Opening Pressure in Emergency Department Headache Patients

Ocular nerve sheath diameter (ONSD) greater than 5mm historically has been to correlate with increased intracranial pressure. Most emergency department (ED) studies of ONSD utilize CT evidence of increased ICP as opposed to direct ICP measurements. Furthermore, these studies largely focus on the trauma patient. More recent ED studies not only call into question the above-mentioned 5.0mm ONSD threshold, but also the 20 cm H2O threshold for elevated intracranial pressure. The aim of this study was to assess the sensitivity and specificity of ONSD for identifying patients requiring urgent or emergent intervention. A retrospective chart review was performed on 252 charts going back 2.5 years. Charts were extracted from the ED ultrasound database specifically searching patients who had ONSD measurements over the 2.5-year study period. Ultimately, 34 patients met criteria for inclusion in the study. Inclusion criteria consisted of patients 18 years of age, presented to the ED with headache, no documented recent history of head trauma, ONSD measured, and lateral decubitus lumbar puncture opening pressure recorded for the same visit. The patient records were reviewed for ED intervention and operative intervention. Discharge summary and clinic notes were reviewed for final diagnosis and outpatient management. We deemed patients with elevated ICP requiring emergent to urgent intervention as “clinically significant” elevated ICP. Bilateral sonographic ONSDs were averaged and recorded. A receiver operator characteristic (ROC) curve was built to compare ONSD to clinically significant elevated ICP. We also calculated the sensitivity and specificity of ONSD cut offs of 5.0 mm, 5.5 mm, and 6.0 mm for identifying clinically significant elevated ICP. In our group of 34 patients, 9 were found to have clinically significant elevated ICP. Eight patients had idiopathic intracranial hypertension and 1 patient had venous sinus thrombosis. Among the clinically significant group the average opening pressure was 46 cm H2O with an average ONS diameter of 6.2 mm. There were 18 patients with an opening pressure greater than 20 however, deemed not clinically significant. Twelve subjects were diagnosed with headache of uncertain etiology, 3 with viral meningitis, and 3 with new onset seizure. The average opening pressure in this group was 25 cm H2O with an average ONSD of 4.9 mm. There were 7 patients with an opening pressure less than 20 cm H2O with an average opening pressure of 17 cm of H2O and average ONSD of 5.0 mm. 4 subjects were diagnosed with headache of uncertain etiology, 1 subject with encephalitis, 1 subject with salicylate toxicity, and 1 subject with new-onset seizure. Based on this data, a ROC curve was generated and an ONSD greater than 5.5 mm was found to be a good predictor of clinically significant elevation in ICP with a sensitivity of 89% and specificity of 85%. The sensitivity and specificity of the 5.0 mm cutoff for clinically significant elevated ICP was 100% and 46%, respectively. The sensitivity and specificity of the 6.0mm cutoff was 67% and 100% respectively. A sonographic ONSD greater than 5.5 mm is both sensitive and specific for elevated intracranial pressure that requires urgent or emergent intervention.