Optic nerve sheath diameter and lumbar puncture opening pressure in nontrauma patients suspected of elevated intracranial pressure.

OBJECTIVE

The purpose of this study was to determine if patients with nontraumatic causes of elevated intracranial pressure (ICP) could be identified by ultrasound measurement of optic nerve sheath diameter (ONSD). It was hypothesized that an ONSD greater than or equal to 5 mm would identify patients with elevated ICP.

METHOD

This was a prospective observational trial comparing ONSD with ICP measured by opening pressure manometry on lumbar puncture (LP). The cohort consisted of a convenience sample of adult patients presenting to the emergency department, requiring LP. The ONSD measurement was performed before computed tomography and LP. The physician performing the LP was blinded to the result of the ONSD measurement. An opening pressure on manometry of greater than or equal to 20 cm H2O and an ONSD greater than or equal to 5 mm were considered elevated.

RESULTS

Fifty-one patients were included in our study, 24 (47%) with ICP greater than or equal to 20 cm H2O and 27 (53%) with ICP less than 20 cm H2O. The sensitivity of ONSD greater than or equal to 5 for identifying elevated ICP was 75% (95% confidence interval, 53%-90%) with specificity of 44% (25%-65%). The area under the receiver operator characteristic curve was 0.69 (0.54-0.84), suggesting a relationship between ONSD and ICP.

CONCLUSION

An ONSD greater than or equal to 5 mm was associated with elevated ICP in nontraumatic causes of elevated ICP. Although a relationship exists, a sensitivity of 75% does not make ONSD measurement an adequate screening examination for elevated ICP in this patient population.