Utility of optic nerve ultrasonography in head injury

Abstract

Background: CT has evolved as the gold standard for evaluation of head injury, but early CT is not always possible. Bedside ultrasonography is available in most trauma units and optic nerve ultrasound (ONUS) examination should be feasible.

Objective: To evaluate the role of ONUS for people with head injury.

Setting: Tertiary care trauma service in a teaching hospital in a large metropolitan city in India.

Design: Prospective, blinded, observational study.

Methods: From April 2006 to January 2007, all adult patients with head injury but without obvious ocular trauma, for whom it was possible to perform CT, were enrolled. Using a 7.5-MHz ultrasonographic probe on the closed eyelids, optic nerve sheath diameter (ONSD) was measured on either side. A mean binocular ONSD less than 5.00 mm was considered normal. Cranial CT findings were used as a reference standard to evaluate ONUS.

Results: The study included 100 participants (72 men, 28 women, median age 28 years, median Glasgow Coma Scale score 11). Clinical features did not correlate with CT for signs of raised intracranial pressure (ICP). The mean binocular ONSD (5.8+/-0.57 mm) was significantly increased among individuals with signs of raised ICP on CT compared with the mean ONSD (3.5+/-0.75 mm) among those without such signs. ONUS revealed evidence of raised ICP in 74 cases (confirmed by CT in 72 cases), 59 of whom had significant intracranial haematoma needing surgical evacuation. Of the 26 cases with negative ONUS, confirmed by CT in 25 cases, only 1 needed surgical intervention for drainage of intracranial haematoma. ONUS was false positive for two and false negative for one person. The sensitivity of ONUS in detecting elevated ICP was 98.6%, specificity 92.8%, positive predictive value 97.26% and negative predictive value 96.3%.

Conclusion: ONUS has potential as a sensitive bedside screening test for detecting raised ICP and the presence of intracranial haematoma needing surgical intervention in adult head injury. This can be of immense help for unstable patients, in mass casualty situations and in remote locations.