"Ultrasound assessment of the diameter of the optic nerve sheath can be used as a bedside test for early diagnosis of raised intracranial tension in head injury, researchers from India report.

"Elevated intracranial pressure is a challenging and potentially fatal complication of acute head trauma," Dr. Ravishankar Goel and colleagues from Mumbai write in the May issue of Injury.

While CT scan is the gold standard in diagnosis of intracranial hypertension, its cost, availability and requirement of patients to be transported are limitations to its use, they point out. The optic nerve sheath is in direct communication with the subarachnoid cavity of the brain and an increase in its diameter can be used as a measure of raised intracranial pressure, they explain.

Dr. Goel and his team, from the LTM Medical College and LTMG Hospital, analyzed the efficacy of optic nerve ultrasound for detecting increased intracranial pressure in 100 patients admitted with head injury to their unit between 2006 and 2007. After appropriate clinical assessment and CT scanning, high resolution ultrasound assessment of the optic nerve sheath diameter was carried out through closed eyelids in all the patients.

Optic nerve sheath diameters above five mm in adults, 4.5 mm in children less than 15 years and four mm in infants were considered abnormal.

The mean optic nerve sheath diameter in 73 patients with CT-confirmed intracranial hypertension was 5.8 mm as compared to 3.5 mm among those with a normal CT scan, Dr. Goel and colleagues report.

The sensitivity, specificity and positive predictive value of optic nerve ultrasound in diagnosis of raised intracranial tension were 98.6 per cent, 92.6 per cent and 96.3 per cent respectively, they found.

Clinical examination, however, showed a poor correlation with CT scan in diagnosis of raised intracranial pressure, they note.

"Optic nerve ultrasound can be helpful in avoiding the need for CT in some unstable patients, triage of mass casualties, decisions about transfer from remote areas to hospitals with CT scanning facilities, and in serial follow-up of patients with a hematoma too small to require evacuation," Dr. Goel told Reuters Health.

When used along with near infrared spectroscopy (NIRS), which can localize the site of cerebral hematoma, it "may substitute the need of CT scan," he added.


Injury 2008;39:519-524."