Optic nerve sonography reliably indicates intracranial pressure

May 26, 2008

Ultrasound measurement of optic nerve sheath diameter can gauge intracranial pressure in patients who cannot tolerate invasive assessments. Sonography has proved useful in brain-injured pediatric patients, and a recent study confirmed that optic nerve sheath diameter correlates with intracranial pressure in adults with brain injuries.

Ultrasound measurement of optic nerve sheath diameter can gauge intracranial pressure in patients who cannot tolerate invasive assessments. Sonography has proved useful in brain-injured pediatric patients, and a recent study confirmed that optic nerve sheath diameter correlates with intracranial pressure in adults with brain injuries.

Dr. Theodoros Soldatos and colleagues at Attikon University Hospital and General State Hospital of Athens published their study in Critical Care, which made it available May 13. They studied 76 critical care patients, 50 who presented with brain injuries and 26 controls with no intracranial pathologies.

The researchers evaluated each brain-injured patient clinically with the Glasgow Coma Scale and the semiquantitative neuroimaging Marshall Scale. They categorized 18 patients with a Marshall Scale rating of I and a Glasgow Coma Scale rating of greater than 8 as having moderate brain injury. The other 32 patients had severe brain injury, with a Marshall Scale rating of II to VI and a Glasgow Coma Scale score less than or equal to 8.

Transcranial Doppler sonography measured intracranial pressure on all patients at the same time their optic nerve sheath diameter was measured. Those patients with severe brain injuries also had their intracranial pressure measured with an intraparenchymal catheter.

The researchers found the control patients had an optic nerve sheath diameter of 3.6±0.6 mm and an intracranial pressure measured with Doppler ultrasound of 10.3±3.1 mm Hg, while the patients with severe brain injuries had an optic nerve sheath diameter of 6.1±0.7 mm and intracranial pressure of 26.2±8.7 mm Hg. The patients with moderate brain injuries had an optic nerve sheath diameter of 4.2±1.2 mm and intracranial pressure of 12.0±3.6 mm Hg.

The investigators found that optic nerve sheath diameter of patients with severe brain injury strongly correlated with intracranial pressure measured with Doppler ultrasound as well as with invasive intracranial pressure measurements. A measurement of 5.7 mm of the optic nerve sheath was the best cutoff measurement for the prediction of elevated intracranial pressure, with a sensitivity of 74.1% and 100% specificity.

The researchers concluded that optic nerve sheath diameter can be used as an additional noninvasive diagnostic tool to alert clinicians to increased intracranial pressure, especially in brain-injured adults who cannot tolerate invasive means of measurement.