Optic nerve sonography in the diagnostic evaluation of adult brain injury

Abstract

Introduction: The optic nerve sheath diameter (ONSD) may be increased in brain-injured patients, especially children, with intracranial hypertension. We investigated whether measurements of ONSD correlated with simultaneous noninvasive and invasive measurements of the intracranial pressure (ICP) in brain-injured adults.

Methods: Seventy-six critical care patients (58 males; 47 +/- 18 years old) were included in the study. Fifty patients suffered from brain injury, whereas 26 had no intracranial pathology and served as control individuals. Initially, brain-injured patients were evaluated clinically (Glasgow Coma Scale) and using a semiquantitative (I to VI) neuroimaging scale (Marshall Scale). Thereafter, the patients were divided into those with moderate (Marshall Scale = I and Glasgow Coma Scale > 8 [n = 18]) and severe (Marshall Scale = II to VI and Glasgow Coma Scale < or =8 [n = 32]) brain injury. All patients underwent noninvasive measurement of the ICP (estimated ICP) by transcranial Doppler sonography, and synchronous ONSD measurements by optic nerve sonography. Finally, invasive ICP measurement using an intraparenchymal catheter was performed in patients with severe brain injury.

Results: ONSD and estimated ICP were both significantly increased (6.1 +/- 0.7 mm and 26.2 +/- 8.7 mmHg, respectively; P < 0.0001) in patients with severe brain injury as compared with patients with moderate brain injury (4.2 +/- 1.2 mm and 12.0 +/- 3.6 mmHg) and compared with control individuals (3.6 +/- 0.6 mm and 10.3 +/- 3.1 mmHg). Furthermore, in patients with severe brain injury the ONSD measurements were strongly correlated with estimated ICP values (r = 0.80, P < 0.0001) as well as with the neuroimaging scale results (r = 0.82, P < 0.001). In the patients with severe brain injury, ONSD measurements correlated with invasive ICP values (r = 0.68, P = 0.002). The best cut-off value of ONSD for predicting elevated ICP was 5.7 mm (sensitivity = 74.1% and specificity = 100%).

Conclusion: ONSD measurements correlate with noninvasive and invasive measurements of the ICP, and with head computed tomography scan findings in brain-injured adults. Hence, optic nerve sonography may serve as an additional diagnostic tool that could alert clinicians to the presence of elevated ICP, whenever invasive ICP evaluation is contraindicated and/or is not available. This trial is International Standard Randomised Controlled Trial Number registered (ISRCTN 91941687).

Figure 1

Imaging findings of a brain-injured adult. (a) Brain computed tomography (CT) scan of a patient showing a midline shift of more than 5 mm and a nonevacuated lesion of more than 25 ml. (b) Transorbital sonography of the same patient documenting increased optic nerve sheath diameter.

Figure 2

ONSD versus eICP. Shown are the optic nerve sheath diameter (ONSD) measurements plotted against the noninvasive intracranial pressure (eICP) in patients with severe brain injury (group C; n = 32).

Figure 3

ONSD versus invasive ICP. Shown are the optic nerve sheath diameter (ONSD) measurements plotted versus the invasive intracranial pressure (ICP) in the patients with severe brain injury (group C; n = 32).

Figure 4

Predictive value of ONSD. Presented is a receiver operating characteristic curve showing the predictive value of the optic nerve sheath diameter (ONSD; the cut-off value is 5.7 mm) for elevated intracranial pressure (ICP; ≥20 mmHg).