Optic nerve sheath diameter

Optic nerve sheath diameter on initial brain CT, raised intracranial pressure and mortality after severe TBI: an interesting link needing confirmation

Authors: Masquère P, Bonneville F, Geeraerts T.

Optic nerve sheath diameter (ONSD) enlargement on initial computed tomography (CT) scan has been found to be associated with increased mortality after severe traumatic brain injury. This could offer the possibility to detect patients with raised intracranial pressure requiring urgent therapeutic interventions and/or invasive intracranial monitoring to guide the treatment. The method to measure ONSD using CT scan, however, needs further confirmation. Moreover, the link between ONSD enlargement on initial CT scan and raised intracranial pressure also needs to be confirmed by further studies.

Sonographic Optic Nerve Sheath Diameter as an Estimate of Intracranial Pressure in Adult Trauma

Authors: Strumwasser A, Kwan RO, Yeung L, Miraflor E, Ereso A, Castro-Moure F, Patel A, Sadjadi J, Victorino GP.

Department of Surgery, University of California, San Francisco-East Bay, Oakland, California.

BACKGROUND: Intracranial pressure (ICP) is currently measured with invasive monitoring. Sonographic optic nerve sheath diameter (ONSD) may provide a noninvasive estimate of ICP. Our hypothesis was that bedside ONSD accurately estimates ICP in acutely injured patients. The specific aims were (1) to determine the accuracy of ONSD in estimating elevated ICP, (2) to correlate ONSD and ICP in unilateral and bilateral head injuries, and (3) to determine the effect of ICP monitor placement on ONSD measurements.

MATERIALS AND METHODS: A blinded prospective study of adult trauma patients requiring ICP monitoring was performed at a University-based urban trauma center. The ONSD was measured by ultrasound pre- and post-placement of an ICP monitor (Camino Bolt or Ventriculostomy).

RESULTS: One-hundred fourteen measurements were obtained in 10 trauma patients requiring ICP monitoring. Pre- and post-ONSD were compared with side of injury in the presence of an ICP monitor. ROC analysis demonstrated ONSD poorly estimates elevated ICP (AUC = 0.36). Overall sensitivity, specificity, PPV, NPV, and accuracy for estimating ICP with ONSD were 36%, 38%, 40%, 16%, and 37%. Poor correlation of ONSD to ICP was observed with unilateral (R(2) = 0.45, P < 0.01) and bilateral (R(2) = 0.21, P = 0.01) injuries. ICP monitor placement did not affect ONSD measurements on the right (P = 0.5), left (P = 0.4), or right and left sides combined (P = 0.3).

CONCLUSIONS: Sonographic ONSD as a surrogate for elevated ICP in lieu of invasive monitoring is not reliable due to poor accuracy and correlation.

Using MRI of the optic nerve sheath to detect elevated intracranial pressure

Authors: Heidi Harbison Kimberly and Vicki E Noble

The current gold standard for the diagnosis of elevated intracranial pressure (ICP) remains invasive monitoring. Given that invasive monitoring is not always available or clinically feasible, there is growing interest in non-invasive methods of assessing ICP using diagnostic modalities such as ultrasound or magnetic resonance imaging (MRI). Increased ICP is transmitted through the cerebrospinal fluid surrounding the optic nerve, causing distention of the optic nerve sheath diameter (ONSD). In this issue of Critical Care, Geeraerts and colleagues describe a non-invasive method of diagnosing elevated ICP using MRI to measure the ONSD. They report a positive correlation between measurements of the ONSD on MRI and invasive ICP measurements. If the findings of this study can be replicated in larger populations, this technique may be a useful non-invasive screening test for elevated ICP in select populations.

Optic nerve sheath diameter, intracranial pressure and acute mountain sickness on Mount Everest: a longitudinal cohort study

Authors: A I Sutherland1, D S Morris2, C G Owen3, A J Bron4, R C Roach5 

Objective: To investigate the association of optic nerve sheath diameter (ONSD), as a correlate of intracranial pressure (ICP), with acute mountain sickness (AMS).

Conclusions: ONSD increases at high altitude, and this increase is associated with more severe symptoms of AMS. Given the linkage between ONSD and ICP, these results strongly suggest that intracranial pressure plays an important role in the pathophysiology of AMS.

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