Optic Nerve Sheath Ultrasound for the Bedside Diagnosis of Intracranial Hypertension: Pitfalls and Potential

Raised intracranial pressure is a complication not just of traumatic brain injury and other acute cerebral insults, but also of a number of general medical conditions. Bedside diagnosis can be difficult; early clinical signs may be misinterpreted, and reliance on cross-sectional imaging studies may further delay diagnosis. Ultrasound is a readily available imaging modality in most critical care areas, and examination of the optic nerve sheath by bedside ultrasound allows detection of changes in diameter which may indicate intracranial hypertension. This paper reviews optic nerve sheath anatomy as a basis for its potential to provide a window on changes within the intracranial cerebrospinal fluid (CSF) space, the technique of sonographic measurement of optic nerve sheath diameter (ONSD), the evidence for correlation with intracranial pressure, and the comparison of ONSD with the ‘gold standard’ method of intracranial pressure assessment.