Theme: neurology--optic nerve sheath diameter measurement as a risk marker for significant intracranial hypertension.

Raised intracranial pressure (ICP) is a frequent condition in many medical and surgical situations and is often difficult to detect. Noninvasive estimates of raised ICP are of interest to allow rapid detection of significant intracranial hypertension. In the anterior part of the optic nerve, the sheath is distensible and can inflate in the case of raised pressure in the cerebrospinal fluid. Measurement of optic nerve sheath diameter using ocular sonography or MRI has been shown to correctly estimate the risk of raised ICP in various settings, including traumatic brain injury. Ocular sonography is simple, rapid, noninvasive and can be performed at the patient's bedside, but it requires training and experience. The cut-off value for ICP greater than 20 mmHg is 5.8 mm, with a 90% probability of correct diagnosis. When raised ICP is suspected, but invasive ICP monitoring cannot be used or is not clearly recommended, this estimation of the risk of raised ICP may be of great clinical value, aiding in the detection of patients at risk of raised ICP.