Optic nerve ultrasonography may be used to help identify increased intracranial pressure (ICP) in a rapid, noninvasive and safe manner. The optic nerve is part of the central nervous system and is surrounded by cerebrospinal fluid. The sheath around the optic nerve is a continuation of the dura, and the subarachnoid space extends to the optic nerve. A rise in ICP transmits to the optic nerve, leading to optic disc swelling and eventually papilledema within seconds.1
Correct technique for orbital ultrasound requires placing a linear, high frequency probe transversely on the closed eyelid gently using bacitracin, or sterile lubrication to avoid trauma to the cornea, sclera, retina and/or globe. Too much pressure may lead to nausea, vomiting, and a pronounced vagal response.1 Ideally, the probe should be placed on superior-lateral aspect of the orbit and directed inferiorly and medially with the eyes closed as the patient lays supine (as depicted in the image below).2
In pediatric patients, it may be useful to evaluate for elevated ICP in cases of traumatic brain injury, VP shunt malfunction, chronic headaches, and craniosynostosis.3 Currently the only way to evaluate for ICP on exam is evidence of papilledema, which may be technically challenging. Ocular ultrasound is an innovative way to indirectly assess for increased ICP via sonographic evidence of papilledema. The hallmark finding is a smoothly contoured, hyperechoic prominence from the optic disc that protrudes into the posterior chamber.4
The image above is a still image of the eye looks like on ultrasound and includes useful arrows.
The ultrasound clips above are from our bedside ultrasound machine and show the papilledema from Fareed’s Hot Seat case. Note the “smoothly contoured, hyperechoic prominence” (aka bump) at the retina in comparison to the normal, which is flat.
References
1. Rajajee V, Vanaman M, Fletcher JJ, et al. Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocritical Care. 2011; 15: 506-515.
2. Dubourg J, Javouhey E, Geeraerts T, et al. Ultrasonography of optic nerve diameter for detection of raised intracranial pressure: a systematic review and meta-analysis. Intensive Care Medicine. 2011; 37: 1059-106
3. Wiegand C, Richards P. Measurement of intracranial pressure in children: a critical review of current methods. Developmental Medicine & Child Neurology. 2007; 49: 935-941.
4. Stone MB. Ultrasound diagnosis of papilledema and increased intracranial pressure in pseudotumor cerebri. The American Journal of Emergency Medicine. 2009; 27: 376.e1-376.e2.
5 Podolsky SR, Dickman E. Images in Emergency Medicine. Annals of Emergency Medicine. 2009; 53: e1-e2.
