Optic nerve sheath diameter ultrasonography [Neurosurgery Wiki]

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====== Optic nerve sheath diameter ultrasonography ======

{{ ::optic_nerve_sheath_diameter_ultrasonography.png?400|}}



[[Optic nerve sheath diameter]] ultrasonography is strongly correlated with invasive [[ICP]] measurements and may serve as a sensitive and noninvasive method for detecting elevated ICP in [[TBI]] patients after decompressive craniectomy
((Wang J, Li K, Li H, Ji C, Wu Z, Chen H, Chen B. Ultrasonographic optic nerve
sheath diameter correlation with ICP and accuracy as a tool for noninvasive
surrogate ICP measurement in patients with decompressive craniotomy. J Neurosurg.
2019 Jul 19:1-7. doi: 10.3171/2019.4.JNS183297. [Epub ahead of print] PubMed
PMID: 31323632.
)).

[[Optic nerve sheath diameter]] measured by [[transorbital ultrasound imaging]] is an accurate method for detecting [[intracranial hypertension]] that can be applied in a broad range of settings. It has the advantages of being a non-invasive, bedside test, which can be repeated multiple times for re-evaluation
((Beare NA, Kampondeni S, Glover SJ, Molyneux E, Taylor TE, Harding SP, Molyneux
ME. Detection of raised intracranial pressure by ultrasound measurement of optic 
nerve sheath diameter in African children. Trop Med Int Health. 2008
Nov;13(11):1400-4. doi: 10.1111/j.1365-3156.2008.02153.x. Epub 2008 Oct 13.
PubMed PMID: 18983275; PubMed Central PMCID: PMC3776606.)).

Evolution of [[ultrasound]] technology and the development of high frequency (> 7.5 MHz) linear probes with improved spatial resolution have enabled excellent views of the [[optic nerve sheath]]. 

The optic nerve sheath diameter (ONSD), measured at a fixed distance behind the retina has been evaluated to diagnose and measure intracranial hypertension in traumatic brain injury and intracranial hemorrhage
((Geeraerts T, Merceron S, Benhamou D, Vigué B, Duranteau J. Non-invasive assessment of intracranial pressure using ocular sonography in neurocritical care patients. Intensive Care Med. 2008;34:2062–7.))
((Moretti R, Pizzi B. Optic nerve ultrasound for detection of intracranial hypertension in intracranial hemorrhage patients: Confirmation of previous findings in a different patient population. J Neurosurg Anesthesiol. 2009;21:16–20.)).

The [[optic nerve sheath]] is fairly easy to visualize by [[ultrasonography]] by insonation across the [[orbit]] in the axial plane. A-mode ultrasonography was used to view the optic nerve sheath more than four decades ago; B-mode scanning was performed subsequently to assess intraocular lesions
((Gangemi M, Cennamo G, Maiuri F, D'Andrea F. Echographic measurement of the optic nerve in patients with intracranial hypertension. Neurochirurgia (Stuttg) 1987;30:53–5.)).


Shirodkar et al., studied the efficacy of ONSD measurement by ultrasonography to predict intracranial hypertension. The case mix studied included meningoencephalitis, stroke, intracranial hemorrhage and metabolic encephalopathy. Using cut-off values of 4.6 mm for females, and 4.8 mm for males, they found a high level of sensitivity and specificity for the diagnosis of intracranial hypertension as evident on CT or MRI imaging
((Shirodkar CG, Rao SM, Mutkule DP, Harde YR, Venkategowda PM, Mahesh MU. Optic nerve sheath diameter as a marker for evaluation and prognostication of intracranial pressure in Indian patients: An observational study. Ind J Crit Care Med. 2014;18:728–734)).

There is wide variation reported in the optimal cut-off values, when ONSD was compared with invasive ICP monitoring, ranging from 4.8 to 5.9 mm
((Rajajee V, Vanaman M, Fletcher JJ, Jacobs TL. Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care. 2011;15:506–15.))
((Geeraerts T, Launey Y, Martin L, Pottecher J, Vigué B, Duranteau J, et al. Ultrasonography of the optic nerve sheath may be useful for detecting raised intracranial pressure after severe brain injury. Intensive Care Med. 2007;33:1704–11.)).

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Padayachy et al present a method for assessment of [[optic nerve sheath]] ONS pulsatile dynamics using [[transorbital ultrasound imaging]]. A significant difference was noted between the patient groups, indicating that deformability of the ONS may be relevant as a noninvasive marker of raised ICP
((Padayachy L, Brekken R, Fieggen G, Selbekk T. Pulsatile Dynamics of the Optic 
Nerve Sheath and Intracranial Pressure: An Exploratory In Vivo Investigation.
Neurosurgery. 2016 Jul;79(1):100-7. doi: 10.1227/NEU.0000000000001200. PubMed
PMID: 26813857; PubMed Central PMCID: PMC4900421.
)).


===== Indications =====

[[Optic nerve sheath diameter ultrasonography indications]]


===== Case series =====
[[Optic nerve sheath diameter ultrasonography case series]].

===== References =====