Ultrasound for Optic Nerve Sheath Diameter

Author: Stephen Alerhand, MD (EM Resident Physician, Icahn School of Medicine at Mount Sinai) (@SAlerhand) // Edited by: Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital)

Scenario

A 21 year-old heavy-set female with no prior medical history presents to your emergency department complaining of dull intermittent frontal headaches for the past 3 months. These headaches have no identified triggers, aggravators, or alleviators. They occur about three times daily, irrespective of position or time of day. They are associated with occasional nausea and transient binocular vision loss. She denies fever/chills, chest pain/shortness of breath, diarrhea, syncope, weakness. She has taken Ibuprofen 400 mg for these headaches but the medicine is bringing her less relief as time goes on. No other family members at home have had similar headaches.

Vital signs are within normal limits.

On exam, the patient is very well appearing without any visual deficits or other neurological findings.

The resident does not believe that this patient’s headache constitutes one of the acute dangerous headaches that must be ruled out immediately in the ED. Even if the resident had ordered a CT scan, he/she would have found it to be normal. In all likelihood, these headaches simply represent migraines that are not responding to Motrin anymore.  That being said, the resident tells the attending, could these headaches possibly represent pseudotumor cerebri… or benign intracranial hypertension… or idiopathic intracranial hypertension…or whatever they are calling it these days? Should he/she perform an LP and go down that path?

Literature

Blaivas M, Theodoro D, Sierzenski PR. Elevated intracranial pressure detected by bedside emergency ultrasonography of the optic nerve sheath. Acad Emerg Med 2003 Apr;10(4):376-81.

Type of Study: prospective blinded observational
Objective: to determine whether ONSD could accurately predict elevated intracranial pressure (EICP)
Results: n=35. 14 had EICP, all correctly predicted by ONSD >5 mm. Mean ONSD with EICP 6.27 mm versus 4.42 mm w/o EICP (p=0.001).
Conclusion: Bedside US may be useful for diagnosis of EICP

Irazuzta JE, Brown ME, Akhtar J. Bedside Optic Nerve Sheath Diameter Assessment in the Identification of Increased Intracranial Pressure in Suspected Idiopathic Intracranial Hypertension. Pediatr Neurol. 2015 Aug 28.

Type of Study: single-center, prospective, rater-blinded
Objective: to determine whether bedside OUS could identify elevated intracranial hypertension in patients aged 12-18 suspected of having idiopathic intracranial hypertension
Results: 13 patients in study, 10 of whom had elevated intracranial pressure. ONSD was able to predict or rule it out in all 13 patients.
Conclusion: Non-invasive assessment of ONSD could help identify patients with elevated intracranial pressure when idiopathic intracranial hypertension is suspected

Tayal VS, Neulander M, Norton HJ, et al. Emergency department sonographic measurement of optic nerve sheath diameter to detect findings of increased intracranial pressure in adult head injury patients. Ann Emerg Med. 2007 Apr;49(4):508-514.

Type of Study: prospective blinded observational
Objective: to determine whether bedside OUS of ONSD can accurately predict CT findings of elevated intracranial pressure in adult head injury patients
Results: n=59, 8 w/ ONSD > 5 mm that also had elevated intracranial pressure. Sensitivity 100% (68%-100%), specificity 63% (50%-76%).
Conclusion: Bedside ONSD has potential as sensitive screening test for elevated intracranial pressure in adult head injury.

Kimberly HH, Shah S, Marill K, Noble V. Correlation of optic nerve sheath diameter with direct measurement of intracranial pressure. Acad Emerg Med. 2008 Feb;15(2):201-4.

Type of Study: prospective blinded observational
Objective: to evaluate association between ONSD and ICP and to validate 5 mm threshold
Results: 38 OUS on 15 individual patients. ONSD > 5 mm detected ICP > 20 mmHg w/ sensitivity of 88% (47%-99%) and specificity 93% (78%-99%).
Conclusion: Study directly correlates ventriculostomy measurements of ICP w/ US ONSD measurements. Provides further support for use of ONSD as a noninvasive test for elevated ICP.

Dubourg J, Javouhey E, Geeraerts T, Messerer M, Kassai B. Ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure: a systematic review and meta-analysis. Intensive Care Med. 2011 Jul;37(7):1059-68.

Type of Study: meta-analysis
Objective: to evaluate diagnostic accuracy of US ONSD for assessment of intracranial hypertension
Results: n=231. Pooled sensitivity 0.90 (0.80-0.95), pooled specificity 0.85 (0.73-0.93)
Conclusion: ONSD showed good accuracy for diagnosing intracranial hypertension.

Karami M, Shirazinejad S, Shaygannejad V, et al. Transocular Doppler and optic nerve sheath diameter monitoring to detect intracranial hypertension. Adv Biomed Res. 2005 Oct 22;4:231.

Type of Study: cross-sectional case-control
Objective: To determine whether transocular Doppler and ONSD monitoring could reliably identify increases in ICP
Results: mean ONSD of 4.8 mm in patient with raised ICP vs 3.2 mm in healthy volunteers
Conclusion: US as alternative safe technique to invasive ICP methods

 

How to Perform the Ultrasound
  1. Use the high-frequency linear transducer.
  2. Cover the closed eyelids with a tegaderm and apply ultrasound gel.
  3. Have the patient stare straight ahead without squinting.
  4. Adjust the depth so that the eye fits within the entire screen.

eye in screen
http://sinaiem.us/education/papilledema-and-the-crescent-sign

  1. Measure the optic nerve sheath diameter at a distance 3 mm posterior to the globe, where the US contrast is greatest.

ONSD diagramhttp://sinaiem.us/education/papilledema-and-the-crescent-sign

 

ONSD 2

ONSD 4

ONSD 5

  1. Measure the ONSD twice. Determine the average.
  2. An ONSD > 5 mm suggests elevated intracranial pressure.

The optic nerve sheath contains fluid in which sits the optic nerve. The sheath attaches to the posterior aspect of the globe and is contiguous with the subarachnoid space. Accordingly, the ONSD can act as a surrogate for intracranial pressure.

 

Other References

http://www.criticalcarehorizons.com/optic-nerve-sheath-diameter-icp/
http://www.ncbi.nlm.nih.gov/pubmed/25595270
http://www.ncbi.nlm.nih.gov/pubmed/25497897
http://www.ncbi.nlm.nih.gov/pubmed/25284485

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