Hi all,
This week’s VOTW was a case from several months ago brought to you by future ultrasound fellow Dr. Jennie Xu!
A 23 year old female w/ hx of migraines was referred to the ED by an ophthalmologist for 4 weeks of intractable headache and three days of vomiting and vision changes. The patient was told she had a "pinched nerve in her eye". She was seen in another ED 1 week ago with a normal head CT. She had no focal deficits on exam. An ocular POCUS was performed which showed…
Clip 1 shows a fan thru of a normal appearing globe. Posterior to the eye, an edematous optic nerve sheath is seen. The optic nerve sheath diameter (ONSD) measured 0.65cm on the right and 0.68cm on the left. The optic disc also appears to be elevated. This is concerning for sonographic papilledema.
Given the concern for intracranial hypertension, a lumbar puncture was performed with an opening pressure > 50mmHg (the CSF actually spouted over the top of the measuring column like a water fountain ⛲).
Optic nerve sheath diameter (ONSD)
The optic nerve sheath communicates directly with the intracranial space. For the few of us that are not great at the fundoscopic exam, measuring the ONSD might be an easier alternative to evaluate for papilledema (but see test characteristics below).
How to:
Use a linear probe
Use a lot of gel over a closed eye lid
Find the hypoechoic optic nerve and the more echogenic nerve sheath surrounding the nerve
Measure the entire sheath from outer edge to outer edge at a depth of 3mm posterior to the globe (see image above)
Measurements
< 5mm is normal
5 – 6mm is a grey zone
>6mm is abnormal
Evidence
These cutoffs have a sensitivity 88-100%, specificity 63-95% for papilledema (1). The problem is many patients end up in the 'grey zone'.
*A normal ONSD does not necessarily indicate normal intracranial pressure (ICP). A dilated ONSD might also be normal for that patient, so correlate clinically!
**ONSD unfortunately can't be used to estimate a specific ICP.
So the next time you find yourself wanting to do a fundoscopic exam, whip out your probe instead! (or use the new retinal camera in fast track...)
Back to the patient
Neurology was consulted, the patient was started on acetazolamide, and admitted to medicine. Interestingly, her CSF VZV PCR was positive so she was diagnosed with VZV meningitis. She was started on antivirals and did well overall. Her vision problems and headaches improved.
References:
Shevlin, C. (2015). Optic nerve sheath ultrasound for the bedside diagnosis of intracranial hypertension: pitfalls and potential. Critical Care Horizons, 1(1), 22-30.
Farkas, J. (2017). PulmCrit: Algorithm for diagnosing ICP elevation with ocular sonography. (https://emcrit.org/pulmcrit/pulmcrit-algorithm-diagnosing-icp-elevation-ocular-sonography/)
This is my last post as your ultrasound education fellow 😢. If you've read this far, I appreciate you! Thanks Dr. Danta for coming up with most of my titles ha ha ha... Dr. Ariella Cohen will take us thru the home stretch!! 🙌