A 28-year-old obese woman comes into your ED complaining of 4 days of throbbing, global intermittent headache. It is more severe than previous headaches she has had. The headache is associated with retrobulbar pain and transient loss of vision lasting seconds. The visual symptoms are exacerbated by standing. She denies fevers, chills, confusion, neck pain or stiffness.
She is afebrile, and the rest of her vitals are unremarkable.
You perform a full neurological and visual acuity/field exams. She is intact on exam except she has some mild deficits in all visual fields, with normal visual acuity.**
Suspecting Idiopathic Intracranial Hypertension (IIH; also known as pseudotumor cerebri), you quickly perform a fundoscopic exam.
** Note that in IIH the visual presentations are highly variable, with visual field testing considered more sensitive for detecting optic nerve damage in the early stages; deficits in visual acuity are considered a later finding. *(8) The deficits in visual field testing can also be variable with possible deficits in all quadrants or in some of the quadrants.You grab the ophthalmoscope in the room and what you see is…
…Part of the patient’s eyelashes and some vessels. You notice the patient feeling a bit uncomfortable as you are shoving your face millimeters from hers, trying to find this fabled papilledema.
As you walk back towards your attending, a dangling object with jelly and some other questionable material hits your hand.
Gross…but wait… what’s this?
It’s the mythical ultrasound machine… the stuff of EM legend… our sword in the stone… our Excalibur.
You quickly wash Excalibur, I mean the ultrasound probes, with some towels and the sterile cleaning spray and march towards the patient like a King, or Queen, or whatever makes you feel like a boss.
You remember learning from Merlin, I mean your ultrasound faculty, that there are ways of finding images suggestive of increased intracranial pressure (ICP) and papilledema with the ultrasound machine by measuring the optic nerve sheath diameter (ONSD).
How is this done?
Step 1. Clean the probe. Always clean the probe, c’mon!
Step 2. Make sure your machine is plugged in to a socket. You don’t want that awkward interval where the machine suddenly turns off in the middle of your exam.
Step 3. Use the linear probe, you know, the flat one.
Step 4. Have the patient close her eyes.
Step 5. Place a Tegaderm over the patient’s eyes.
Step 6. Put as much gel as you can balance on top of the patients eyelid.
Step 7. Instruct the patient to stare straight ahead
Step 8. Place the probe on top of the patient’s closed upper eye lid. Adjust the depth so the eye fits in your screen*(1, 2)
So what are you looking for?
Identify the optic nerve sheath, which will appear as a hypoechoic extension of the retrobulbar portion of the eye. To measure the ONSD, measure the width of the optic nerve sheath at 3 mm (0.3 cm) behind the papilla.*(1) Measure both eyes. If their average width is > 5 mm, this is suggestive of increased ICP and may correlate with an intracranial pressure greater than 20 cm H2O. *(3)
In severe cases, you might see the “Crescent Sign,” which appears an echolucent circle within the optic nerve sheath.*(4)
There are also case reports of optic disc bulging into the posterior chamber on ultrasound, which may correlate with the physical exam finding of papilledema. *(5,6,7)
Why do you see these findings on ultrasound in elevated intracranial pressure?
CSF runs through the optic sheath and surrounds the optic nerve. Back to your patient…As suspected, the ONSD measures >5 mm.
The patient undergoes a CT to make sure there is no mass causing these findings. The CT is unremarkable.
You perform an lumbar puncture (LP).
The opening pressure is 38 cm H2O. There is no recommended minimum amount of CSF to drain. LPs, specifically serial LPs, were used in the past as treatment to alleviate the headaches, however LPs are now only considered for diagnostic purposes or as temporizing measure for more aggressive surgical treatments in those refractory to maximum medical treatment. LP can still be used as temporizing treatments in special situations, such as in pregnant women in which medications might be contraindicated or in cases of rapidly declining vision as a bridge to surgical treatment. *(8) A diagnostic opening pressure is greater than 25 cm; 20-25 cm is equivocal; while an opening pressure less than 20 cm is considered normal. *(8)
Her headaches and visual symptoms improve after the LP. She is admitted to Neurology, and the neurologists ultimately agree with your diagnosis. She is discharged on acetazolamide and follows up in neurology clinic as an outpatient. It was important to make this diagnosis because if left untreated, the visual symptoms, including visual loss, can become permanent.
How effective is ultrasound at finding sign of increased intracranial pressure?
In one study, 26 patients with known IIH were placed in Group A, while 26 healthy controls were placed into Group B. Mean ONSD for Group A was 6.61 mm+ 0.39mm, while in Group B the mean was 4.33 + 0.38mm (p<0.001).*(9)
In another study of 38 ocular ultrasounds in 15 patients (4 with TBI, 11 with spontaneous ICH) with invasive intracranial monitoring for ICP measurement (EVD) in the ED and ICU, the ONSD cutoff of 5.0 mm revealed a sensitivity of 88% (95% CI=47-99%) and specificity of 93% (95% CI= 78-99%) for ICP >20mm Hg. *(3)
Yet, in another study (n= 59), 8 patients had CT findings of increased ICP and a mean binocular ONSD of 6.27 mm on ultrasound, while the other 51 without CT findings of increased ICP had a mean binocular ONSD of 4.94 mm on ultrasound. Using the 5.0 mm OSND cutoff, this corresponded to a sensitivity of 100%(95 % CI= 68-100%) and a specificity of 63% (95 % CI=50-76%) of bedside ultrasound to detect increased ICP using CT findings as the standard. *(10) Note that for both of these studies the study population did not have IIH.
So what are we to conclude about bedside ultrasound to detect increased intracranial pressure in those with suspect with IIH?
Unfortunately, all of these studies have limited power, and further research is needed. But, it is possible that a ONSD cutoff of 5.0 mm may be sensitive to detect an intracranial pressure of >20 mm Hg, with higher measurements perhaps yielding higher specificity. Optic disc bulging and the crescent sign may also be helpful ultrasound findings. Such findings are going to be dependent on your experience with ultrasound. The results of these studies are limited because of their small sample size; however, ultrasound can be used as an adjunct that may influence your clinical suspicion for IIH, especially when the fundoscopic exam is limited. While ultrasound cannot currently replace LP for diagnosis, it is a noninvasive tool to assess for possible increased ICP.
*1. Jochen Bäuerle∗ , Max Nedelmann. B-mode sonography of the optic nerve in neurological disorders with altered intracranial pressure. Department of Neurology, Justus-Liebig-University, Giessen, Germany. Perspectives in Medicine (2012) 1, 404—407
*2. Stephen Alerhand, MD Edited by: Alex Koyfman, MD. Ultrasound for Optic Nerve Sheath Diameter. DEC 30TH, 2015. http://www.emdocs.net/ultrasound-for-optic-nerve-sheath-diameter/
*3. Kimberly H.H., Shah S., Marill K., Noble V. Correlation of optic nerve sheath diameter with direct measurement of intracranial pressure. Acad Emerg Med, 15 (2) (2008), pp. 201-204
*4. Marchese RF1, Mistry RD, Scarfone RJ, Chen AE. Identification of optic disc elevation and the crescent sign using point-of-care ocular ultrasound in children. Pediatr Emerg Care. 2015 Apr;31(4):304-7.
*6. Nathan Teismann, MD, Patrick Lenaghan, MD, Rachel Nolan, John Stein, MD, and Ari Green, MD Point-of-care Ocular Ultrasound to Detect Optic Disc Swelling. ACADEMIC EMERGENCY MEDICINE 2013; 20:920–925
*7. Daulaire S., Fine L., Salmon M., et al. Ultrasound assessment of optic disc edema in patients with headache. American Journal of Emergency Medicine. 2012;30(8):1654.e1–1654.e4. doi: 10.1016/j.ajem.2011.06.030.
*8. Friedman, Deborah I. MD; Jacobson, Daniel M. MD. Idiopathic Intracranial Hypertension. Journal of Neuro-Ophthalmology. Issue: Volume 24(2), June 2004, pp 138-145
*9. Rehman H1, Khan MS2, Nafees M1, Rehman AU1, Habib A2 Optic Nerve Sheath Diameter on Sonography in Idiopathic Intracranial Hypertension Versus Normal. J Coll Physicians Surg Pak. 2016 Sep;26(9):758-60. doi: 2430.
*10. 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.
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.
B-mode sonography of the optic nerve in neurological disorders with altered intracranial pressure Jochen Bäuerle∗ , Max Nedelmann Department of Neurology, Justus-Liebig-University, Giessen, Germany. Perspectives in Medicine (2012) 1, 404—407
Stone M. B. Ultrasound diagnosis of papilledema and increased intracranial pressure in pseudotumor cerebri. The American Journal of Emergency Medicine. 2009;27(3):376.e1–376.e2. doi: 10.1016/j.ajem.2008.08.007.
Point-of-care Ocular Ultrasound to Detect Optic Disc Swelling Nathan Teismann, MD, Patrick Lenaghan, MD, Rachel Nolan, John Stein, MD, and Ari Green, MD
ACADEMIC EMERGENCY MEDICINE 2013; 20:920–925
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