US Journal Club November, 2019: Ocular Ultrasound

Paper 1

Optic nerve ultrasound for the detection of elevated intracranial pressure in the hypertensive patient

Roque, P.J. et al. Annals of Emergency Medicine, Volume 58, Issue 4. doi:10.1016/j.ajem.2011.09.025

Full Text

  • Background information
    • Malignant hypertension is defined as a blood pressure >180/120 with signs of end-organ dysfunction. These patients require rapid blood pressure control.
    • In patients with acute intracranial hypertension, determination of the intracranial pressure (ICP) can be difficult. Traditional fundoscopic examination for papilledema only yields a sensitivity and specificity of 20 – 30% and can be delayed by hours in its appearance1-2.
    • A non-invasive method involves measurement of the optic nerve sheath diameter (ONSD) given that pressure variations within the brain are transmitted to the surrounding tissues of the optic nerve. 
    • Bedside ultrasound in the ED can be used to measure the ONSD. A level above 5 mm correlates with increased ICP with sensitivity of 88% and a specificity of 93%1.   
  • What was the objective of this study?
    • To determine whether elevated ONSD, measured by bedside US, correlates with patient’s blood pressure along with determination if there was a blood pressure cutoff at which an abnormal dilation of the ONSD would be seen.
  • Methods and study design
    • Prospective observational trial using a convenience sample of patients presenting to an urban ED (Level 1 trauma center with 60,000 patients per year)
    • 150 patients enrolled
    • 3 study arms (50 patients per arm)
      • Normotensive and asymptomatic (control arm)
      • Hypertensive and asymptomatic
      • Hypertensive and symptomatic
    • Hypertension was defined as SBP ≥140 OR DBP ≥90 mm Hg
    • “Symptomatic” was defined as complaints including:
      • Headache, diplopia or blurry vision
      • Chest pain or SOB
      • Dizziness or vertigo
      • Nausea or vomiting
      • Abdominal or extremity pain
      • Weakness
    • Exclusion criteria:
      • Age <18 years age
      • Incarcerated
      • Unable to consent
      • Unstable
      • Normotensive and symptomatic patients
    • Patients in hypertensive/symptomatic group underwent ONSD measurement before and 20 minutes after BP treatment (11 total were treated)
    • Ultrasounds performed by both residents and attendings after attending a 2 hour lecture + hands on session on ocular US
    • All patients were in supine position for the US
    • Final ONSD was from an average of 4 measurements (2 per eye, one in sagittal and one in transverse plane) with ≥5 mm being abnormal 
  • What was the primary outcome?
    • Correlation of bedside ultrasound measurement ONSD with blood pressure.
  • Discussion
    • The use of US for determining elevations of ICP can potentially spare patients radiation from head CTs
    • Out of all symptoms, only blurry vision was associated with abnormal ONSD
    • SBP was found to be the most closely associated with ONSD (correlation 0.396)
    • Authors suggest patients with BPs of ≥166/82 should be managed more aggressively 
  • Were there any limitations?
    • All US were performed by residents or EPs with 2 hour training session, potentially limiting generalizability
    • No imaging control group existed (CT or MRI)
    • Small sample size as only a total of 11 patients underwent treatment for BP
    • Poor correlation coefficient for SBP to abnormal ONSD
  • Take home points
    • Ocular US provides a rapid, non-invasive and repeatable method for determining ONSD compared to fundoscopy or CT scan
    • This study found correlation (although weakly) between a hypertensive patient’s ONSD on bedside US with their blood pressure, especially in those presenting with blurry vision
    • Authors suggest using a blood pressure cut-off in a symptomatic patient of ≥166/82 to more aggressively treat
    • Larger, randomized controlled studies with standard imaging control groups are needed in the future to determine use in clinical practice

Sources

  1. Kimberly, H. H., Shah, S. , Marill, K. and Noble, V. (2008), Correlation of Optic Nerve Sheath Diameter with Direct Measurement of Intracranial Pressure. Academic Emergency Medicine, 15: 201-204. doi:10.1111/j.1553-2712.2007.00031.x
  2. Trobe JD. Papilledema: the vexing issues. J Neuroophthalmol 2011;31(2):175-86.

Paper 2

Point-of-care ultrasound for the evaluation of non-traumatic visual disturbances in the emergency department: The VIGMO protocol

Gandhi, K. et al. The American Journal of Emergency Medicine, Volume 37, Issue 8. https://doi.org/10.1016/j.ajem.2019.04.049.

Full Text

  • Background information
    • Patients presenting to the ED with non-traumatic eye complaints can be difficult due to challenging high-quality fundoscopic exams, inability to perform pupillary dilation and the risk of unnecessary consultation/transfers to outside centers for further workup.
    • Bedside ocular ultrasound can augment evaluation in these cases and has been shown to be reliable for assessment of acute, non-traumatic vision threats1-2
  • Protocol
    • The authors propose a protocol with the acronym ViGMO for patients presenting with acute, monocular, painless, non-traumatic visual disturbances (including flashers, floaters, visual field cuts, blurry vision):
      • Are there any abnormal findings noted within in the Vitreous?
      • Is there any change with high or low Gain settings?
      • Is there any change with eye Movement?
      • What is the appearance of the Optic disc itself and the anatomic relationship of the disc to any abnormal findings within the vitreous? 
    • Binocular visual deficits are more likely to be CNS in etiology and complete vision loss is more likely from a vascular process (such as central retinal vein/artery occlusion) neither of which can be reliably diagnosed with the ViGMO protocol.
  • Four major diagnoses to consider
    • Vitreous syneresis 
      • The most common cause of floaters; a common, degenerative and benign process in which the fluid portion of the vitreous separates out into “lakes” leading to visual disturbances
    • Posterior vitreous detachment 
      • Another cause of floaters, but also age-related and benign
      • Rarely the retina can detach along with the posterior vitreous layer
    • Retinal detachment
      • Vision threatening condition when retina separates from posterior epithelium
    • Vitreous hemorrhage
      • May present with cloudy or smoky vision to complete vision loss
      • More commonly seen in diabetics or those on anticoagulation
  • Findings on ocular ultrasound
    • Patient in supine position with use of high frequency linear transducer
    • Vitreous Syneresis
      • Appears as small, flat, reflective and highly mobile surfaces which may be connected by a web-like network
      • Become more apparent at high gain settings
      • With eye movement are very mobile and show “aftermovement”
    • Posterior vitreous detachment (PVD)
      • Appears as single, thin and slightly curved membrane with low to medium reflectivity, “floating” just above and parallel to retina and not attached to optic disc
      • Subtle at low gain, so need to increase gain to ensure full visualization
      • Will sway significantly with eye movements and will “lag” behind glove movements
    • Retinal detachment (RD)
      • Thick, smooth, highly reflective and “rope” appearing structure anchored to the optic disc
      • Should be seen in both low and high gain settings
      • With movement the RD will show restricted aftermovement, like a “taught bedsheet” unlike the freelowing movement in a PVD
    • Vitreous hemorrhage (VH)
      • Appears as diffuse, low level echo textures in the vitreous reminiscent of a “snow-globe”
      • As it settles can mimic RD but can be distinguished as VH will have a more irregular and “crinkly” appearance unlike the smooth texture in RD
      • Can be seen in normal gain settings
    • Optic disc edema
      • Optic disc should appear flat
      • Normal measurement of anterior peak of optic disc to intersection of posterior surface of globe is normally less than 0.6 mm and typically represents edema if over 1 mm
  • Take home points
    • Emergency ocular ultrasound provides a promising supplement to an otherwise difficult physical examination of the eye
    • The proposed ViGMO protocol involves investigating the vitreous, noting changes with gain or eye movement and anatomic relationships with the optic disc to identify vision threatening pathology

Sources

  1. Yoonessi R, Hussain A, Jang TB. Bedside ocular ultrasound for the detection of retinal detachment in the emergency department. Acad Emerg Med 2010;17(9):913–7 Sep.
  2. Blaivas M, Theodoro D, Sierzenski PR. A study of bedside ocular ultrasonography in the emergency department. Acad Emerg Med 2002 Aug;9(8):791–9.

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