VOTW: I'd Tap That

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Case 1: A 69 yoF with a PMHx of osteoarthritis presented to the ED with 1 day of worsening knee pain. The workup revealed a moderate-sized effusion and elevated CRP. These factors, combined with her discomfort, prompted the providers to perform an arthrocentesis.

Approach: While there are many approaches you can take to tap a knee effusion, the one I have seen most often is the suprapatellar approach (note: it is best to identify the area with the biggest pocket). Next, gather your equipment for a regular arthrocentesis plus a probe cover. Once you identify your pocket, turn your probe so it is in-plane with your needle. Advance your needle until you see it enter your fluid pocket and aspirate. Remember to put color flow over the expected trajectory of your needle to avoid vasculature.

Image 1: Knee arthrocentesis set-up

  • Video 1 shows the moderate-sized effusion in the suprapatellar region. (note: you can also see a separate, rounded, fluid-filled area, which is the pre-patellar bursae).

  • Video 2 shows the needle in-plane during active aspiration.

  • Video 3 shows the needle in the decompressed joint space.

Case 2: A 102 yoF came to the ED with difficulty ambulating due to ankle pain. On exam, she had swelling, tenderness, and pain with passive/active range of motion. Bedside US showed a joint effusion and inflammatory markers were elevated. In conjunction with the family, the decision was made to tap the ankle joint.

Image 2: normal tibiotalar joint space

Image 3: tibiotalar joint space with effusion

Video 4 shows a fluid collection at the tibiotalar joint. 

Video 5 shows Dr. Tran performing a dynamic aspiration of the ankle effusion.

Results: Results from the arthrocentesis in case 1 showed inflammatory arthritis and case 2 was gout. While neither case turned out to be septic arthritis, both patients felt much better after the tap and were able to ambulate. 

Why use ultrasound? Using ultrasound guidance to perform an arthrocentesis allows you to see the exact location of the joint effusion, improving your first-pass success rate. In addition, using color-doppler before the tap decreases the risk of neurovascular injury.

References:

https://coreultrasound.com/knee-aspiration-and-injection/

https://cdn.mdedge.com/files/s3fs-public/Document/June-2017/em049070329.PDF

https://www.tamingthesru.com/blog/mastering-minor-care/ankle-arthrocentesis

Happy scanning! 

Ariella Cohen M.D.

VOTW: Idiopathic Intracranial Hypertension

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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:

  1. Use a linear probe

  2. Use a lot of gel over a closed eye lid

  3. Find the hypoechoic optic nerve and the more echogenic nerve sheath surrounding the nerve

  4. 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:

  1. Shevlin, C. (2015). Optic nerve sheath ultrasound for the bedside diagnosis of intracranial hypertension: pitfalls and potential. Critical Care Horizons, 1(1), 22-30.

  2. 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!! 🙌

VOTW: Twinkle Artifact

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This week's VOTW is brought to you by Dr. Sanghvi and the UST!

An 80 year old male w/ hx of CVA, non-verbal, PEG dependence, hx urosepsis presented from a nursing home w/ hypotension and “rule out sepsis”. Given the broad differential, the UST performed multiple scans including aorta, echo, chest, FAST, renal and bladder. The left kidney showed hydronephrosis and a POCUS of the bladder was performed which showed...

Clip 1 shows a transverse view of the bladder w/ color doppler placed over the L ureterovesicular (UVJ) junction demonstrating “twinkle artifact” 🌟. This indicates the presence of a stone!

The stone can also be seen without color doppler in clip 2 as a hyperechoic structure with posterior acoustic shadowing. It is associated with upstream hydroureter which can be seen as the clip fans thru. The rectum posteriorly is also distended and filled w/ stool.

Twinkle Artifact

Twinkle artifact

While we often only find indirect signs for ureteral stones on POCUS (hydronephrosis/hydroureter), you might sometimes be able to find the culprit stone on your bladder views. They are easy to miss since the bladder wall is also echogenic, especially if the stone is small. This is where twinkle artifact can be useful!!

When color doppler is used over a rough, hyperechoic, irregular object like a stone, the ultrasound waves get reflected internally within the stone, tricking the machine into thinking that there is movement, resulting in the stone being highlighted by a rainbow doppler signal. Sometimes it will have a rainbow tail extending away from the probe.

The presence of twinkle artifact has a high positive predictive value for the presence of kidney stone (1) and is more sensitive for detection of small stones than is acoustic shadowing (2).

Back to the patient

A CTAP showed three obstructing L ureteral stones, largest being 9mm. Urology was consulted and patient underwent L ureteral stent placement with findings of “pus behind left ureteral stone”. The patient was admitted to the MICU for septic shock.

References

  1. Dillman J, Kappil M, Weadock W et al. Sonographic Twinkling Artifact for Renal Calculus Detection: Correlation with CT. Radiology. 2011;259(3):911-6. doi:10.1148/radiol.11102128 

  2. Hosn S, Rutten C, Murphy A, et al. Twinkling artifact. Reference article, Radiopaedia.org (Accessed on 20 Feb 2024) https://doi.org/10.53347/rID-21828