Consider the Probe

CONSIDER THE PROBE: CASE 2


49 y/o M with hx of HTN, HLD, IDDM presents with non-traumatic L-sided painless visual loss.  The patient states that several hours prior to presentation he developed blurry vision in his L eye.  On quick examination, there are no signs of trauma.  Visual acuity is 20/120 on the L and 20/40 on the R with normal intraocular pressures bilaterally.  Pupils are briskly reactive without any photophobia or consensual photophobia.  The lids, sclera, conjunctivae are grossly normal and there are no corneal defects with fluorescein staining. 


Coming out of the room, you are concerned about this sudden-onset blurry vision.  You remember a short lecture on visual acuity changes that Dr. Schindlebeck begrudgingly gave you in between his posting about sweater vests on Pinterest.  Your differential brings concerning diagnoses including central retinal arterial occlusion (CRAO), central retinal vein occlusion (CRVO), retinal detachment, as well as vitreous hemorrhage.  Now, our patient still has some visual acuity in the affected eye which speaks against CRAO (usually profound loss of visual acuity…unable to count fingers, etc.).  CRVO is certainly on the differential, but it is usually not a time-sensitive diagnosis to make.  That leaves us with retinal detachment vs vitreous hemorrhage.  Might be a nice time to CONSIDER THE PROBE!

Brushing up on the basics, ocular US is performed utilizing the high frequency linear probe. ALWAYS make sure you clean the probe prior to examination and use sterile gel packets.  You can consider placing a tegaderm over the closed eye to further protect it.  Fear not, you will not remove their eye-lashes when ripping the teggy off.  Finally, make sure to “brace” your hand on the bridge of the nose or the cheek as to avoid applying too much pressure to your patient’s globe.  Using plenty of gel, minimal pressure is needed to visualize both superficial structures (cornea, iris, lens) as well as the posterior chamber as shown below:

 (http://www.sonomojo.org/keeping-an-eye-on-intracranial-pressure-detecting-elevated-icp-using-ocular-ultrasound)


It sure beats your non-dilated funduscopic exam.  Anyways, let’s say you place the probe over your patient’s affected eye and ascertain the following image:

                                          
https://i.ytimg.com/vi/KZIK2-t9jpw/hqdefault.jpg




Noting the echogenic (hyperechoic) snake-like structure floating in the vitreous that ORIGINATES from the optic nerve (the optic nerve sheath is the hypoechoic “band” passing posteriorly from the vitreous chamber, see image above for anatomy review)—you are appropriately concerned that your patient may have a retinal detachment and needs urgent ophthalmologic consultation and you put a page out to the on-call resident.

Lets imagine that your bedside ultrasound of the affected eye had produced the following images/videos:


You note more globular hyperechoic material that swirls with kinetic maneuvers.  There is no “connection” to where the optic nerve originates.  Thus, you are less concerned for a retinal detachment and are moving towards a less time-sensitive diagnosis of vitreous hemorrhage.  Recognize that sometimes these hemorrhages can be subtle and may require you to adjust your gain (“lighten” your image) to visualize the abnormality.  While you still want to provide your patient with a prompt ophthalmology f/u appointment, you recognize that you probably don’t need to page the on-call consultant at 3:30 in the morning for a patient with these findings.  

Take it to the next level:


Like all things, Ocular US takes practice.  Fortunately, at Cook County we have an abundance of visual acuity complaints.  If you start imaging all of these patients early on, you will develop a good “eye” for normal vs abnormal findings.  One “next-level” step to ocular ultrasound involved further interpreting a patient with findings concerning for a retinal detachment to determine whether the macula is involved.  It is important to remember that the macula is the part of the retina responsible for “high-acuity” and central vision.  So retinal detachments can either involve this important region termed “Mac-Off” (macula detached) or they can spare it “Mac-On.”  To assess this, you must be able to localize the macula—it is immediately lateral to the optic nerve and usually inline with the middle of the lens (direct line of vision):

(https://www.ultrasoundoftheweek.com/uotw-12-answer)


Now on account of the critical role the macula fulfills, any retinal detachment that spares the macula “Mac-On” requires EMERGENT optho consultation (that’s right, pick up the phone at 4AM…).  While patients that have already detached this region “Mac-Off” patients are slightly less time-sensitive and require URGENT follow-up.  The subtle difference between these findings is noted in the images below:


“Take Home Pearls”


1) Retinal Detachments appear as a snake-like hyperechoic extension floating in the vitreous that should “originate” from the optic nerve.

2) Vitreous hemorrhage appears as less well-defined hyperechoic “globular” debris in the posterior chamber.  It may be subtle and you may have to adjust the gain to visualize it. 

3) Retinal detachments that preserve the macula “Mac- On” require EMERGENT ophthalmologic consultation, while “Mac-Off” detachments are URGENT, but non-EMERGENT. 

Sources/Links: 


5 Min Sono Video Retinal Detachment vs Vitreous Hemorrhagehttp://5minsono.com/rdvd/

Chapter 31 on Introduction to Clinical Ultrasound by Matt Dawson and Mike Mallin.  Still appears to be free on Itunes.  (https://itunes.apple.com/us/book/introduction-to-bedside-ultrasound/id554196012?mt=11)

Random Youtube Video with nice example of “Mac-On” vs Mac-Off” detachment: https://www.youtube.com/watch?v=JijIfSzOG9U


CONSIDER THE PROBE: CASE 1


Case 1: 29 y/o M with hx of asthma, nephrolithiasis presents with R sided flank-pain x 2 days.  Pt denies gross hematuria, but describes a colicky pain that radiates to his groin. He is afebrile, but tachycardic and uncomfortable.  UA shows 40-50 rbcs/hpf, < 5wbcs/hpf.  Pt states that he had a prior kidney stone, but it was on his L side and he had grossly bloody urine at that time.  The patient’s abdomen is soft, nontender.  CBC shows no leukocytosis, no shift, BMP with normal creatinine.  What’s your next move?

Well…if it’s the oral boards, you order weight-based morphine at 0.1mg/kg and shortly afterwards, the patient becomes apneic.  In the real world why don’t we give a 1L NS bolus, some Tordol (maybe at the reduced dose of 15mg IV per the recent literature) and then CONSIDER THE PROBE! 

While US is poorly sensitive for visualizing stones themselves, it has a relatively high sensitivity for detecting hydronephrosis (up to 98%, Tintanellis and other sources below).  Hydronephrosis describes a dilatation of the calyceal system with urine, due to downstream obstruction (stone, or maybe just anatomical).  It is categorized as mild-moderate-severe (see Introduction to Bedside US Ch. 6 for definitions of each category, really takes practice by looking at images.) 

The degree of hydronephrosis is related proportionally to renal stone size.  Just to recall: stone < 5mm passes spontaneously 97%, while stone > 7mm only passes 39% (Gospel of Tintanelli.) Therefore, patients with a typical presentation of nephrolithiasis without moderate-severe hydronephrosis on POCUS have a high likelihood of passing their stone spontaneously and a low likelihood of requiring any surgical intervention.  Great news!  You may be able to save your patient a CT scan saving them not only radiation but making their ER trip cheaper (good for them) and shorter (good for us). 

There is even evidence to support this practice (check out Dr. Bailitz’s article Ultrasonography vs Computed Tomography for Suspected Nephrolithiasis in NEJM, we won’t delve into it now, but worthy of a read: http://www.nejm.org/doi/full/10.1056/NEJMoa1404446#t=article). 

Utilizing the Curvilineal Probe on Renal settings you scan the patient’s R and L kidneys making sure to visualize them completely in both short and long axis.  You see these images:


R Kidney:



L Kidney:



You correctly note only mild hydronephrosis on the right.  With a benign abdominal exam and a UA supportive of your diagnosis, you confidently diagnose the patient with R sided nephrolithiasis and write the patient for some analgesics, encourage hydration, consider tamsulosin (a separate evidence-based discussion) and instruct the patient on proper return precautions. 

What if our bedside US had showed this image of the R kidney?




You correctly note the “bear-claw” pattern on the R showing moderate to severe hydronephrosis.  Correctly recognizing the patient’s higher risk for having either a larger obstructing stone or structural abnormality (malignancy!), you decide to either perform a CT scan at this time or consult directly with Urology. 

“Take Home Pearls”


1) Give a fluid bolus prior to Bedside US as it will improve the sensitivity of your exam to detect hydronephrosis. (In volume deplete patients, there may be a lack of “build-up”)

2) POCUS should be your initial imaging study when you are evaluating a patient with a typical presentation of nephrolithiasis.  However, in a febrile/septic/toxic appearing patient remember to consider complications such as an infected stone or a renal abscess that may require CT for diagnosis and operative planning. 

3)In patients with absent or mild hydronephrosis, consider “treating” the patient for nephrolithiasis without further imaging or consultation.  While patients with moderate-severe hydronephrosis, require further imaging (CT) or consultation with Urology, as these patients are likely to require operative intervention. 

4)After scanning the kidneys, make sure to check out the aorta, to r/o pathology (AAA, dissection)—especially in older patients with risk factors (smoking, HTN, talk to a fourth year medical student…)

Thanks for reading and always remember when you are on shift to always remember to CONSIDER THE PROBE!

Sources/Links


Chapter 6 on Introduction to Clinical Ultrasound by Matt Dawson and Mike Mallin.  Still appears to be free on Itunes.  (https://itunes.apple.com/us/book/introduction-to-bedside-ultrasound/id554196012?mt=11)

Nice videocast from the US podcast website: (http://www.ultrasoundpodcast.com/2012/05/episode-27-renal-ultrasound/ )