Feet: The Next Frontier for Emergency Ultrasound

Soundings

What do you see? Should you stick a needle in any of these?

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It’s the middle of a slow weekend shift in the rural ED where you work when a 72-year-old female patient with a history of hypertension comes in complaining of pain and redness on the dorsum her left foot. The pain started “without warning” about 36 hours ago and isn’t getting any better. It seemed like it got really bad within 6-12 hours of onset then sort of hit a plateau. There was no injury, so she thought it was going to get better, but unfortunately it hasn’t. She says the pain makes it hard to walk and she can’t wear her regular shoes. There has been no fever, trauma or other complaints. She has no prior history of a similar condition, and other than hypertension, her past medical history is unremarkable. Her medications include atenolol, hydrochlorothiazide and baby aspirin.

On exam, your patient appears to be in mild distress. Her vital signs are normal except for a blood pressure of 172/86. An examination of the head and neck is normal except for a few whitish lumps on both ears, which she says have been there “for years”. The lungs are clear and the heart is regular with a soft systolic ejection murmur. Her extremities are normal except for the feet. The skin is intact and the pulses are strong, but the dorsum of the left foot is definitely red, slightly swollen and tender. Although the area is red, it is not really that much warmer than the other side and motion of the foot and toes seems to aggravate the pain a lot more than palpation.

While you are examining the left foot, your patient says, “while you’re checking my feet, can you take a look at my right foot too. I have two lumps, one on the top and one on the bottom that I’ve been meaning to have checked out.” On the dorsum of the painless foot toward the toes there is a non-tender mobile cluster of nodules, each about 1 cm in size, and on the plantar surface there is a fullness and possible deep seated mass that has too much overlying structure to really palpate well.

Given her age, the atraumatic onset of redness and pain without much in the way of localized warmth or fever, the rapid peak of symptoms in a way that would be atypical for an infection, and the lesions in her ears that look like gouty tophi, you suspect your patient may be suffering her first clinical attack of gout. Your suspicion is heightened when you learn that she recently started taking hydrocholorothiazide; a medication known to precipitate an attack of gout. You would like to confirm the diagnosis by aspirating some uric acid crystals, but the area of her foot that is symptomatic is not at a joint. Knowing that gout can affect tendons as well, you wonder if she’s developed a fluid collection around her tendon that is amenable to aspiration.

A few minutes later you find the time to scan the dorsum of her left foot, and while you’re at it, you take a look at the other foot where she has the chronic asymptomatic “lumps”.

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You obtain images 1, 2 and 3. What do you see? Should you stick a needle in any of these?

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Image 1 shows a transverse view of the extensor tendon of the third toe surrounded by a halo of fluid. The tendon appears as a hyperechoic disc with an abnormal collection of anechoic fluid surrounding it. You can use ultrasound to help guide the aspiration which would clinch your diagnosis of gout.
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Image 2 shows a multiloculated ganglion cyst filled with anechoic fluid. Deep to this you can see the hyperechoic superior surfaces of the metatarsal bones and posterior shadowing deep to that. If you tap this, you would expect to obtain a clear gel. If you do, send the fluid to pathology, but since it’s not an emergency, it’s probably best to turf this to a dermatologist or a surgeon.
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Image 3 of the plantar area shows a hypoechoic oval mass (light gray) that lies within the plantar fascia and is most consistent with a plantar fibroma. Deep to this mass, running at a slight angle from horizontal, you can see the slightly hyperechoic fibers of a digital flexor tendon. In real time, you could see this tendon move if you ask the patient to flex and extend her toes.
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After obtaining informed consent for the procedure, you prep and drape the foot in a sterile fashion. Aspiration of the fluid from around the extensor tendon is sent to the lab and comes back positive for negatively birefringent crystals and negative for any bacteria. You decide to start her on prednisone (or an NSAID) and Percocet and about an hour after the first dose of both of these, she is able to ambulate fairly well with the help of a cane. It’s homeward bound for her and in about 4 more hours it will be homeward bound for you too.

Pearls & Pitfalls: Musculoskeletal Ultrasound

Know your limitations
Ultrasound may help clarify findings elicited by a thorough history and physical exam. When used correctly, it can greatly improve diagnostic accuracy, and help guide patient management, especially for time-critical diagnosis and treatment of unstable patients. If you use ultrasound in your ED, your department should have a quality improvement program set up that is approved by both ED administration and radiology.Use the right transducer
Soft tissue applications should be performed with a 5 to 7.5 MHz linear array transducer.Be generous with the gel
Apply a large amount of ultrasound gel to improve your acoustic interface. If the patient is thin and devoid of much subcutaneous fat, you may need to utilize an acoustic standoff pad to improve your sonographic window.Know normal
Start by scanning normal tissue margins surrounding the area of interest. Note that normal subcutaneous tissue will have dark, hypoechoic regions of fat mixed in with brightly hyperechoic muscle, facial, and tendon planes.Know abnormal
Abscesses may appear hypoechoic or anechoic during the initial stages of formation. As the inflammatory process progresses, the pus may begin to appear more heterogeneous with a mix of hypoechoic and hyperechoic material swirled together. Cysts should be hypoechoic. Masses will have different degrees of echogenicity depending on their composition.

Find another angle
Always obtain images in multiple planes (longitudinal, transverse, oblique) to help define the borders.

Don’t cut vital structures
If planning a procedure, first identify surrounding nerves, lymphatic channels, and vessels to help prevent accidental injury to these structures. Remember that pseudoaneurysms and large vessels may look like a cyst or an abscess on ultrasound. If you image in multiple planes, a vessel will appear as a cylinder but cysts and abscesses remain egg-shaped. When in doubt, apply color-Doppler to the area of concern.

Use the comparison view
Utilize contra-lateral limbs and adjacent areas of normal appearing tissue for comparison
Practice Makes Perfect: With bedside ultrasound there is no substitute for experience. The more ultrasounds you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is. An image library of normal and abnormal ultrasounds helps immensely and EPMonthly.com can take you there. Just go to EPMonthly.com, select “Departments”, chose “Real-Time-Readings” and click on the “Ultrasound Library” link.

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