This post is in response to the August Ultrasound Image of the Month: “To Drain Or Not To Drain? That Is The Question.”
To summarize, we had a febrile 1-year-old male presenting to the ED with a 2cm area of redness and induration behind that right knee that was concerning for a soft tissue infection. A point-of-care ultrasound was performed and the following clip was obtained, suggesting an abscess.
Thank you to all of you who took the quiz! Here are your results below:
Only 18% guessed correctly that this patient had an abscess. Most respondents were split between cellulitis (36%) and a baker’s cyst (27%). A small percentage guessed that this patient had a foreign body and only 5% said that the ultrasound was normal.
Soft Tissue Infections
Subcutaneous soft tissue infections (SSTI’s) are a common presentation in the Pediatric Emergency Department. Some arrive as mere pimples or furuncles, others with copious purulent goo coming out on simple palpation. But many others will present with redness and induration, leaving the examiner to wonder, could there be a fluid collection under there?
Normal
In normal subcutaneous tissue, the epidermis and dermis appear as a thin, hyperechoic layer. The subcutaneous layer is comprised of hypoechoic fat with hyperechoic linear connective tissue.
Cellulitis
Sonographically, cellulitis is seen as hyperechoic fat lobules that are separated by hypoechoic fluid-filled areas, classically described as having a cobblestone appearance.
Abscesses
Abscesses are generally thought of as localized fluid collections that should appear round and hypo- or anechoic.
In the era of MRSA…
In the era of MRSA, abscesses can have an irregular area of hypo- to iso- to hyperechoic fluid collection. With some of the iso- or hyperechoic collections, additional information such as posterior acoustic enhancement or fluid movement within the cavity will help to distinguish an abscess from surrounding cellulitic tissue.
In our patient, the initial ultrasound still images did not demonstrate an obvious hypo- or anechoic fluid collection. However, when the probe was pushed down onto the area of induration, there is notable fluid movement in the left upper side of the image consistent with an abscess. Incision and drainage produced a large amount of purulent drainage, confirming the presence of an abscess.
In the literature, two adult ED studies have shown that sonography changes management in SSTI’s, with two pediatric studies showing changes in management and another not showing as much benefit.
How to perform soft tissue ultrasounds.
Other sonographic soft tissue findings.
Test your knowledge of soft tissue ultrasound.
If you want to see YOUR image included in the next Image of the Month, please email interesting stills and/or clips in addition to a small blurb on the patient to Lorraine Ng at PEMFellowscom@gmail.com.
Lorraine Ng
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