Your ODA is on a training mission in the southern Philippine islands. While conducting base defense improvements and inspections, your engineering sergeant (18C) has an accident resulting in a large splinter impaled into his right upper thigh. You remove it and 2 days later the 18C complains of pain, swelling, warmth, and redness around the initial puncture wound.

On physical examination (PE), the patient is well- appearing and afebrile. All his vital signs are within normal limits. The upper portion of the right anterior thigh and his right groin are red, tender to touch, warm, and the skin is indurated. You palpate a tender lump in the right groin. Your junior medic is already preparing for the incision and drainage (I&D) procedure. However, your sixth sense is telling you to grab an ultrasound probe first! To cut or not to cut – that is an ultra sound question, isn’t it?

1. What typical sonographic findings of cellulitis do we observe in Figure 1 (image on the left)?
2. What treatment and procedures are indicated?

CLiNiCAL CONSiDERATiONS

Such physical exam findings in a young and otherwise healthy, well-appearing and afebrile male generally do not require any extensive clinical considerations or a broad differential diagnosis. It is quite clear this patient most likely has cellulitis, yet the presence of a tender lump, makes you wonder if he also has an associated abscess. In someone who looks so well, probability of a deep space infection, such as necrotizing fasciitis, is rather low (and we will leave it for another story).

Now, in settings of extensive cellulitis, trying to differentiate between cellulitis vs abscess with surrounding cellulitis based solely on PE findings, is quite a challenge. In fact, you might flip a coin just as well [1].

Treatment of cellulitis in a patient without symptoms of systemic toxicity (fever, chills, etc…), even if associated with abscess formation, is not a rocket science. If the patient has an abscess, you drain it! If all they have is cellulitis, you treat it with antibiotics. So simple is that.

Also, don’t forget that any patient with (extensive) cellulitis, requires close reassessment after initiation of antibiotic treatment. Mark the borders of erythema and/or have them take a smart-phone picture, and reassess at 24 hrs. 

OPERATiONAL CONSiDERATiONS

Uncomplicated cellulitis +/- an abscess obviously does not require your patient to be evacuated. But if you leave it untreated, you certainly risk opening yet another can of worms. 

In tactical environments, thinking that someone might need a procedure + performing an unnecessary intervention, vs knowing they certainly require a given invasive treatment is most definitely crucial. 

SONOGRAPHiC MiSSiON SUPPORT

Looking at the images obtained while scanning the patient’s right groin, there are two findings that immediately draw your attention. 

1. Cobblestoning – fat lobules in the subcutaneous (adipose) tissue which are floating in the anechoic (black) fluid. This creates such a classic “cobblestoning appearance of cellulitis. Yep! Even SOF operators have a little bit of subQ fat ;-). 
2. Presence of a “collection” – this hypoechoic structure with posterior acoustic enhancement artifact could be easily mistaken for a walled-off abscess, while it is one of the abscess mimics. 

In early cellulitis we don’t see cobblestoning just yet. During ultrasound examination the involved area appears thickened in comparison to the unaffected site. Also, all the skin layers seem to be blending together. The affected tissue is almost equally echogenic all the way down to the superficial fascia, and that’s why it is more difficult to discern all the different layers of such intensely inflamed skin [2]. 

Cobblestoning, which is consistent with pretty advanced edema, sets in later. Of course, in the appropriate clinical scenario, it is indeed diagnostic of cellulitis. FYI though – not every patient with cobblestoning has cellulitis. Just as an example, a patient with leg swelling from heart failure would also show cobblestoning, if you scan their legs.  

Getting back to our most important question: 2 cut or not 2 cut? While the hypoechoic round structure could easily pass for a walled-off abscess, you must actually make sure that it is not an abscess mimic. If you see internal blood flow inside the surveyed structure on color Doppler, it is not an abscess. It could be a blood vessel surrounded by cellulitis or an inflamed reactive lymph node, like in our case. Lymph nodes scanned in color Doppler mode, show such a classic branching vascular stalk. In case of an abscess, you would only see increased vascular flow around the cavity, but none inside (we will cover it with another case).

Ultrasound diagnostics for abscess vs cellulitis is very easy! As research has shown, “non physician military medical providers (Medics, PA’s…) can be trained in a very brief period to use #SOFsono to detect superficial soft tissue abscesses with excellent accuracy” [3].

1. Tayal VS et al. The effect of soft-tissue ultrasound on the management of cellulitis in the emergency department. Acad Emerg Med. 2006; 13: 384-8.
2. Gharahbaghian L et al. Point-of-care ultrasound in austere environments. Emerg Med Clin North Am. 2017; 35: 409-441.
3. LaDuke M et al. Ultrasound detection of soft tissue abscesses performed by non-shysician U.S. Army medical providers naïve to diagnostic sonography. Mil Med. 2017; 182: e1825-e1830.