Now that Greg has made you afraid of necrotizing fasciitis…as you should be!
Greg posted a couple of cool cases of necrotizing fasciitis in December. We had a case of nec fasc in our department in the last few months that has made everyone quite wary! It has dropped our threshold for worrying about this nasty entity. I saw a patient last month who presented with diffuse cellulitis of their left lower leg. There was no palpable crepitus. But crepitus may not be felt in a case that presents early. So I put the probe on looking for signs of gas. And this is what I saw.
To be honest, I wasn’t especially concerned about nec fasc, so the images on the screen threw me. As I slid through the affected area, I could see discrete areas of shadowing come and go which made me concerned that this might represent gas. So I decided to get an x-ray.
This patient had multiple areas of soft-tissue calcification throughout her lower leg on x-ray. This can develop in patients with venous stasis, as was the case in this patient. When you review the video, you can see that the shadowing is quite sharp, unlike the shadowing often seen with gas. Also, where the shadowing originates in the near field, there are tiny areas of echogenicity. These are consistent with the calcifications seen on the x-ray. Keep these in mind as a potential false-positive for gas.
I had a similar case. A patient didn’t really seem to have Necrotizing Fasciitis but POCUS looked very much like the above. It scared me and I put the patient on Abx. and referred her. It turned out to be nothing serious. In retrospect I think I was looking at an area of fat necrosis.
Yep, I’ve seen this false-positive too. As in your case, the sharp (as opposed to dirty) shadowing and corresponding calcifications on the x-ray clarified things for me.
Glad I’m not alone!