Test yourself
Necrotising fasciitis: look below the cobblestones
5 questions. Pick an answer to see whether you are right and why. Your score appears at the end.
Question 1What does STAFF stand for in the ultrasound assessment for necrotising fasciitis?
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Answer c. STAFF describes the three ultrasound findings: thickened subcutaneous tissue, air (gas) in the soft tissue, and fluid along the deep fascia. Thickening alone is common in cellulitis. Air and fascial fluid raise concern.
Question 2Which finding most separates necrotising fasciitis from simple cellulitis?
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Answer d. Cellulitis causes thick, bright fat and cobblestoning, with a clean deep fascia. Fluid tracking along the deep fascia suggests infection spreading in the fascial plane. A fluid layer of more than 4 mm was the threshold used in an emergency department study.
Question 3Bright spots with dirty shadowing appear in the soft tissue of a painful, red thigh. There is no wound or recent injection. What do they suggest?
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Answer d. Gas gives bright echoes with grey, dirty shadowing or ring-down behind them. Without a wound, injection or recent surgery to explain it, gas in the soft tissue of an infected limb needs an immediate surgical review.
Question 4A patient has severe pain in the calf out of proportion to mild redness, a raised heart rate and a normal ultrasound. What do you do?
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Answer d. Ultrasound misses some cases, especially early in the disease. Clinical suspicion drives the decision. Surgical exploration is both the diagnosis and the treatment, and delay increases mortality.
Question 5Why do you scan normal skin before the red area?
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Answer a. Fat thickness and brightness vary between patients and body areas. A comparison view tells you whether the fat over the red area is thicker than normal and whether the fascia has changed.
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