ZSFG AM Report Pearls 1/17/2018: Almost Doesn’t Count or Does It? Sensitivity of CT for Necrotizing Fasciitis

The topic of necrotizing fasciitis has been extensively explored on the Chief’s Blog, and today we are looking into whether CT is a good test for ruling out (i.e. has a high sensitivity) for necrotizing fasciitis. In the evernote below, I have integrated some of the prior nec fasc postings and included this update.

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Sensitivity of CT for Necrotizing Soft Tissue Infections:

In a single-site study at MGH, published in Archives of Surgery

Methods:

  • Patient with suspicion of necrotizing skin/soft tissue infection (NSTI) but who did not have obvious NSTI (those people were taken straight to OR).
  • CT scan findings (specifically 1.) asymmetric and diffuse areas of soft tissue inflammation and ischemia, 2.) muscle necrosis, 3.)gas across tissue planes, and 4.) fluid collections) compared to surgical findings.

Results:

  • 85 patients with suspected NSTI (18 directly taken to OR),
    • leaving 67 patients to undergo CT prior to surgical exploration
    • 58 (87%) underwent surgical exploration
      • 25 (37% of all patients and 43% of those who underwent surgical exploration) had confirmed NSTI
      • 33 had non-NSTIs and did not require debridement or had an isolated abscess + 9 more who were medically managed
    • All patients has their NSTI correctly diagnosed by CT scanning (met one of the four criteria for NSTI), there were no false-negative test results.
      • There were 8 (19%) false-positives
    • Ultimately, the sensitivity was 100%, Specificity 81%, PPV 76%, NPV 100%

CT nec fasc

Limitations:

  • In 1 patient, the first scan was equivocal and had to be repeated 12 hours later, this would be debatable as an actual false-negative
  • The CT findings most commonly found were asymmetric and diffuse areas of soft tissue inflammation and fluid collection, this can be conflated with a polymyositis
  • This was a single-site study with a relatively small number of patients

 

Sources:

  • Zacharias N et al. 2010. Diagnosis of necrotizing soft tissue infections by computed tomography. Arch Surg. 145(5):452-455

Evernote:

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