By Frances Russell, MD and Taylor Duncan, MD
Chief Complaint: Thigh Pain
1. What are the findings in the Video?
2. How do these findings differ from simple cellulitis and abscess?
3. How reliable is point-of-care ultrasound for diagnosing this condition?
A 29 year old female with poorly controlled type II diabetes presented with one week of progressively worsening redness, pain and swelling in her left inguinal region and proximal thigh. She also complained of subjective fevers, nausea, and vomiting.
Physical exam disclosed a mildly distressed female. Vital signs were HR 106, BP 105/84, RR 12, T 98.6 and SpO2 100%. A 5-cm area of swelling, erythema, warmth and tenderness to palpation was found on the left proximal medial thigh. There was no tenderness beyond the margin of erythema. The remainder of her exam was unremarkable.
An ultrasound was performed at the bedside to evaluate for possible abscess. Based on the ultrasound findings, general surgery was immediately consulted and broad spectrum antibiotics were initiated.
A computed tomography (CT) scan (Image 2) was performed at the request of surgery, and the patient was taken that morning to the operating room for debridement. Surgery debrided a total of 46 cm of tissue, and the patient was discharged from the hospital 7 days later in good condition.
Review of Necrotizing Fasciitis:
Necrotizing fasciitis is a rapidly progressing infection of the skin and soft tissue that results in significant morbidity and mortality.1 Prognosis is dependent on both early and accurate diagnosis.2 However this can be difficult as early stages of necrotizing fasciitis are identical in presentation to that of a simple abscess or cellulitis.1,3
Classic signs of necrotizing fasciitis include erythema, pain out of proportion to exam, swelling, and fever.3 Traditionally, CT and magnetic resonance imaging (MRI) have been used as adjuncts to clinical diagnosis.4,5 However, these modalities can be time consuming and may delay definitive treatment.
Ultrasound is an alternative imaging modality that may provide an accurate diagnosis and allow for earlier surgical intervention.4,6,7 Sensitivity and specificity of point-of-care ultrasound for detecting necrotizing fasciitis has been reported at 88% and 93%, respectively.7
Answers to questions:
1. The video clip is consistent with necrotizing fasciitis. Classic findings on ultrasound include fascial thickening, fascial irregularities, adjacent fascial fluid, and subcutaneous air.4,6,8 The video illustrates a large amount of subcutaneous gas, visualized as echogenic areas below the skin surface with posterior acoustic shadowing. You can also see a small amount of adjacent hypoechoic fluid.
2. Cellulitis (below left) appears sonographically as subcutaneous fluid and takes on a “cobblestone” appearance. Cobblestoning is due to hyperechoic fat that is surrounded by hypoechoic fluid. An abscess (below right) is a collection of anechoic or hypoechoic fluid that may have hyperechoic debris within it. An abscess may also have posterior acoustic shadowing.8
3. While there have been several case reports published on the use of point-of-care ultrasound to diagnose necrotizing faciitis,4,6,9 there is a paucity of prospective literature. One prior study by Yen et al, found point-of-care ultrasound has a sensitivity of 88% and a specificity of 93% for detecting necrotizing fasciitis in 62 patients. Here they used operative findings as the criterion standard.7
Point-of-care ultrasound may be used to rapidly rule-in necrotizing fasciitis in patients presenting with soft tissue pain and swelling. Detecting necrotizing fasciitis on ultrasound can expedite surgical intervention.