Can Fluid Accumulation on Ultrasound Diagnose Necrotizing Fasciitis?

necrotizing fasciitis


Necrotizing fasciitis (NF) is rapidly progressing, severe soft tissue infection with a mortality rate of 19.3% with treatment and significantly higher without treatment (1). Early diagnosis is essential to prompt surgical intervention and reduce morbidity and mortality. However, treatment can often be delayed because no laboratory or imaging test can definitively diagnose NF. Contrast-enhanced CT shows the best accuracy, but again is not perfect and can be difficult to obtain in unstable patients. MRI is similarly accurate, but even less feasible in the Emergency Department. Ultimately, it remains a surgical diagnosis.

Ultrasonography is a rapid, bedside, and non-invasive tool that has potential to accelerate assessment of patient with clinical suspicion for NF. There are ultrasonographic findings associated with NF diagnosis, including irregularity or thickening of deep fascia, subcutaneous emphysema, and fluid accumulation along the deep fascial plane (2-13). Considering this condition’s rapid progression, ultrasonography may enable physicians to quickly gauge disease severity and triage accordingly, prompting earlier surgery and bettering patient outcomes.

The Relationship Between Fluid Accumulation in Ultrasonography and Diagnosis and Prognosis of Patients with Necrotizing Fasciitis


Clinical Question

What is the relationship between ultrasonographic finding of fluid accumulation along the deep fascia and diagnosis and prognosis of necrotizing fasciitis?

What ultrasonographic findings are significantly different between NF patients and non-NF patients?

What is the ultrasonographic-detected depth of fluid accumulation along the deep fascia that offers the greatest accuracy to diagnosis of NF?

Is there a difference in the prognosis between NF patients with fluid accumulation compared to NF patients without fluid accumulation? 

Methods & Study Design

• Design 

Retrospective study with prospective enrollment

• Population 

This study was conducted at Chang Gung Memorial Hospital, a suburban academic tertiary care hospital.

Inclusion criteria: patients who visited the ED from February 2015 – November 2016 with clinical suspicion of NF of limbs based on symptoms and clinical signs (severe pain out of proportion, skin findings, rapid progression, crepitus, skin bullae, necrosis, or ecchymosis).

NF group: discharge diagnosis of NF, confirmed by pathology report showing necrosis after surgical intervention

Non-NF group: did not have surgical intervention or whose pathology report did not support NF diagnosis

Exclusion criteria: patients with ED visits between 24:00 – 7:00, non-lesion side also has fluid accumulation, age <18yo, prior antibiotics or debridement, lesions involving trunk area

• Intervention 

Ultrasonographic exam within 1 hour after ED arrival completed by one of three experienced emergency physicians who received an 8-hour basic and soft-tissue ultrasonographic training before the study

Orthopedic consult for surgical opinion

• Outcomes  

  • Diagnostic markers: irregularity or thickening of deep fascia, fluid accumulation, subcutaneous emphysema, subcutaneous cobblestone
  • Reasonable cutoff value of fluid accumulation along deep fascial plane for diagnosing NF according to receiving operating characteristic (ROC) curve
  • Prognostic markers: length of stay (LOS) in hospital, mortality, amputations, number of operations


Ultrasound finding of fluid accumulation and irregular or thickened fascial layer were significantly different between NF and non-NF groups. All patients who had subcutaneous emphysema were in the NF group.

The best cutoff point of fluid accumulation to diagnose NF was 2mm, which had the best accuracy (72.7%), with sensitivity of 75%, a specificity of 70.2%, a positive predictive value of 71.7% and a negative predictive value of 72.7%.

NF patients with fluid accumulation had longer length of stay than NF patients without fluid accumulation (average: 39 days vs. 23 days). Number of operations were not significantly different between NF patients with and without fluid accumulation. All NF patients who had an amputation or died had fluid accumulation.


Overall mortality between NF and non-NF groups showed no significant difference.

Strength & Limitations


  • Sample size was larger than other studies investigating ultrasonographic findings for NF diagnosis.
  • Study had a comparator groups with clear definitions (NF vs. non-NF).
  • Ultrasound training was standardized and assessed with inter-rater reliability between three emergency physicians as 100%.


  • Small, imbalanced sample of NF patients for sensitivity and specificity analysis of fluid accumulation for amputation and mortality. 
  • Study excluded patients with truncal soft tissue infections.
  • Study excluded patients with prior antibiotics or debridement, which may have been NF patients with higher severity and worse prognosis.
  • Patient population were from south Taiwan exclusively.
  • NF patients had higher prevalence of specific co-morbidities (diabetes mellitus, liver cirrhosis, and alcohol use disorder), which could be confounding. 

Authors Conclusion

“The ultrasonographic finding of fluid accumulation along the deep fascia with a cutoff point of more than 2 mm of depth may aid in diagnosing NF. For the prognosis of NF, when fluid accumulation was present along deep fascia on ultrasound, patients with NF had longer lengths of hospital stays and were at risk of amputation or mortality. Ultrasonography is a point-of-care imaging tool that facilitates the diagnosis and prognosis of NF.” (14)

Our Conclusion

Consistent with prior studies and case reports (2-13), this study supports the role of ultrasound in the diagnosis of NF. Trained emergency physicians were able to successfully use ultrasound to detect significant imaging differences in NF patients, including fascial irregularity and deep fascial fluid accumulation. In comparison to Yen et al., this study suggests an even lower cutoff point of fluid accumulation along the deep fascia (2mm vs 4mm) for the highest diagnostic accuracy. We would caution that the finding of "fluid accumulation" was somewhat difficult to interpret in their study.

Further studies with larger sample sizes need to be completed. However, with the diagnostic and prognostic trends seen in this study, ultrasound should be considered as a timely, efficient imaging modality that can help identify patients with clinical suspicion of NF and accelerate OR intervention.

The Bottom Line 

Ultrasound is a viable imaging modality for patients with clinical suspicion of NF that could potentially expedite surgical intervention, though imaging findings may not be as easy to interpret as the authors lay out.


This post was written by Caresse Vuong, Charles Murchison MD and Amir Aminlari MD.


  1. Khamnuan P, Chongruksut W, Jearwattanakanok K, Patumanond J, Yodluangfun S, Tantraworasin A. Necrotizing fasciitis: Risk factors of mortality. Risk Manag Healthc Policy 2015;8:1–7.
  2. Castleberg E, Jenson N, Am Dinh V. Diagnosis of necrotizing fasciitis with bedside ultrasound: The STAFF exam. West J Emerg Med 2014;15:111–113.
  3. Tsai CC, Lai CS, Yu ML, Chou CK, Lin SD. Early diagnosis of necrotizing fasciitis by utilization of ultrasonography. Kaohsiung J Med Sci 1996;12:235–240.
  4. Wronski M, Slodkowski M, Cebulski W, Karkocha D, Krasnodebski IW. Necrotizing fasciitis: Early sonographic diagnosis. J Clin Ultrasound 2011;39:236–239.
  5. Yen ZS, Wang HP, Ma HM, Chen SC, Chen WJ. Ultrasonographic screening of clinically-suspected necrotizing fasciitis. Acad Emerg Med 2002;9:1448–1451.
  6. Bernardi, Emanuele, Antonello Iacobucci, Letizia Barutta, Elisa Pizzolato, Virna Olocco, and Bruno Tartaglino. “A-Lines in Necrotizing Fasciitis of the Lower Limb.” Journal of Ultrasound in Medicine 33, no. 11 (2014): 2044–46. 
  7. Chao, H. C., M. S. Kong, and T. Y. Lin. “Diagnosis of Necrotizing Fasciitis in Children.” Journal of Ultrasound in Medicine: Official Journal of the American Institute of Ultrasound in Medicine 18, no. 4 (April 1999): 277–81. 
  8. Hosek, William T., and Timothy C. Laeger. “Early Diagnosis of Necrotizing Fasciitis with Soft Tissue Ultrasound.” Academic Emergency Medicine 16, no. 10 (2009): 1033–1033. 
  9. Oelze, Lindsay, Stanley Wu, and Jennifer Carnell. “Emergency Ultrasonography for the Early Diagnosis of Necrotizing Fasciitis: A Case Series from the ED.” The American Journal of Emergency Medicine 31, no. 3 (March 1, 2013): 632.e5-632.e7. 
  10. Kehrl, Thompson. “Point-of-Care Ultrasound Diagnosis of Necrotizing Fasciitis Missed by Computed Tomography and Magnetic Resonance Imaging.” The Journal of Emergency Medicine 47, no. 2 (August 2014): 172–75. 
  11. Shyy, William, Roneesha S. Knight, Ruth Goldstein, Eric D. Isaacs, and Nathan A. Teismann. “Sonographic Findings in Necrotizing Fasciitis.” Journal of Ultrasound in Medicine 35, no. 10 (2016): 2273–77. 
  12. Hanif, Muhammad A., and Michael J. Bradley. “Sonographic Findings of Necrotizing Fasciitis in the Breast.” Journal of Clinical Ultrasound: JCU 36, no. 8 (October 2008): 517–19. 
  13. Valle Alonso, Joaquín, Ganapathiram Lakshmanan, and Yasser Saleem. “Use of POCUS Ultrasound in Sepsis, Bedside Diagnosis of Necrotizing Fasciitis.” QJM: An International Journal of Medicine 110, no. 10 (October 1, 2017): 687–88. 
  14. Lin, Chun-Nan, Cheng-Ting Hsiao, Chia-Peng Chang, Tsung-Yu Huang, Kuang-Yu Hsiao, Yi-Chuan Chen, and Wen-Chih Fann. “The Relationship Between Fluid Accumulation in Ultrasonography and the Diagnosis and Prognosis of Patients with Necrotizing Fasciitis.” Ultrasound in Medicine & Biology 45, no. 7 (2019): 1545–50. 


Case # 7: A Case of Asymmetry

A 22 year old male presents to the emergency department with a sore throat for 1 week. The pain is predominately on the left side and is associated with difficulty opening his mouth and fever. He was placed on amoxicillin 3 days ago but notes that his symptoms have progressed. He appears uncomfortable.

Vitals: T 101.4 HR 105 BP 132/81  RR 14 O2 98% on RA

A bedside ultrasound is performed, what is the next best step in management?


Answer and Learning Point


Incision and drainage. The patient presents with lateralizing pharyngitis symptoms associated with fever and trismus concerning for peritonsillar abscess (PTA). The ultrasound clip demonstrates a well circumscribed, hypoechoic fluid collection abutting the left tonsil confirming this diagnosis (see color overlay below).

Previously, physicians relied solely on the physical exam findings of peritonsillar swelling and uvular deviation to make the diagnosis of PTA. However, this approach lacks accuracy, with studies showing a sensitivity and specificity of 75% and 50% respectively [1]. This uncertainty leads to increased CT utilization, repeat drainage attempts and ENT consultation. Intraoral ultrasound is a novel technique that can be used by emergency physicians (EP), both for diagnosis and drainage of PTA. A recent randomized control trial found the use of intraoral ultrasound (vs. traditional landmark technique) to be significantly more reliable for differentiating between PTA and peritonsillar cellulitis. Additionally, this study also demonstrated increased success in PTA drainage by EPs with the use of intraoral ultrasound guidance [2].

Data from Costantino et al

Learning Points

    • An endocavitary probe should be used when PTA is suspected to differentiated between PTA and peritonsillar cellulitis; and assist with drainage if necessary.
    • If an endocavitary probe is not available, or if the patient cannot open their mouth wide enough to pass the probe, an alternative approach, known as the telescopic submandibular approach can also be used and is explained here.
    • When using ultrasound, the distance from the oral mucosa to the center of the PTA should be measure. The plastic sheath of an 18-gauge needle (preferably a spinal needle to allow the barrel of the syringe to be outside of the patients mouth) should be cut to this length to prevent puncturing any deeper structures during drainage.


This post was written by Michael Macias, MD, Ultrasound Fellow at UCSD.


    1. Scott PM, e. (2017). Diagnosis of peritonsillar infections: a prospective study of ultrasound, computerized tomography and clinical diagnosis. - PubMed - NCBI . Retrieved 2 October 2017, from
    2. Costantino TG, e. (2017). Randomized trial comparing intraoral ultrasound to landmark-based needle aspiration in patients with suspected peritonsillar abscess. - PubMed - NCBI . Retrieved 2 October 2017, from

Case # 3: Under Your Skin

A 52 year old male with presents with 4 days of painful swelling and redness to his middle right thigh. Physical exam shows a 3 cm area of erythema that is tender to touch. He denies fever and trauma to the area. A bedside ultrasound is performed as seen below. What is the next step in management?

Vitals: HR 82 BP 110/72 RR 14 O2 98 (28)

Answer and Learning Point


Incision and drainage. The image above demonstrates a well circumscribed fluid collection within the soft tissue,  without evidence of surrounding cellulitis. The above abscess was incised with immediate release of a large volume of purulent material. The patient did well.

Learning Point

    • Ultrasound is an excellent adjunct to the physical exam in the evaluation of soft tissue infections. It improves accuracy in the diagnosis of superficial abscesses and has been shown to change management in up to 50% of emergency department cases of clinical cellulitis [1,2].
    • The ultrasound image above is atypical for an abscess given the iso-echoic texture appreciated in the fluid and is easily missed if the operator is not aware of this unusual finding. Most abscesses will appear as a hypoechoic fluid collection, however occasionally they may have increased internal echoes which can lead to false negative ultrasound results.
    • This can be avoided by applying gentle pressure to the area of the suspected cellulitis/abscess to evaluate for the "swirl sign" which is indicative of fluid movement within the abscess cavity [Figures 1&2].
    • This can be distinguished from the common pattern appreciated in cellulitis known as "cobblestoning" which indicates increased subcutaneous fluid.
Figure 1: Soft tissue ultrasound demonstrating swirling of iso-echoic fluid collection consistent with abscess. Image courtesy of UOTW.
Figure 2: Additional soft tissue ultrasound demonstrating the "swirl sign." Image courtesy of UOTW.


 Tayal VS, e. (2017). The effect of soft-tissue ultrasound on the management of cellulitis in the emergency department.

Squire BT, e. (2017). ABSCESS: applied bedside sonography for convenient evaluation of superficial soft tissue infections.

UOTW: Case 66