From the Guidelines
Yes, ultrasound can be performed to evaluate a possible soft tissue abscess, with a sensitivity of 96.7% and specificity of 85.7% for diagnosing abscesses, as reported by Gaspari et al 1. Ultrasound is an excellent first-line imaging modality for this purpose as it can clearly distinguish between cellulitis (diffuse inflammation) and an abscess (fluid collection) that may require drainage. The procedure is quick, painless, non-invasive, and doesn't expose the patient to radiation. During the examination, a healthcare provider will apply gel to the area of concern and move a handheld transducer over the skin. An abscess typically appears as a hypoechoic (dark) fluid collection with possible internal debris and increased blood flow around its periphery. The real-time nature of ultrasound also allows for immediate guidance if drainage is needed, helping the clinician locate the optimal entry point and avoid nearby blood vessels or other structures. Some key points to consider when using ultrasound for soft tissue abscess evaluation include:
- Ultrasound is particularly useful for abscesses in superficial locations such as the skin, breast, neck, and extremities, though deeper abscesses may require additional imaging like CT or MRI for complete evaluation, as noted in the study by Gaspari et al 1.
- The use of color Doppler can assess vascularity and hyperemia without the administration of IV contrast, as mentioned in the study 1.
- Ultrasound-guided aspirations of soft tissue fluid collections and joint effusions are becoming increasingly common, with a study by the American College of Radiology 1 highlighting its effectiveness.
- The overall sensitivity and specificity of US for the diagnosis of an abscess were reported as 96.7% and 85.7%, respectively, in the study by Gaspari et al 1, making it a reliable diagnostic tool.
From the Research
Ultrasound for Soft Tissue Abscess Diagnosis
- Ultrasound is a valuable tool in the evaluation of skin and soft tissue infections, including abscesses 2.
- It can help diagnose an abscess cavity or deeper infection, and is more reliable than clinical exam alone 2, 3.
- Point-of-care ultrasound (POCUS) can improve management of soft tissue skin infections by detecting occult abscesses, preventing unnecessary procedures, and identifying more complex disease requiring further imaging 3.
Comparison with Other Imaging Modalities
- Ultrasound has been compared to computerized tomography (CT) for diagnosing soft tissue abscesses, with ultrasound demonstrating higher sensitivity (96.7% vs 76.7%) but lower specificity (85.7% vs 91.4%) 4.
- Power Doppler sonography can also be used to depict increased vasculature and hyperemia around superficial soft tissue abscesses, similar to CT findings 5.
Operating Characteristics of Ultrasound
- The operating characteristics of POCUS for diagnosing abscesses in skin and soft tissue infections have been reported, with a sensitivity of 97%, specificity of 83%, positive likelihood ratio of 5.5, and negative likelihood ratio of 0.04 6.
- POCUS can assist physicians in distinguishing abscess from cellulitis, particularly in cases where physical examination is equivocal 6.