From the Guidelines
Ultrasound is the preferred first-line imaging modality for differentiating cellulitis from abscess in the head and neck due to its accessibility, lack of radiation, and real-time capability. This recommendation is based on the most recent evidence, which highlights the importance of choosing the right imaging modality to guide diagnosis and treatment 1.
Key Considerations
When differentiating cellulitis from abscess, it's crucial to consider the patient's clinical status, the suspected depth of infection, and the availability of equipment. Ultrasound excels in detecting subperiosteal and soft-tissue abscesses, tenosynovitis, joint effusions, and radiolucent foreign bodies 1.
Imaging Modalities
- Ultrasound: Offers real-time capability, lack of radiation, and is particularly useful for guiding diagnostic aspiration or therapeutic drainage in emergency settings.
- CT with contrast: Provides excellent soft tissue detail and is valuable for evaluating deeper structures when ultrasound is limited. It can assess soft tissue and the extent of infection, guiding aspiration or surgical debridement 1.
- MRI: Offers superior soft tissue contrast and is valuable for complex cases or when neurological involvement is suspected, though it may be challenging for unstable patients.
Characteristics of Cellulitis and Abscess on Imaging
- Abscesses on ultrasound: Typically appear as hypoechoic or anechoic fluid collections with posterior acoustic enhancement.
- Cellulitis on ultrasound: Shows diffuse hyperechoic changes in subcutaneous tissues with increased vascularity on Doppler.
- Abscesses on CT: Present as hypodense collections with rim enhancement after contrast administration.
- Cellulitis on CT: Appears as diffuse soft tissue stranding and fat plane obliteration.
The choice between these modalities should be guided by the clinical context, emphasizing the need for a tailored approach to each patient's specific situation, prioritizing morbidity, mortality, and quality of life outcomes 1, 1.
From the Research
Imaging Modalities for Differentiating Cellulitis vs Abscess
- The use of imaging modalities such as ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) can aid in differentiating cellulitis from abscess in the head and neck region 2, 3.
- Bedside ultrasound can be a valuable tool in ruling out suspected abscess by allowing direct visualization of a fluid collection, and can also determine the proximity of the infection to adjacent structures 2.
- CT and MRI can provide detailed images of deep neck space infections, including phlegmon and abscess, and can help guide incision and drainage under imaging guidance 3.
- Point-of-care ultrasound (POCUS) can be used by associate providers to accurately detect soft tissue abscesses, with high sensitivity and specificity, and can change management decisions in a clinically relevant number of patients 4.
Comparison of Imaging Modalities
- Ultrasound is a useful tool for differentiating cellulitis from abscess, especially in cases where physical exam is unclear 2, 4.
- CT and MRI can provide more detailed images of deep neck space infections, but may not be necessary for all cases of cellulitis or abscess 3.
- POCUS has been shown to be accurate and reliable when used by associate providers, and can increase the ability to rule in the diagnosis of abscess 4.
Clinical Significance
- Accurate diagnosis and differentiation of cellulitis from abscess is crucial for timely and effective treatment, as abscesses often require incision and drainage in addition to antibiotics 5, 6.
- Imaging modalities can aid in this diagnosis, and can help guide treatment decisions, including the need for incision and drainage or antibiotic therapy 2, 3, 4.