Imaging features of subcutaneous abscesses

This is an automatically translated article.

The article was written by MSc Tong Diu Huong - Radiologist, Department of Diagnostic Imaging - Vinmec Nha Trang International General Hospital
Subcutaneous abscesses are a manifestation of many soft-tissue skin infections, including cellulitis and necrotizing fasciitis.

1. What is a subcutaneous abscess?

Subcutaneous abscess is a type of abscess located in the dermis and dermis under the skin. Along with tooth abscess, subcutaneous abscess is one of the most common abscess sites.

2. Clinical manifestations of subcutaneous abscess

Patients typically present with an acute or subacute clinical presentation with localized swelling or mass in the affected skin with accompanying signs of cellulitis. If sepsis is present, the patient may have signs of systemic infection such as fever, malaise, and increased markers of inflammation.

3. Pathology

Bacterial skin abscesses spread into subcutaneous tissues through tears in the epidermis. Streptococcus has traditionally been the most common pathogen. Fungal abscesses are rare. In some cases, aseptic abscess formation has also been described when a drug or irritant is injected into the skin, resulting in aseptic inflammation and abscess formation.

4. Photographic characteristics

Subcutaneous abscesses are usually diagnosed clinically and do not require imaging modalities. In complicated cases where radical surgical treatment is being considered, imaging studies may be considered to determine the extent of spread in the soft tissue.
CT remains the imaging modality of choice for evaluation of abscesses.
Ultrasound is increasingly being shown to be useful in differentiating cellulitis from true abscesses. One study reported that ultrasound evaluation changed management in half of cellulitis emergencies.
4.1. Ultrasound: Acoustic or hypoechoic circular fovea. An echogenic sheath may be present, but often the shoreline is not clear. A septum, sediment, or even air may be seen within the center of the cyst. When compressing with the transducer, movement or swirling of the contents of the abscess can be produced. Cobblestone image of surrounding subcutaneous tissue due to edema of accompanying cellulitis. Doppler ultrasound showed increased perfusion in the soft tissue around the fluid collection, no Doppler signal inside the fluid.

Figure 2. Ultrasound image of the groin area of ​​a 25-year-old male patient: The right inguinal soft tissue thickens, edema. Image of hypoechoic fovea with internal deposits, no Doppler signal inside the abscess.
4.2. CT Scanner Image of foci of hypoattenuation in subcutaneous soft tissue, irregular margins, border enhancement, and surrounding fat infiltrates.

Figure 3. Subcutaneous abscess in a 25-year-old male patient with groin pain and fever following groin injection. Contrast-enhanced CT image: the right groin has a collection of fluid with thick thickened walls (white arrows), consistent with the abscess. The subcutaneous soft tissue surrounding the fovea was swollen and absorbent, consistent with cellulitis. Note the relatively intact subcutaneous fat in the lateral and posterior thighs for comparison. A broken piece of needle (black arrow) is seen deep in the fovea.

5. Differential diagnosis

Possible imaging differentials include:
Enlarged lymph nodes Sebaceous cysts Intestinal hernias Blood vessels

6. Treatment

Incision and drainage of abscess
Antibiotic therapy if signs of systemic infection, widespread cellulitis, or for those with risk factors (eg, immunosuppressed patients, or diabetes).
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