Pediatric Subcutaneous Abscess

Etiology: Bacteria (typically streptococcus) spread into subcutaneous tissues through breaches in epidermis forming an abscess which lies within the dermis and subdermal cutaneous layers
Imaging: Evaluate extension of collection looking for natural borders like fat and muscle interface or nearby cortical bone surface
Imaging US:
— Round collection of anechoic or hypoechoic fluid which may show internal motion or swirling with compression
— Borders often poorly defined
Imaging MRI:
— T1WI post contrast: Enhancing rim with shaggy border
DDX: Lymph node, hematoma, inflammatory collection
Complications:
Treatment: Surgical
Clinical:
— Typically presents as focal swelling with cellulitis in surrounding skin
— May present with systemic signs of sepsis if bacteremia is present
— Gluteus muscle is common site

Radiology Cases of Subcutaneous Abscess

US of subcutaneous abscess of knee — Transverse color doppler US of the left calf just inferior to the patella shows a well circumscribed, hypoechoic lesion in the sucutaneous tissues that is hypervascular in nature.

US of subcutaneous abscess — Transverse US of the axilla centered on the palpable mass shows an oval hypoechoic lesion in the subcutaneous tissue.

CT of pediatric subcutaneous abscess — Axial (above left) and sagittal (above right) CT with contrast of the face in soft tissue windows show a large low density rim enhancing fluid collection in the center of the subcutaneous tissue of the forehead. Axial (below left) and sagittal (below right) CT in bone windows show the paranasal sinuses are clear and there is no bone destruction.