Ultrasound Features of Mastitis
Mastitis on ultrasound typically demonstrates parenchymal edema, skin thickening, fluid collections/abscesses, and hypoechoic masses, with the combination of collections and parenchymal edema being particularly characteristic of the condition.
Key Ultrasound Findings
Primary Features
The most common and diagnostically useful ultrasound findings in mastitis include 1, 2:
- Parenchymal edema (48.2% of cases) - appears as diffuse increased echogenicity and tissue thickening
- Fluid collections/abscesses (66.7% of cases) - ranging from simple to complex fluid collections
- Skin thickening (21.5% of cases) - diffuse or focal thickening of the breast skin
- Hypoechoic masses (31.4% of cases) - irregular or ill-defined hypoechoic areas within the parenchyma
Highly Specific Combination
The simultaneous presence of both collections AND parenchymal edema (seen in 32.3% of cases) is particularly useful for differentiating mastitis from other breast lesions 2. This combination may reduce the need for immediate biopsy when clinical symptoms are consistent with mastitis.
Distinguishing Infectious vs Non-Infectious Mastitis
Infectious Mastitis Features 1
- Diffuse edema with inflammatory changes
- Diffuse skin thickening
- Multiple collections or frank abscesses
- More commonly shows fluid-filled structures
Non-Infectious Mastitis Features 1
- Typically presents as solitary or multiple discrete breast masses
- More solid-appearing lesions
- Less diffuse edema
- May show complex cystic components 3
Additional Ultrasound Characteristics
Associated Findings 2
- Axillary lymphadenopathy (50.2% of cases)
- Cortical thickening present in 61.9% of enlarged nodes
- Fistulae (5% of cases) - tract-like hypoechoic structures extending to skin
- Vascular changes - increased vascularity on color Doppler
BI-RADS Classification 2
Most mastitis cases are categorized as:
- BI-RADS 4 (46.4%) - suspicious abnormality
- BI-RADS 3 (30.4%) - probably benign
Critical Pitfall: Distinguishing from Malignancy
Mastitis can mimic inflammatory breast cancer both clinically and radiologically 4, 1. Key considerations:
- Failure to respond to antibiotics after 7-10 days should raise suspicion for malignancy 5
- Persistent clinical signs despite treatment warrant biopsy
- Some breast cancers can present with falsely benign-appearing features including circumscribed margins and posterior acoustic enhancement 6
- When imaging and clinical findings suggest mastitis but are atypical or persistent, core needle biopsy is mandatory to exclude malignancy
Role of Adjunctive Imaging
Strain Elastography 7
- Improves classification accuracy to 65.8% when combined with conventional ultrasound
- Helps differentiate mastitis subtypes
- Mean elastography scores differ significantly between subtypes
Contrast-Enhanced Ultrasound 7
- Shows hyperenhancement with or without increased lesion size
- Less useful for subtype classification
- Cannot reliably distinguish between mastitis types
Mammography
- Limited role in acute mastitis due to pain and increased breast density 4, 8
- May show focal asymmetry as the most common finding 1
- More useful after acute phase resolution
Clinical Algorithm
- First-line imaging: Ultrasound is the modality of choice 4, 8
- Look for the diagnostic combination: Collections + parenchymal edema
- Assess for complications: Abscesses requiring drainage
- Evaluate lymph nodes: Check for axillary involvement
- If atypical or persistent: Proceed to core needle biopsy regardless of imaging appearance
- If no response to antibiotics in 7-10 days: Mandatory biopsy to exclude inflammatory breast cancer 5