Other Finding — Enhancing Skin Lesions
Enhancing skin lesions are enhancing lesions of the skin unrelated to a current or suspected breast cancer. They are common incidental findings on breast MRI and in general need not be reported (BI-RADS v2025, p. 151).
Definition
A benign enhancing lesion originating within the dermis or epidermis that demonstrates contrast uptake on post-contrast T1-weighted imaging. The key distinction is that these lesions are skin-based, not arising from the breast parenchyma, and are unrelated to any underlying malignancy.
Common Examples
| Lesion | Typical Appearance |
|---|---|
| Moles (nevi) | Small, well-circumscribed, superficial enhancing nodule projecting from skin surface |
| Keloids | Elongated or nodular enhancing soft tissue along a surgical scar |
| Epidermal inclusion cysts | Round, well-circumscribed dermal lesion; may show peripheral enhancement |
| Sebaceous cysts | Round dermal lesion with variable enhancement; may contain T1-bright proteinaceous material |
| Skin tags (acrochordons) | Tiny pedunculated enhancing projection from skin surface |
| Focal skin inflammation | Ill-defined skin enhancement; correlate with clinical history (dermatitis, folliculitis) |
Imaging Appearance
T1-Weighted (Pre-contrast)
- Most skin lesions are isointense to skin or slightly hypointense
- Sebaceous cysts may be T1-bright due to proteinaceous or lipid content
T2-Weighted
- Variable signal; cystic lesions (epidermal inclusion, sebaceous) may be T2-hyperintense
- Solid lesions (moles, keloids) are typically intermediate T2 signal
Post-contrast T1-Weighted (Fat-suppressed)
- Enhancement is the hallmark — the reason these lesions are detected on MRI
- Enhancement ranges from mild to avid depending on vascularity
- Best identified on fat-suppressed early post-contrast T1W images or subtraction images
- Located at the skin surface — confirm on two orthogonal planes to verify dermal origin
Key Localizing Feature
- The lesion is centered within or projecting from the skin, not the breast parenchyma
- On sagittal and axial images, the lesion should be traceable to the skin surface
- If any portion extends into the parenchyma or appears to arise from breast tissue, it should not be classified as a skin lesion
When to Report
- Do not report if imaging morphology is benign and there are no clinical concerns
- Report if there are suspicious MRI morphology features (e.g., spiculated margin, irregular shape, associated parenchymal extension)
- Report if there are known suspicious clinical features (e.g., palpable concern, skin changes, rapid growth) → recommend clinical assessment and correlation
Board Pearl
The default action for enhancing skin lesions is to not report them. Only report when suspicious morphology or suspicious clinical features are present. Overcalling benign skin lesions generates unnecessary workup.
Differential Diagnosis
| Entity | Key Distinguishing Features |
|---|---|
| Benign skin lesion (mole, keloid, cyst) | Skin-based, well-circumscribed, no parenchymal extension, stable |
| Associated Feature — Skin Involvement | Enhancement extends from an underlying parenchymal malignancy into the skin; not an isolated skin lesion |
| Dermal metastasis | History of known malignancy; new, growing skin nodule; may have irregular margins |
| Recurrent carcinoma at skin | Prior mastectomy or lumpectomy; new enhancing nodule in or near surgical scar |
| Inflammatory breast cancer | Diffuse skin thickening and enhancement, not a focal discrete lesion; associated with parenchymal findings |
Board Pearl
An enhancing skin lesion in a patient with prior mastectomy or known cancer history should raise suspicion for cutaneous recurrence (e.g., recurrent invasive lobular carcinoma). BI-RADS v2025 Figure 5 (p. 153) illustrates a skin lesion that proved to be recurrent ILC — clinical context is essential.
Pitfalls
- Misidentifying a superficial parenchymal mass as a skin lesion — always confirm the lesion is centered at the skin surface on two planes; a peripheral mass with skin contact is not a “skin lesion”
- Ignoring enhancing skin lesions in high-risk patients — while most are benign, new enhancing skin nodules in patients with cancer history warrant further evaluation
- Confusing skin involvement with a skin lesion — Associated Feature — Skin Involvement implies tumor extension into the skin from an underlying malignancy and upgrades staging (T4b); an enhancing skin lesion is an independent, benign finding
- Keloids mimicking suspicious enhancement — keloids can be large, irregular, and avidly enhancing; correlate with history of surgery or trauma at that site
- Motion artifact at skin surface — can simulate focal skin enhancement; compare with subtraction images and check for misregistration
Clinical Significance
- Enhancing skin lesions are classified under “Other Findings Typically Benign” in BI-RADS v2025 and do not alter the BI-RADS assessment category
- Reporting benign skin lesions when not warranted contributes to audit inflation and unnecessary clinical follow-up
- The critical management distinction is between an isolated skin lesion (benign, ignore) and skin involvement by tumor (malignant, T4b staging implication)
Board Pearl
Skin involvement (associated feature) = tumor extends into skin = T4b staging. Enhancing skin lesion (other finding) = incidental benign finding = no staging impact. Do not confuse the two — they have completely different management implications.