Describe the appearance and location of a sebaceous cyst on breast ultrasound.

• A. Round or oval well-defined superficial mass near the skin/dermis with low to medium internal echoes and absence of internal blood flow
• B. Deep intramammary mass with strong vascularity
• C. Cyst with posterior acoustic shadowing
• D. Irregular mass with spiculated margins

Answer: (A)

Sebaceous cysts on breast ultrasound are typically superficial lesions located in the dermis just beneath the skin. They usually appear round or oval with well-defined margins and sit close to the skin surface. The keratinous material inside gives low to medium internal echoes rather than being completely anechoic, so you see internal echoes rather than a clear fluid fill. Importantly, there is typically no internal blood flow on Doppler, reflecting the nonvascular nature of a simple cyst filled with keratin debris. This combination of a superficial, well-defined, mostly echogenic lesion near the skin with no internal vascularity best matches a sebaceous cyst.

Deep intramammary masses with strong vascularity point toward solid or malignant/inflammatory processes, not a sebaceous cyst. A cyst with posterior acoustic shadowing could occur, but the defining feature here is the superficial, dermal location with keratin-containing internal echoes and lack of vascularity, which aligns with a sebaceous cyst. An irregular mass with spiculated margins is characteristic of malignancy and does not fit the typical appearance of a sebaceous cyst.