Distinguishing breast skin lesions from superficial breast parenchymal lesions: diagnostic criteria, imaging characteristics, and pitfalls.

Superficial lesions are commonly encountered in the breast and may be located in the dermis, hypodermis (subcutaneous fat), or parenchyma. The differential diagnosis varies for each anatomic layer. Dermal lesions that are seen by breast imagers are usually benign skin cysts. Hypodermal lesions, although usually benign, may include lesions that arise from anterior terminal duct lobular units and include papilloma, adenosis, fibroadenoma, and breast cancer. To avoid misclassifying a small superficial breast cancer as a benign dermal lesion, it is necessary to understand superficial breast and skin anatomy and the mammographic, ultrasonographic (U.S.), and magnetic resonance (MR) imaging signs that indicate that a lesion is dermal. Mammography is the optimal modality for localizing calcifications to the dermis or hypodermis. However, U.S. typically has higher resolution for localizing masses than mammography and MR imaging. At US, a lesion may be categorized as dermal (a) if it is contained entirely within the dermis, (b) if a tract that extends from the lesion to the skin is seen, or (c) if a claw of tissue surrounding the margin of the lesion is present. As with other breast lesions, suspicious imaging features should be sought in addition to determining the anatomic origin. If histologic analysis is necessary to characterize lesions with an unknown cause or origin, precautions must be taken to decrease patient morbidity.