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Myolipoma of the Breast: Mammographic, Sonographic, and Pathologic Correlation

A 63-year-old white woman presented with a 3-month history of a palpable mass of the right breast. On physical examination, the mass was mobile and nontender. Imaging evaluation included a mammogram (Fig. 1) that demonstrated a 3 cm mass located at the 12 o’clock position, 7 cm from the nipple, and ultrasound that showed a mass with both hyperechoic and hypoechoic areas (Fig. 2). The clinical impression at the time of imaging was compatible with a benign lesion, with findings suggesting a fibroadenoma intermixed with adipose tissue. Histopathologic examination of an ultrasound-guided core needle biopsy showed bundles of smooth muscle interspersed with mature adipose tissue (Fig. 3). Features suggestive of a malignant mesenchymal neoplasm, including increased mitotic activity, cytologic atypia, or necrosis, were absent. The histologic features were consistent with a myolipoma. Two weeks later, an excisional biopsy was performed that demonstrated a well-circumscribed, tan, rubbery mass measuring 2.8 cm in greatest dimension. The histology of the excisional biopsy specimen showed a well-demarcated tumor with findings similar to the core needle biopsy, including interlacing fascicles of smooth muscle bundles admixed with islands of adipose tissue. The lesion was sampled entirely for histologic analysis and no ductal elements were present in the mass.