Mastopathic-Type Breast Fibroadenomas Can Have Indistinct Margins on Ultrasound: A Case Report

Fibroadenoma is one of the most common benign breast tumors and exclusively has clear margins regardless of subtypes. We herein report a mastopathic-type fibroadenoma with indistinct margins on ultrasound. A 53-year-old postmenopausal woman with cecum cancer presented with a right breast mass on staging computed tomography (CT) for the cecum cancer. Mammography only suggested the presence of a breast mass and could not contribute to image diagnosis due to the dense breast. Ultrasound showed that the mass had indistinct margins, multiple dotted or linear hyperechoic foci against the background low echoes, and posterior acoustic enhancement. Magnetic resonance imaging (MRI) depicted that the mass had distinct margins and showed low signals on T1-weighted images, high signals on T2-weighted images, and a persistent pattern on subtraction MRI. Core needle biopsy pathologically showed hyperplasia of the ductal epithelium without any malignant findings. The patient, therefore, underwent a lumpectomy of the breast mass during the cecum cancer operation. Postoperative pathological study showed that the oval mass had clear but ruffled tumor borders, many fat cell clusters near the mass edges, stromal cell proliferation, and plentiful glands showing a blunt duct adenosis-like pattern with focal papillomatosis. These pathological findings led us to the diagnosis of mastopathic-type fibroadenoma. Diagnostic physicians should note that mastopathic-type fibroadenomas can have various pathological components of fibrocystic disease and therefore can have indistinct margins on ultrasound.