To summarize the sonographic characteristics of breast fat necrosis at different locations, and estimate the diagnostic value of high frequency ultrasound for fat necrosis.

Clinical and imaging data of 63 patients with breast fat necrosis confirmed by surgery were retrospectively analyzed from January 2014 to September 2019 at Beijing Tiantan Hospital, Capital Medical University. The 63 patients with 69 lesions were all examined by ultrasound before operation. According to the location (fat layer, both fat layer and gland, and gland), the lesions were divided to extra-glandular type, junctional type, and intra-glandular type. Ultrasonic features of different types were summarized and compared.

Of the 63 patients, 22 had a history of trauma or surgery and 7 had previous inflammatory lesions. The patients were mostly asymptomatic or the mass was discovered accidentally. According to the location of the 69 lesions in ultrasound images, excluding two missed cases, 31 belonged to extra-glandular type, 26 belonged to junctional type, and 10 belonged to intra-glandular type. There were no statistically significant differences in sonographic findings between the extra-glandular and intra-glandular types (P>0.05). We observed statistically significant differences in some sonographic features between the junctional type and extra-glandular or intra-glandular type, including shape, boundary, blood flow, relationship with adjacent tissues and skin, and enlargement of ipsilateral axillary lymph nodes (P=0.045, 0.001, 0.025, 0.001, 0.01, and 0.019, respectively). There was no significant difference in capsule, echo type, calcification type, posterior echo condition, or the number of lesions among the tree types (P>0.05). Two (2/69, 2.9%) lesions were missed by ultrasound, and five (5/67, 7.5%) were diagnosed as potential malignancies (BI-RADS 4b).

The sonographic and clinical manifestations of breast fat necrosis are diverse. Obtaining sonographic manifestations of lesions in different locations by high frequency ultrasound, inquiring relevant history and associated diseases, especially trauma or surgical history, and acquiring other clinical information are very helpful to make a correct diagnosis of breast fat necrosis.