Mastitis occurs relatively often during lactation, specifically in up to 20%-25% of breastfeeding women [15]. The most common pathogens are Staphylococcus aureus and Streptococcus , which are present in the infant’s nasopharynx and infect the breast through nipple cracks during breastfeeding [4]. If an abscess is suspected, ultrasonography is the most useful modality for the diagnosis and treatment of mastitis [1,4]. On ultrasonography, mastitis appears as an ill-defined area of altered echotexture, usually with hypoechoic or heterogeneous echogenicity; increased vascularity is observed on color Doppler ultrasonography (Fig. 3). Ancillary findings include skin thickening and enlarged axillary lymph nodes [2]. The abscess is an irregular hypoechoic or anechoic mass, sometimes with internal echogenic debris and/or posterior acoustic enhancement (Fig. 4) [6]. Treatment of mastitis includes appropriate antibiotic therapy. Ultrasound-guided fine-needle aspiration, vacuum-associated biopsy, or surgical drainage can be effective treatment options in the case of abscess formation [15,16]. However, if the patient does not respond to antibiotic therapy for puerperal mastitis, the possibility of cancer should be considered and further evaluation should be performed [2,4].

Granulomatous mastitis is a rare inflammatory disease of unknown etiology that typically affects young women within 5 years of pregnancy [1,6]. Clinically, it manifests as a firm to hard mass and is accompanied by reactive lymphadenopathy in up to 15% of patients [1,2]. On ultrasonography, solitary or multiple clustered, circumscribed, or irregular heterogeneous hypoechoic masses are observed, often with contiguous tubular configurations (Fig. 5). Diffuse abscess or fistula formation can also be seen [13]. These masses can occur in any part of the breast but tend to spare the subareolar regions [1,2]. Due to the variations in imaging results, they can sometimes resemble malignancy. It is important to correlate the imaging features with the histopathological findings and to engage in long-term follow-up [13].

Galactocele is a milk-filled retention cyst caused by the obstruction of the lactiferous duct. It is the most common benign breast mass in women who are or who recently stopped lactating [6,10]. Clinically, it manifests as one or multiple painless palpable masses [10]. On mammography, galactocele can exhibit various imaging features depending on the proportion of fat and protein in the individual’s breast milk. When completely radiolucent with a relatively high fat content, it is known as pseudolipoma. A cystic mass with a fat-fluid level is a diagnostic indicator of a galactocele, with the fat content above and the water content remaining at the bottom. Alternatively, when the high viscosity of breast milk does not allow the separation of the fat and water contents, a galactocele can resemble a hamartoma; this condition is known as pseudohamartoma [1,4,10]. On ultrasonography, galactocele manifests as a simple or complicated cyst, typically an oval-shaped mass with a circumscribed margin and variable internal echogenicity (Fig. 6) [1,10,17]. A common complication of galactocele is infection. Galactocele infection is confirmed when mixed milky and purulent material is obtained by fine-needle aspiration. On ultrasonography, an infected galactocele appears relatively conspicuous and similar to an abscess (Fig. 7) [1]. Uncomplicated galactoceles with typical imaging features are self-limiting; in cases of galactoceles with associated symptoms or atypical imaging features, ultrasound-guided fine-needle aspiration should be performed [10].

A lactating adenoma is a benign tumor that develops in response to physiological hormonal changes during pregnancy and lactation [10]. Histopathologically, lactating adenomas display lobular expansion with numerous enlarged and dilated acini separated by connective tissue. Lactating adenoma has been suggested to be a variant of fibroadenoma, tubular adenoma, or lobular hyperplasia [6,10], and it can spontaneously regress after pregnancy and lactation [10]. On ultrasonography, lactating adenomas usually manifest as oval, circumscribed, homogeneous, hypoechoic or isoechoic masses and/or posterior acoustic enhancements (Fig. 8A, B). However, lesions with atypical imaging features such as irregular margins, heterogeneity, or posterior acoustic shadowing may mimic malignancy [1,10]. Lactating adenomas can regress naturally upon cessation of pregnancy or lactation (Fig. 8C) [4].

Fibroadenomas are the most common benign breast tumors in young women. The image features of fibroadenomas are usually similar in pregnant and non-pregnant woman [2]. However, morphological and physiological changes can occur during pregnancy and lactation. As hormone-sensitive tumors, fibroadenomas often become enlarged with or without increased vascularity during pregnancy and lactation, and they can regress after the cessation of breastfeeding [1,13]. Spontaneous infarction of fibroadenoma is very rare, but can sometimes occur during pregnancy or lactation. Infarction can cause a fibroadenoma to exhibit more complex features, such as lobulated margins, heterogeneous echotexture, and posterior acoustic shadowing [1,4]. Secretory hyperplasia can sometimes occur in fibroadenomas during pregnancy and lactation. Fibroadenoma with secretory hyperplasia or lactational changes can exhibit heterogeneous echotexture and/ or dilated ducts and cysts, resembling a complex fibroadenoma (Fig. 9) [1]. In cases with atypical radiological features, percutaneous core needle biopsy should be performed to confirm the diagnosis.

Breast cancer that occurs during pregnancy or within 1 year of delivery is defined as PABC. PABC occurs in one of every 3,00010,000 pregnancies and accounts for 1%-3% of all breast malignancies [4,5]. PABC usually manifests as a painless, palpable mass. Because of the difficulty in carrying out clinical examinations during pregnancy and shortly afterward, diagnosis may be delayed [2,4]. PABCs are biologically aggressive and have been found to be larger and more advanced than non-PABCs in same-age patients [2,5]. More than 50% of patients present with axillary lymph node metastasis; additionally, a high prevalence of hormone-receptornegative and HER2/neu-positive tumors has been reported in PABC, as has a high rate of inflammatory breast cancer [1,12,18] (Figs. 10, 11). A combination of delayed diagnosis and an aggressive growth pattern due to the biological effects of pregnancy results in poor prognosis; recurrence is common and appears within 2-3 years of diagnosis [1,2,13]. The imaging features of PABC are similar to those of non-PABC. The sensitivity of mammography is relatively low in pregnant or lactating patients due to increased glandular density; however, mammography may still be useful to visualize malignant microcalcifications, multifocality, multicentricity, or bilaterality [6] (Fig. 12). Ultrasonography is the most appropriate modality to assess PABC [1,12]. On ultrasonography, PABC manifests as a circumscribed to spiculated, hypoechoic to complex mass with or without posterior acoustic shadowing. However, aggressive tumors can show posterior acoustic enhancement that reflects necrotic or cystic degeneration. Associated features include thickening of the Cooper’s ligaments, edema, skin thickening, and axillary lymphadenopathy [2]. On MRI, features of PABCs include circumscribed to irregular margins, heterogeneous or rim enhancement, segmental distributed non-mass enhancement, and diffuse unilateral enhancement [19]. Despite the increased background parenchymal enhancement and T2 signal heterogeneity during pregnancy and shortly afterward, MRI may be a reliable modality of evaluating the extent and severity of PABC (Fig. 13) [5,19,20].