Infectious mastitis reflects a variety of underlying etiologies. Acute puerperal mastitis is the most common form of mastitis and usually occurs from infection with Staphylococcus aureus or Streptococcus. Periductal mastitis typically occurs in premenopausal women when the ducts beneath the nipple become inflamed and infected. It is unclear if the dilated or ectatic duct produces periductal inflammation or if a dilated duct is in general more prone to inflammation. At US blocked ducts often appear as dilated tubular structures filled with echogenic material and there is often subjacent hiperemia  (Fig. 1) . If the infection is not treated, a retroareolar abscess may occasionally result.

US plays an important role in the diagnosis and treatment of mastitis if abscess formation is suspected. Abscesses usually manifest as irregular hypoechoic or anechoic masses, sometimes with fluid-debris levels and posterior acoustic enhancement (Fig. 2).

Galactoceles are the most common lesions in lactating women and infection is a relative common complication. On ultrasound, it appears as a round hypoechoic to hyperechoic nodule with well-defined margins. Diagnosis is made based on an appropriate clinical picture and aspiration of milky and purulent material from the cyst. (Fig. 3)

Non-infectious mastitis include diabetic mastopathy which is a rare but well-known entity in patients with long-standing insulin-dependent diabetes. It is oftenly multicentric and bilateral. Its clinical and radiological presentation mimics breast malignancy and diagnosis is usually confirmed on histology. It is characterized by a perilobar and perivascular lymphocytic infiltrate, stromal fibrosis, lobular atrophy and characteristic myofibroblastic epithelioid cells. (Fig. 4)

Granulomatous mastitis is a very rare inflammatory disease of unknown origin that can clinically mimic carcinoma. It is seen more frequently in females at a reproductive age. Clinically, it presents as a painful, firm, ill-defined mass in the breast. The diagnosis of granulomatous mastitis is based on exclusion of other granulomatous reactions. Mammography and ultrasound often show non-specific findings that can suggest a malignant disease. (Fig. 5)

Fungal infections, although rare, can affect the breast, inducing a granulomatous reaction that is often indistinguishable from carcinoma. We present a case of breast sporotrichosis in a patient with two painless lumps in the breast closely mimicking malignancy on US. (Fig. 6)

Skin lesions such as epidermal inclusion cysts or sebaceous cysts can also be infected. Radiological findings reveal dermal lesion, often well circumscribed with mixed echogenicity, reflecting varying internal contents (Fig. 7). There may be presence of a tract extending to the skin surface.

Breast inflammation may involve the axillary lymph nodes and cause reactive enlargement. Differentiating benign reactive lymphadenopathy from malignant lymphadenopathy based on imaging features alone can be challenging. We report a case of cat scratch disease presenting as axillary lymphadenopathy (Fig. 8). The bacterium Bartonella henselae causes cat scratch disease, a self-limited zoonotic disease which is common among children and adolescents. The most typical clinical presentation is a regional lymphadenopathy that commonly involves only a single node of cervical and axillary lymph nodes. Often antibiotic treatment is not required because it is a benign disease and often resolves spontaneously.