• Mammary stroma (Figure 2):

Mesenchymal lesions of the breast comprise a spectrum of lesions that arise in the stroma of the breast. They include fibro-epithelial, fibroblastic and myoblastic, vascular, lipomatous, neural, myogenic, and osseous tumors. Some of these lesions are fairly common, while other lesions are extremely rare with no known prevalence and only a few cases report in the literature. 

1. Blood vessels (Figure 3)

Haemangiomas are the most common benign vascular tumor of the breast. They typically measure less than 2,0 cm and most commonly they are located in the subdermal or subcutaneous soft tissue. 

2. Nerve (Figure 4)

Schwannomas in the breast are extremely rare. These benign slow-growing neoplasms originate from Schwann cells which form myelin in peripheral nerves.

3. Fat (Figure 5)

Lipomas are benign mesenchymal tumors that are composed of mature adipose tissue. Mammography typically shows a radiolucent mass with no calcification with a thin, peripheral and fluid density capsule. 

4. Muscle (Figure 6)

This tumor accounts for less than 1% of all breast malignancies and less than 5% of all soft tissue sarcoma. 

Mammography can demonstrate an oval, isodense, microlobulated lesion and the ultrasound can reveal a hypoechoic and microlobulated nodule.

• Skin appendages (Figures 7-11):

The skin appendageal tumors encompass a wide variety of tumors clinically presenting as papules and nodules. They are basically classified into four groups: tumors with differentiation towards hair follicles, sebaceous glands, eccrine or apocrine glands. Imaging characteristics can depict skin thickening and retraction, nodule and spiculated mass.

• Thoracic muscle (Figures 12-13):

Myxoid liposarcomas arise from the intermuscular fascial planes or deep-seated areas. It is the second most prevalent type of liposarcoma. A spectrum of MR imaging abnormalities can occur depending on the amount of fat and myxoid material, the degree of cellularity and vascularity, and the presence of necrosis.

• Lymphoid tissue (Figures 14-16):

The isolated manifestation of lymphatic system cancer in the breast is rare and usually present with bilateral lymph nodes enlargement or a breast mass.

• Non-mammary metastasis to the breast (Figures 17-19):

Non-mammary metastases to the breast and axilla are rare occurrences. However, they are important diagnostic considerations as their treatment and prognosis differ significantly from primary breast cancer. The ovary is one of the most common sites of origin for carcinoma.