Paramyelia, also known as polymastia, refers to the appearance of additional breast tissue in addition to the normal breast in the anterior chest region. In the 4th week of embryonic development, 8-9 pairs of epithelial cells are partially proliferated in the mammary crest between the axilla and the medial inguinal area on both sides of the ventral midline of the trunk to form the mammary gland primordia. According to the developmental pattern of the parametrium, there are two types of parametrium: complete parametrium and incomplete parametrium. Complete parametrium means that the parametrium has nipples and glands. Incomplete parametrium refers to a nipple without a gland, or a gland without a nipple. Incomplete parametrium without nipple is more common in clinical practice. Parametrial glands are present in approximately 2-6% of women and some cases have a genetic predisposition. Paramammary glands are usually clinically asymptomatic, but in some cases they are not detected until a woman develops symptoms such as distention, pressure or even lactation during pregnancy or breastfeeding. Parammary glands tend to grow along the “breast line” of the body and are often located in the anterior axillary line or caudal to or below the normal breast. Parammary glands are more common in the caudal axilla, but there have been many clinical reports of ectopic glands located outside the “breast line”. The diagnosis of paramammary glands is made by clinical examination, imaging and pathology. The ultrasound image of the parammary gland is similar to that of normal breast tissue, but depending on the main components of the parammary gland, the echogenicity of the image may be strong, low, or intermittent, with poorly defined borders, no envelope, and enhanced posterior echogenicity. The diagnosis of paramammary glands is generally considered to be reliable if the echogenicity is similar to that of normal breast tissue in the subcutaneous fat layer and is located on the crestal line of the breast. The axillary paramammary gland is usually seen as a dense shadow in the axilla with the density of the normal breast gland. The axillary paramammary gland X-ray can be of four types: 1. patch and mass type: patch or mass shadows of different sizes are seen in the axilla, with varying densities, either dense or faint, and the edges are mostly clear; 2. cord and branch type: coarse or thin cord-like dense shadows or staggered disorderly branch-like dense shadows are seen in the axilla, with clear edges; 3. mixed type: a variety of mixed images with uneven densities are seen in the axilla; 4. Low-density fatty type: translucent fatty shadows are seen in the axilla. The patch and mass type is the most common, followed by the striated and branching type. The histological diagnosis of the parammary gland is similar to that of the normal breast tissue, and the lobular structure of the ducts and alveoli is visible microscopically. Like normal breast tissue, the paramammary gland is also regulated by a variety of hormones in the body and can show the same physiological responses as normal breasts at different times, such as painful menstrual cycles and lactation during lactation. Parammary glands can also develop other breast-related diseases such as fibroadenoma, lipoma, lobular tumors and breast cancer. Asymptomatic parametrial glands usually do not require any treatment, but surgery may be considered if there is periodic pain that is unbearable, if the parametrial glands are large and affect the appearance or cause discomfort in the upper extremities, or if there are other suspicious lesions in the parametrial glands.