A lump was found in the lower part of the armpit, and there was obvious pain on pressure. It is more likely to be an axillary parametrium, and further local color ultrasound examination is needed. Parametrium is a very common condition that is a congenital developmental malformation, also known as polymastia. Many patients present with a localized bulging skin mass, which is also known as a combined nipple. This occurs when the breast tissue degenerates during the embryonic period and is left behind. There is also significant pain when the lesion is squeezed on examination. Parametrial disease can also be hyperplastic and may even be malignant. Therefore, if there is significant clinical discomfort, surgical treatment should be chosen, and the lesion can usually be removed under local anesthesia.