The mastoid lymph nodes are part of the lymph nodes in the head, and as the name implies, they are generally located in the mastoid region, the exact location of which is the bony prominence behind the ear. The postauricular mastoid lymph node is located on the superior surface of the sternocleidomastoid muscle behind the ear, also known as the postauricular lymph node, and is mainly a lymph node that organizes the superficial lymphatic vessels in the top of the skull and behind the auricle. Clinically, the mastoid lymph nodes cannot be felt by hand under normal circumstances, but enlargement of the mastoid lymph nodes can occur when the patient has the following conditions. First, inflammatory infections, such as acute otitis externa or acute otitis media, which involve the back of the ear, can lead to enlarged lymph nodes behind the ear. Second, tuberculosis disease, which can lead to enlargement of the lymph nodes in the mastoid area behind the ear. Third, cancer lesions such as middle ear cancer, which metastasizes to the lymph nodes behind the ear, i.e. the lymph nodes in the mastoid area, can also lead to enlarged lymph nodes.