There is a small pit behind the ear, and clinically there are the following possibilities: the first possibility is that this pit is present from birth, and many patients find a small pit behind the mastoid process at birth, which may be related to the local mastoid bone protrusion that leads to the formation of the depression below. The second possibility is that some patients have inflammation of the mastoid lymph nodes behind the ear or lymph node disease, resulting in the protrusion of the lymph nodes and the formation of a small pit under the lymph nodes after the protrusion. It is recommended to improve the ultrasound examination behind the ear to roughly determine the nature of the lymph nodes and to check whether there are diseases in the ear canal, around the ear, or the parotid gland that cause the lymph nodes to swell, and to actively search for the cause of the disease to see if the lymph nodes are inflamed or if other causes cause the lymph nodes to swell and form small pits. For other diseases, some patients, for example, have a history of previous surgery and form small pits, and if there is no discomfort, observation is sufficient.