There is a round thing inside the tendon on the left side of the neck which may be related to epidermal cyst, enlarged lymph nodes and myofibroma. Epidermal cyst: a benign swelling of the skin, that is, a cyst containing keratin inside the dermis, extrusion can sometimes be seen white material extrusion, rounded elevated nodules, can slowly increase, when the increase to a certain extent no longer change. Enlarged lymph nodes: Enlarged lymph nodes are usually associated with local tissue inflammation. When the local tissue is infected, the lymph nodes will produce lymphatic fluid containing immune cells to destroy the invading bacteria, viruses, etc., but the enlarged nodes will be left afterwards. Myofibroma: When myofibroma occurs as a result of a lesion in the muscle tissue, it can be felt as a round shape inside the tendon on the left side of the neck. If symptoms such as pain occur, surgery is needed to remove the myofibroma. The left side of the neck tendon inside a round thing may also be related to overstrain, it is recommended to timely visit the hospital to identify the cause of the disease, to give the corresponding treatment and treatment.