Magnetic resonance suggests a small cystic lesion of the right humerus, and possible diseases include right humeral head cyst and medial epicondylitis of the humerus. 1. Right humeral cyst: this disease refers to the cystic lesion that grows in the right humerus bone, because of its internal bone loss, which triggers the internal osteolytic change of humerus, and its osteolytic area has a large amount of liquid or gelatinous material, and there is a layer of bone cortex surrounded by the outside, and the magnetic resonance examination will find that there are cystic change-like changes. Right humeral cysts are benign lesions. 2. Right medial epicondylitis of humerus: Early stage usually has no special changes on magnetic resonance imaging. If the treatment is not timely or the condition is serious, resulting in localized suppurative infection, liquefied cystic lesions can be found on imaging. In addition, lesions such as right humeral osteoarthritis and osteomyelitis of the humerus can cause these conditions. Small cystic lesions of the right humerus usually do not require treatment if they are small and asymptomatic. However, if there is swelling, pain and gradual increase in size, it is important to consult a doctor to find out the cause of the disease and receive timely and regular treatment under the guidance of the doctor.