Causes of a round thing growing inside the neck include enlarged lymph nodes, thyroid tumor, lipoma, dermatofibroma, etc. Treatment includes medication and surgery. 1. Enlarged lymph nodes: In case of lymphadenitis, the inflammatory factor stimulates the lymph nodes and causes them to be enlarged, which leads to the phenomenon of a round object growing inside the neck. 2. Thyroid tumor: If it is thyroid tumor, the thyroid gland will be enlarged due to many factors, and a round thing will appear after protruding out of the skin. 3. Lipoma: When fat cells proliferate in large numbers, a round shape may appear on the inside of the neck. 4. Dermatofibroma: Due to the abnormal proliferation of fibrous tissue, a round lump can also appear on the neck. There may be other reasons for the phenomenon of a round thing growing inside the neck, please consult a doctor in time and do the relevant examination, clear diagnosis and symptomatic treatment. The use of the above medications should be strictly in accordance with medical advice.