A thyroid adenoma is a benign tumor of the thyroid gland, that may be inactive or active (functioning autonomously) as a toxic adenoma. A thyroid adenoma may be clinically silent ("cold" adenoma), or it may be a functional tumor, producing excessive thyroid hormone ("warm" or "hot" adenoma). Can I call symptoms vary from mild to severe hyperthyroidism. Irregular heart rhythm, atrial fibrillation are common symptoms. Toxic adenoma can be surgically removed in younger patients, while in older patients radioactive iodine is used.