A thyroi adenoma, or solitary thyroid nodule is a benign tumor of the thyroid gland. A thyroid adenoma is distinguished from a multinodular goiter of the thyroid in that an adenoma is typically solitary, and is a neoplasm resulting from a genetic mutation (or other genetic abnormality) in a single precursor cell. In contrast, a multinodular goiter is usually thought to result from a hyperplastic response of the entire thyroid gland to a stimulus, such as iodine deficiency. A thyroid adenoma may be clinically silent, or it may be a functional tumor, producing excessive thyroid hormone. In this case, it may result in symptomatic hyperthyroidism, and may be referred to as a toxic thyroid adenoma. Careful pathological examination may be necessary to distinguish a thyroid adenoma from a minimally invasive follicular thyroid carcinoma.