Thyroid adenoma

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). In this case, it may result in symptomatic hyperthyroidism, and may be referred to as a toxic thyroid adenoma. Thyroid follicular adenoma ranges in diameter from 3 cm on an average, but sometimes is larger (up to 10 cm) or smaller. The typical thyroid adenoma is solitary, spherical and encapsulated lesion that is well demarcated from the surrounding parenchyma. The color ranges from gray-white to red-brown, depending upon the cellularity of the adenoma the colloid content. Areas of hemorrhage, fibrosis, calcification, and cystic change, similar to what is found in multinodular goiters, are common in thyroid (follicular) adenoma, particularly in larger lesions. Almost all thyroid adenomata are follicular adenomata. Follicular adenomata can be described as "cold", "warm" or "hot" depending on their level of function. Histopathologically, follicular adenomata can be classified according to their cellular architecture and relative amounts of cellularity and colloid into the following types: Fetal (microfollicular) - these have the potential for microinvasion. These consist of small, closely packed follicles lined with epithelium. Colloid (macrofollicular) - these do not have any potential for microinvasion Embryonal (atypical) - have the potential for microinvasion. Hürthle cell adenoma (oxyphil or oncocytic tumor) - have the potential for microinvasion. Hyalinizing trabecular adenoma Papillary adenomata are very rare. 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.