Types

Almost all thyroid adenomas are follicular adenomas. Follicular adenomas can be described as "cold", "warm" or "hot" depending on their level of function. Histopathologically, follicular adenomas 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 (oxyphil) - have the potential for microinvasion.

Papillary adenomas are very rare.

Differential diagnosis

A thyroid adenoma is distinguished from a multinodular goiter

Goitre

A goitre or goiter , is a swelling in the thyroid gland, which can lead to a swelling of the neck or larynx...

 of the thyroid in that an adenoma is typically solitary, and is a neoplasm resulting from a genetic mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 (or other genetic abnormality) in a single precursor cell. In contrast, a multinodular goiter is usually thought to result from a hyperplastic

Hyperplasia

Hyperplasia means increase in number of cells/proliferation of cells. It may result in the gross enlargement of an organ and the term is sometimes mixed with benign neoplasia/ benign tumor....

 response of the entire thyroid gland to a stimulus, such as iodine deficiency

Iodine deficiency

Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet—typically remote inlandareas where no marine foods are eaten—iodine deficiency gives rise to...

.

Careful pathological

Pathology

Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....

 examination may be necessary to distinguish a thyroid adenoma from a minimally invasive follicular thyroid carcinoma.

Presentation

A thyroid adenoma may be clinically silent ("cold" or "warm" adenoma), or it may be a functional tumor, producing excessive thyroid hormone

Thyroid hormone

The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,...

 ("hot" adenoma). In this case, it may result in symptomatic hyperthyroidism

Hyperthyroidism

Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...

, and may be referred to as a toxic thyroid adenoma.

Morphology

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 Thyroid parenchyma. The color ranges from gray-white to red-brown, depending upon

1. the cellularity of the adenoma
2. 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.

Management

Most patients with thyroid adenoma can be managed by watchful waiting

Watchful waiting

Watchful waiting is an approach to a medical problem in which time is allowed to pass before medical intervention or therapy is used. During this time, repeated testing may be performed....

 (without surgical excision) with regular monitoring. However, some patients still choose surgery after being fully informed of the risks. Regular monitoring mainly consists of watching for changes in nodule size and symptoms, and repeat ultrasonography or needle aspiration biopsy

Needle aspiration biopsy

Needle aspiration biopsy , may refer to fine needle aspiration cytology , fine needle aspiration biopsy and fine needle aspiration , is a diagnostic procedure sometimes used to investigate superficial lumps or masses...

if the nodule grows.