It may be congenitally absent, variations in size are common, and small accessory glands may occur. Total absence is usually associated with cretinism or idiocy.

Atrophy takes place normally in old age.

Hypertrophy, or goiter, is a condition in which there is hyperplasia of the interstitial or glandular tissues. These enlargements are classified under various headings.

Hypertrophy can be divided into two main varieties: (I) Diffuse and (2) nodular. Both can be subdivided into (a) colloid and (b) parenchymatous forms.

1. In the diffuse variety there is a uniform enlargement, or one lobe may be more enlarged than the other, but it presents no circumscribed nodules differing in structure from the rest of the lobe.

(a) Colloid type. In this the follicles are so greatly distended with colloid material that the walls may rupture. The epithelium is flattened and destroyed. The functioning epithelium being destroyed, and the colloid being nonabsorbable, the symptoms of hyperthyroidism do not appear.

(6) Parenchymatous type. In this there is a glandular proliferation resembling tumor formation. Solid masses and cords of cells similar to the fetal thyroid are present. Colloid material is lacking or scanty. Papillary projections of epithelium into the acini, papillary cystic goiter, may be found. On account of the increase in functioning tissue the symptoms of hyperthyroidism appear.

2. In the nodular variety there are found circumscribed areas surrounded by a connective-tissue capsule. These areas may show colloid or parenchymatous changes. Both forms may be present in the same thyroid. Fatty as well as hyaline changes are common in the nodes. Between these areas the gland tissue may be normal, degenerated, or atrophic. Cysts may arise through the absorption of the walls separating the acini and allowing large accumulations of colloid to form (Fig. 9).

Hyperthyroidism, Graves' or Basedow's disease, exophthalmic goiter, is an enlargement of the gland associated with exophthalmus, palpitation of the heart, tachycardia, tremors of the hands and vasomotor disturbances. The bloodvessels are dilated, interstitial hemorrhages may occur, and these are sometimes followed by necrosis. There is a proliferation of the epithelium of the acini, with a decrease of the colloid material. The symptoms may be due to an excess of iodin formation or of iodin absorption.

The effects of goiter may be local, as a result of the pressure exerted, or distant, on account of some disturbance of nutrition. Its cause is unknown. In certain countries it is endemic, and more common in high altitudes than in low.

It is very commonly associated with cretinism, occurring in about 60 per cent, of such cases.

Hypothyroidism is a condition in which there is a decrease in the thyroid activity. It may be divided into the following forms:

1. Endemic cretinism. Gland shows areas of atrophy and of goitrous degeneration.

2. Sporadic cretinism, due to congenital absence of the thyroid.

3. Infantile myxedema. Acquired loss of perversion of thyroid function in early life.

4. Adult myxedema. Spontaneous diminution in thyroid tissue, with degeneration of the parenchyma and overgrowth of connective tissue.

5. Operative myxedema (cachexia strumipriva). Due to operative removal of the thyroid.

In myxedema there is a marked thickening of the skin, due partly to a tissue resembling granulation tissue, containing an increased number of fibrils and nuclei; partly to an infiltration by an amorphous material, resembling mucus, in the lymph spaces.

Hyperemia occurs in cardiac disease and when there is obstruction to the circulation by tumors. The gland may in consequence be much enlarged. In Graves' disease the gland is very vascular.

Inflammation (thyroiditis) is not common. It may follow traumatism or infection, and varies in its severity. Suppuration may occur with, at times, fatal results. The pus may remain confined within the capsule, and by pressure interfere with respiration. The abscess may perforate the trachea, esophagus, or skin, or it may follow along the cervical fascia into the mediastinum.

Tuberculosis, syphilis, and actinomycosis are very unusual, but have been observed.


Fibromata in the form of circumscribed nodules occasionally occur.

Sarcoma is a common primary tumor of the gland. It occurs in all forms, the round-cell variety being the commonest.

Carcinoma is the commonest form of primary tumor. It begins usually in an adenomatous goiter, and is of the adeno-carcinomatous type. It grows rapidly, soon invades the tissues of the neck, and frequently gives metastases to the lungs, bones of the skull, inferior maxilla, sternum, and the long bones. The metastases may resemble normal thyroid, contain iodin, and may carry on the normal function. Degenerative changes are quite common.

Adenoma can seldom be differentiated from a glandular hyperplasia unless the growth is distinctly circumscribed.