Colloid goiter is histologically distinct from nontoxic nodular goiter, but it may be closely related etiologically. For this reason, it is discussed briefly at this point. It occurs occasionally as a diffuse enlargement of the thyroid gland in adolescent girls, and is especially frequent in this age group in endemic goiter areas. It occurs much less frequently in adults. Typically, the goiter is asymptomatic. It occasionally causes dysphagia or dyspnea, but it is rare for a colloid goiter to produce significant compression of the trachea or esophagus. The gland is usually symmetrically enlarged and feels soft or spongy.
On gross inspection the excised gland is reddish-tan or pale tan in color and homogeneous on the cut surface. On histologic section, the parenchyma is seen to be nonnodular and composed of uniform follicles filled with colloid. The follicles may be of normal size, in which case it must be considered that an increase in the number of normal follicles has produced the increased bulk of the gland, or the follicles may be uniformly distended to several times the usual diameter. Fibrosis and lymphocyte infiltration are not prominent.
The cause of the condition is unknown. In the past it has been ascribed to the intermediate phase of the Marine cycle i.e. between the hyperplastic stage and the multinodular (end) stage of the thyroid gland as described above. More recent studies in mice suggest that such goiters can be induced in animals by TSH without a prior hyperplastic phase.13,89 The stimulus to TSH secretion in these patients may be an increased requirement for thyroid hormone, possible associated with puberty or pregnancy, a period of decreased iodide intake, or the presence within the thyroid of a biochemical lesion interfering with the normal synthesis of thyroid hormone.
The small colloid goiter of adolescent girls may disappear over 1-3 years. On the other hand, it may grow gradually and evolve into the nontoxic multinodular goiter found in adults.
A diagnosis of colloid goiter cannot be made with certainty without histologic confirmation. Thyroid function tests are variable, but the results are frequently normal. Antithyroid antibodies are absent if Hashimoto's thyroiditis is not present. Needle biopsy will confirm the diagnosis but is seldom warranted.
Reassurance that the lesion is not a malignant neoplasm, and that the thyroid is not overactive, is often the only therapy required. If the goiter is large, thyroid hormone may be given in an attempt to decrease its size. If one accepts the theory that the goiter has grown in response to a need for more thyroid hormone, it is logical to expect that exogenous thyroid hormone would cause it to decrease in size. Unfortunately, practice does not always bear out the theory. Only about 70%71 of patients will respond with complete or partial regression of goiter. If there are significant pressure symptoms or if the goiter is a serious cosmetic problem, administration of 131I or surgical resection may be indicated. Subsequent replacement therapy with T4 will be then necessary.