Laboratory diagnosis of thyroid tumors.

Laboratory procedures available for aid in the differential diagnosis of thyroid tumors include serum hormone measurements, a variety of thyroid scanning procedures, ultrasonography and needle biopsy of the thyroid. Serum calcitonin measurements appear to be highly reliable indicators of the pres­ ence of medullary carcinoma of the thyroid gland. Thyroid scans using isotopes of iodide or technetium, thyroid echography or other non-invasive procedures can identify patients in whom the presence of thyroid carcinoma is unlikely. However, no available procedure short of biopsy and histological identification can positively identify a thyroid mass as a carcinoma. The problem of non-operative diagnosis of carcinoma of the thyroid gland is part of the larger problem of the differential diagnosis of uninodular and multinodular goiter. The thyroid abnormalities that may result in those findings include a thyroid cyst, single or multiple adenomatous nod­ ules, chronic thyroiditis and the several types of thyroid adenomas and carcinomas. It is clear that the single most important source of information needed for resolution of this problem is careful palpation of the thyroid gland and surrounding structures. In many instances, the nature of the thy­ roid abnormality and/or the presence of local or distant metastases makes the di­ agnosis of thyroid carcinoma obvious, and only histological confirmation is needed. In other instances, notably when the clinical finding is a solitary nodule of the thyroid gland, the application of various laboratory procedures may prove of value in helping to identify those patients in whom tissue diagnosis is necessary and those in whom it is not. Before reviewing the laboratory proce­ dures available for the evaluation of such patients, some generalizations concerning carcinoma of the thyroid gland in relation to the problem of uninodular and multi­ nodular goiter may be made. Using the simplest possible classification, there are four types of thyroid carcinoma; papillary, follicular, medullary and ana­ plastic. The varied clinical features, age incidence differences and natural course of these types will not be reviewed here. In post-mortem studies thyroid carcinoma may be found in as many as 2.1 percent of people with clinically normal thyroid glands, and nodular goiter is considerably more frequent.13 Higher incidence rates are found in people with clinically abnormal thyroids. In the surgical literature, the fre­ quency of thyroid carcinoma in single thy­ roid nodules ranges from about 5 to 30