Geographic pathology of thyroid diseases.

The thyroid is one of the organs which demonstrates clearly the influence of extrinsic and especially geographically determined influences in the development of diseases. Endemic goiter and cretinism are the most typical examples. The question as to whether thyroid cancer arises more frequently in goiters that in normal thyroids, cannot be answered definitely as yet. But without doubt, the relative frequency of different types of thyroid neoplasms in goiter areas is not the same as in region without endemic goiter. The most common type of thyroid carcinoma observed in a nonendemic region is papillary carcinoma. Follicular and anaplastic carcinomas, however, are more often associated with goiter. Under the influence of iodine prophylaxis, the relative frequency of the different types of thyroid carcinoma approaches that of these carcinomas in nongoiter regions. The malignant hemangioendothelioma is observed nearly exclusively in some Alpine goiter areas. Since the introduction of preventive measures in Switzerland, its occurrence has diminished progressively. In contrast to endemic goiter, focal thyroiditis and even Hashimoto's disease seem to be on the increase since institution of iodine prophylaxis of endemic goiter. As the development of malignant lymphoma may be related to thyroiditis, a possible increase of such tumors should be considered.