The parathyroid adenoma. A histopathologic definition with a study of 172 cases of primary hyperparathyroidism.

There is unanimous agreement that parathyroid adenoma lacks precise histopathologic definition. Likewise, it is generally accepted that hyperplasia may involve the parathyroid glands unequally, causing tumorous enlargement of a single parathyroid gland. On the basis of observations of the histologic features of the normal parathyroid gland and on the accepted definition of an adenoma, and based on the concept of unequal or "focal" hyperplasia, histopathologic criteria for the recognition of adenoma and its differentiation from hyperplasia were formulated. Study of 172 cases of primary hyperparathyroidism with the use of these criteria showed that adenomas accounted for only 5.8% of cases of primary hyperparathyroidism and that hyperplasia with single gland enlargement accounted for 75.1%. The literature and data supporting the view that solitary masses of the parathyroid glands more often represent hyperplasia than adenoma are cited.