Hyperplasia versus adenoma in endocrine tissues: are they different?

The traditional view holds that hyperplasia of endocrine glands is secondary to oversecretion of a trophic hormone. However, in most cases, the mechanism underlying this growth is the spontaneous proliferation of benign neoplasias. Pathologists still depend on subtle morphological criteria to delineate and further classify these tumours. Owing to their variable architecture, a bewildering nomenclature has emerged for these tumours, exemplified by the many names applied to the goitrous thyroid gland: hyperplasia, adenomatous goitre, adenomatoid nodules, benign nodular thyroid disease, adenoma, etc. This article reviews the evidence suggesting that: (1) the varied types of benign neogeneration of endocrine tissue, the spectrum of which ranges from 'simple hyperplasia' to 'true adenoma', involve the same process; (2) even clonality of a growing lesion cannot distinguish hyperplasia from neoplasia; and (3) the basic processes in both cases are not different from those that cause benign tumours in other organs.