Hyperplasia (or “hypergenesis”) is a general term referring to the proliferation of cells within an organ or tissue. Hyperplasia may result in the gross enlargement of an organ, the formation of a benign tumor. Hyperplasia is considered to be a physiological response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. This stands in contrast to neoplasia (the process underlying cancer and some benign tumors), in which genetically abnormal cells proliferate in a non-physiological manner which is unresponsive to normal stimuli.^[1]

• Hyperplasia may be classified into 2 groups:^[2]

Physiologic hyperplasia

• Normal stressor (eg. pregnancy)

Pathologic hyperplasia

• Abnormal stressor (eg. pituitary adenoma)

• The pathogenesis of hyperplasia is characterized by an increase in the number of cells.^[2]
• Hyperplasia is the result of growth factor driven proliferation of mature cells.^[1]
• The pathogenesis of hyperplasia is limited to cells that have the capability of reproduction, excluding primarily myocytes and neurons.
• On gross pathology, findings of hyperplasia will depend on the anatomical site.

• Hyperplasia may be caused by either increased metabolic demand, chronic inflammatory response, or compensation for damage.

• Hyperplasia must be differentiated from other diseases that cause abnormal tissue growth such as:^[2]

• Cancer
• Hypertrophy
• Metaplasia

• Some examples of hyperplasia, include:

• Congenital adrenal hyperplasia
• Endometrial hyperplasia
• Benign prostatic hyperplasia
• Hyperplasia of the breast
• Focal epithelial hyperplasia
• Sebaceous hyperplasia
• Compensatory liver hyperplasia

• Common risk factors in the development of hyperplasia are genetic mutations, chronic inflammation, increased metabolic demand, and hormonal stimulation.^[2]

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