Slide 2.3
A parathyroid adenoma is composed only of chief cells with no intermixed fat cells. Parathyroid hyperplasia has a similar appearance. Parathyroid adenoma is solitary, involving one single gland. A rim of normal parathyroid gland will be found at the periphery of an adenoma. An adenoma is the most common cause of primary hyperparathyroidism.

Parathyroid hyerplasia classically involves all four glands. A rim of normal parathyroid gland will not be found at the periphery. It is seen in secondary hyperparathyroidism, the most common cause of which is renal failure.