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The parathyroid glands are four nodular structures, typically located on the dorsum of the thyroid at each of its four poles. These glands monitor the serum calcium level and secrete parathyroid hormone (PTH) when it is low.[1] PTH is essential for maintaining calcium homeostasis. Thus, dysregulation of this hormone can lead to various pathologies. Histological examination is an important technique used to evaluate and diagnose these pathologies, such as primary, secondary, and tertiary hyperparathyroidism and parathyroid carcinoma.

The dysfunction of the parathyroid glands is an underlying cause of multiple pathologies. Primary hyperparathyroidism characteristically shows inappropriate PTH secretion from at least one parathyroid gland and is most commonly caused by a single adenoma, but may also be caused by multiple adenomas, hypertrophy of all four parathyroids, or rarely carcinoma.[11] Secondary hyperparathyroidism is characterized by hypertrophy of the parathyroid glands in response to low serum calcium; this may result from vitamin D or calcium deficiencies secondary to insufficient dietary intake, malabsorption, or chronic renal failure (CRF).[14] The parathyroid glands respond by increasing PTH secretion, which leads to hypertrophy of the glands overtime to keep up with the increased demand. Tertiary hyperparathyroidism, on the other hand, is characterized by hyperplasia of the parathyroid gland in response to prolonged hypocalcemia, most commonly secondary to CRF.[14] Hypoparathyroidism is a less common disorder, most commonly resulting from damage to or destruction of the parathyroid gland, for example, after thyroid surgery.[15] Pseudohypoparathyroidism (PHP), on the other hand, occurs when the body develops resistance to PTH, especially in the kidney.[16]