Pathology of the parathyroid glands

Abnormalities of the parathyroid glands are the commonest cause of hypercalcaemia and the histopathologist has an important role in classifying the underlying pathological condition. Diagnostic assessment includes confirmation that the tissue removed is parathyroid versus, most commonly, lymph nodes or thyroid, possibly requiring intra-operative assessment, and in hyperparathyroidism, establishing whether excised parathyroid glands represent hyperplasia or neoplasia. The commonest neoplastic diagnosis is of an adenoma, usually single, and ‘atypical adenoma’ and carcinoma are much less common. It is important to distinguish the worrisome histopathological features of atypical adenoma, which if precisely defined has an excellent prognosis, from the frankly malignant features of parathyroid carcinoma. Parathyromatosis, presenting most frequently after previous parathyroid surgery, must be distinguished from dissemination from a carcinoma. Less common lesions include parathyroid cysts, parathyroiditis and rare metastases to the parathyroid glands. The molecular and genetic events underlying parathyroid disease are complex, heterogeneous, overlapping and poorly understood. Newer antibodies, including parafibromin and PGP9.5, have been proposed to be useful in separating adenoma from carcinoma but overlapping patterns occur and clinicopathological assessment remains the yardstick of diagnosis.