Adenoma: a benign tumour of the parathyroid glands with a gender ratio of 3F:1M, mostly affecting patients aged 40-60 years. Very rarely may arise in Multiple Endocrine Neoplasia syndromes 1 and 2. Usually only one gland is affected and it may be located either in the neck or at an ectopic site. Usually a tan-coloured circumscribed nodule; large tumours may be cystic. Microscopically, it is composed of chief cells in cords and nests with occasional gland-like structures; neoplastic chief cells are larger than their normal counterparts. Variable numbers of oncocytic cells are present in clusters. Nuclear pleomorphism is common and is probably a degenerative phenomenon. Fibrosis is not common but may be present if there has been previous haemorrhage. Correlation of surgical and pathological findings is required to distinguish adenoma from hyperplasia; the presence of one enlarged gland usually signifies an adenoma. A rim of compressed normal or atrophic parathyroid tissue may be seen in around 50% of cases but is less commonly seen in larger lesions.
"Double adenoma": very rare and requires the presence of two enlarged glands (each weighing more than 70 mg) and two normal-sized glands; MEN 1 syndrome; may be impossible to distinguish from hyperplasia.
Variants include microadenoma (< 6 mm diameter), oncocytic adenoma, lipoadenoma.
Carcinoma: a rare cause of primary hyperparathyroidism. Patients are usually older than those with adenomas and often have very high levels of parathormone secretion. Usually pale, solid tumour; may be encapsulated but often infiltrates adjacent soft tissues. Microscopically, the lesion is composed of chief cells arranged in a solid or trabecular pattern with thick fibrous bands, numerous mitotic figures and capsular invasion but these changes may also be present in a proportion of adenomas. Invasion of nerves, blood vessels and adjacent soft tissues are more reliable features of malignancy. Local recurrence and hypercalcaemia are the main problems; metastasis to lymph nodes or to lung and liver occur in a third of cases.
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