The single, benign parathyroid adenoma is the most common ab normality in PHPT. Multiple parathyroid adenomas are much less common, with an incidence less than 5%. While double adenomas can be found, it is important to ascertain that the other glands are normal because some of these patients actually have four- gland disease. Even if normal parathyroid tissue has been documented at the time of the parathyroid surgery for double adenomas, there is always the possibility that the patient will in time develop hyperfunction of the remaining parathyroid glands. In these situations, time is the key determinant and, thus, monitoring is highly recommended. Parathyroid adenomas are notoriously variable in location. While they are usually found at the inferior– anterior and superior– posterior poles of the thyroid gland, they can be found almost anywhere in the neck. Some typical ‘hiding places’ for adenomas in ectopic locations include the thyroid gland parenchyma, itself, and the superior mediastinum. In the mediastinum, the gland can be found within the thymus. More unusual locations for ectopic parathyroid glands include the lateral neck, the carotid sheath, behind the oesophagus and even in the oropharynx.
Four- gland parathyroid hyperplasia is present in approximately 15% of patients with primary hyperparathyroidism. While one immediately considers a familial syndrome, in this context, only about 30% of patients will be shown to have the familial form of PHPT. Before localization procedures and surgery, itself, no clinical features raise suspicion for multiglandular disease. Invariably, the pathology of PHPT is benign, overactive tissue with the malignant parathyroid gland found in fewer than 0.5% of patients. In the case of parathyroid cancer, clinical clues are often apparent, such as marked hypercalcaemia and very high levels of PTH, along with a palpable neck mass. The pathological features raise suspicion for malignancy because the tissue may have invaded local tissues and show histological features of cancer. On the other hand, parathyroid cancers can present pathologically as rather benign tissue. Careful examination of the pathological specimen in parathyroid cancer will often show the cardinal features of malignancy, namely tissue invasion and local or distant metastases. Parathyroid cancers pre sent as functional tumours, secreting PTH.
