What may the surgeon find when doing a parathyroid exploration?
When exploring the neck for parathyroid disease there are six possible findings.
1. Single adenoma - 80% CasesThe surgeon will remove the adenoma and in the traditional approach check all three remaining parathyroids. Rapid (frozen section) pathology is performed on the adenoma to confirm removal of parathyroid tissue. If available, intraoperative parathyroid hormone biochemistry is performed and if both pathology and biochemistry are satisfactory the neck is closed. In the scan directed method only the adenoma is removed if intraoperative biochemistry is satisfactory. This is the most common finding in primary hyperparathyroidism.
Small parathyroid adenoma lying in the neck - click to enlarge
Small parathyroid adenoma (operative specimen) - click to enlarge
Histology of parathyroid adenoma with tumour on the left separated from a rim of normal tissue on the right by a capsule
2. Parathyroid hyperplasia - 16% of cases. Very difficult to deal with. There are two possible courses of action:
a) Remove all parathyroid tissue, check there are not more than four glands and remove the thymus, which so often contains parathyroid tissue (cervical thymectomy). Subject the tissue to frozen section and then there are two options: firstly one can dispose of all the parathyroid tissue, curing the patient but necessitating replacement with calcium and vitamin D pills for life. The second approach is subtle and consists of transplantation of parathyroid tissue (100mgs) into the non-dominant forearm in a muscle pocket. These transplants take well and any spare tissue can be cryopreserved in liquid nitrogen for future use if the transplant fails or is inadequate. Prior to transplantation the tissue must be confirmed to be benign, as transplantation of a parathyroid cancer is a disaster.
Parathyroid transplantation - click to enlarge
Parathyroid transplantation - click to enlarge
b) Remove three glands and leave 125mgs of parathyroid tissue, after checking the parathyroid pathology. In the elderly this is a satisfactory approach. The problem is that after 10 years 50% of patients will develop significant recurrent disease needing a further operation, and in the young this approach is unacceptable.
Multiple hyperplastic glands typical of parathyroid hyperplasia
3. Double adenoma - 2% Cases. This is a rare event and must be differentiated from subtle forms of asymmetric parathyroid hyperplasia (we have commonly found this condition in patients with the MEN1 Syndrome). In true double adenoma both tumours are removed and the normal glands biopsied (with intra-operative PTH sampling if available).
4. Parathyroid cancer - Cancer of the parathyroid is veryrare (1% of all cases). Usually the serum calcium is grossly elevated and there is a hard mass in the neck stuck to the thyroid. The surgery consists of removal of all the local thyroid and parathyroid tissue, attempting not to break into the cancerous tissue. Look for lymph nodes and use intraoperative PTH sampling if available. Postoperative radiotherapy is wise even if it appears that complete removal of the tumour has been achieved.
5. Parathyroid microadenoma - this is exceptionally rare. It is a small parathyroid tumour, so small that it does not exceed the normal parathyroid weight. It is usually found at the second or third exploration when no enlarged glands have previously been found. Treatment is removal of the gland.
6. No parathyroid tissue is found - This is the endocrine surgeon's nightmare. In expert hands irrespectiveof the technique it is a rare event, occurring in 1-2% of explorations. The surgeon must reassess the situation and reevaluate the diagnosis, particularly excluding benign familial hypocalciurichypercalcaemia. Furtherinvestigations shouldbe performed, such as angiography and venous sampling, in the hope of finding the tumour. The patient should enquire about the unit's expertise and if there is any doubt then referral to a specialised unit is mandatory.