Preservation of parathyroid function in thyroid and parathyroid surgery

Sammanfattning: Preservation of normal parathyroid function and calcium homeostasis after operations on the thyroid and parathyroid glands is a difficult assignment in endocrine surgery, and it is crucial to minimise the risks of permanent postoperative hypoparathyroidism. The aim of this thesis was to study the vascular supply of the parathyroid glands and the revascularisation, growth, and function of transplanted parathyroid tissue, in order to add new information about parathyroid preservation.The microcirculation and blood supply of normal, hyperplas~c and adenomatous parathyroid glands were studied with laser Doppler flowmetry in 103 patients during operations on the thyroid and parathyroid glands. In normal parathyroid glands the blood flow was higher compared with that in hyperplastic glands and adenomas. Occlusion of the main trunks of the inferior and superior thyroid arteries reduced the blood flow by 35% and 25%, respectively. The reduction was similar in normal, hyperplastic, and adenomatous parathyroid glands. In 12 patients with single parathyroid adenomas, the increased concentration of parathyroid hormone (PTH) remained mainly unchanged despite appreciable reduction in blood flow. In 16 patients the microcirculation and macroscopic appearance of normal parathyroid glands located anteriorly on the thyroid lobe were analysed before and after dissection for in situ preservation. There was a poor correlation between reduction in blood flow and macroscopic appearance of the glands. Laser Doppler flowmetry (LDF) showed that the disturbed microcirculation often recovered 30-60 minutes after dissection for preservation.Parathyroid tissue obtained from 47 patients operated on for hyperparathyroidism was implanted subcutaneously in athymic mice. The processes of revascularisation, morphology, cell proliferation, and function of normal, hyperplastic, and adenomatous parathyroid tissue were studied at 2 and 4 days and 1, 4, 7 and 12 weeks after transplantation. Vessels were detected by monoclonal antibodies specific for mouse and human endothelial cells. The transplanted tissues were examined by light and electron microscopy and by autoradiography after continuous infusion of tritiated thymidine. The relative amount of viable tissue was assessed with a computer image-analysing program. Graft function was judged by measuring human iPTH in mouse serum.Over 90% of the transplants took and the original structure of the tissue was well preserved. Confluent areas of parathyroid tissue could be seen in 80% of the transplants. The mean loss of viable tissue in all three groups was 45%.Immunohistochemical examination showed ingrowth of vessels from the host into the transplant. The sprouts matured gradually into vessels with thin endothelial linings and capillary fenestrations in adenomatous and hyperplastic transplants but not in transplants of normal tissue.In normal parathyroid tissue the proliferation of parathyroid parenchyma! cells increased only slightly in contrast to the advancing proliferative capacity in adenomatous tissue. In contrast to adenomas, parenchyma! cell proliferative capacity in hyperplastic tissue decreased at 12 week.Concentrations of iPTH were raised at one week in hyperplastic and adenomatous tissue. Twelve weeks after transplantation iPTH concentrations in relation to the amount of transplanted tissue and relative area of viable tissue were comparable in all three groups of transplanted tissue.We conclude that, LDF is a feasible method to study physiological blood flow in human parathyroid glands. Parathyroid blood supply is not as dependent on the inferior thyroid artery as was previously suggested. LDF showed that blood flow recovered in parathyroid glands dissected for in situ preservation and any decision about autografting should be delayed until the end of the operation. Parathyroid transplants re vascularise from host vessels and this is more pronounced and proceeds faster in hyperplastic and adenomatous tissue than in normal transplants. In contrast to nonnal and hyperplastic transplants, adenomatous tissue has a greater and increasing proliferative capacity. The iPTH concentration as an expression of parathyroid function correlates poorly with parenchyma! cell proliferation.