Parathyroid glands in primary hyperparathyroidism: an ultrastructural morphometric study of 25 cases

Atypical Fat Staining Patterns in Hyperparathyroidism

Intracytoplasmic lipid content reflects the metabolic state of parathyroid cells, and staining for this is a useful adjunct in the evaluation of parathyroid glands excised in the treatment of hyperparathyroidism. The procedure, however, is not without limitations, as the unexpected presence of lipid in abnormal, hyperfunctioning glands or its absence in normal glands is occasionally encountered. In this study, the authors review the oil red O staining patterns of 524 parathyroidectomy cases to determine the validity of the stain as well as possible clinical and pathologic correlations. Twenty-seven cases (5.2%) were identified with problematic oil red O staining on which adequate clinical follow-up and pathologic material were available for review. Mean follow-up time was 32 months for this subgroup. The most common problem was the presence of lipid within adenomas (19 cases) or hyperplastic glands (6 cases). Markedly decreased or absent lipid in normal, adenoma-associated glands was seen in two cases. The intensity and distribution of lipid staining in hyperfunctioning glands varied. In four cases, 2/19 adenomas and 2/5 hyperplasia, diffuse positivity, similar to normal parathyroid, were observed. If weak or only focally strong staining patterns are considered to be consistent with hyperfunctioning glands, only six cases, two adenomas, two hyperplasias, and two normal glands could not be resolved. Oil red O stain is useful in diagnosing abnormally functioning parathyroid glands, and, if attention is paid to the staining pattern, few atypical patterns are encountered. Int J Surg Pathol 3(3):163-168, 1996

The role of hyperplasia in multiple parathyroid adenomas

BACKGROUND

Parathyroid adenoma is the most common cause of primary hyperparathyroidism (pHPT). Adenomas usually involve only a single gland, and the remaining glands are normal or suppressed. Multiple parathyroid adenomas have been reported to occur in as high as 11% of patients with pHPT. The significant incidence of multiple adenomas with histologic similarities to hyperplasia has raised the possibility that adenoma is a continuation of the hyperplasia state. To test this theory, we used molecular genetics to compare clonality and proliferative activity of parathyroid adenoma with its corresponding normal glandular tissue. Furthermore, we devised a scheme to definitively distinguish between the different parathyroid states on a molecular level, because histologic distinction is unreliable.

METHODS

The study included three patients with a diagnosis of singular parathyroid adenoma and three with double parathyroid adenomas. Paraffin-embedded surgical specimens of both adenomas and normal glands were retrieved from each patient. Clonal analysis of the phosphoglycerolkinase (PGK) gene has suggested that parathyroid adenomas are monoclonal. Clonality of parathyroid adenomas and normal parathyroid glands was studied by polymerase chain reaction-based restriction fragment length polymorphic analysis for the PGK gene. Proliferative activity of the specimens was also analyzed using the immunohistochemical markers PCNA and Ki-67.

RESULTS

All adenomas were monoclonal and all normal parathyroid glands were polyclonal for the PGK gene in both the single and double adenoma specimens. All adenomas stained positive for proliferative activity. In the three patients with singular adenoma, proliferative activity was not detected in the normal parathyroid tissue. However, in the double adenoma group, two of the three patients showed hyperproliferative activity in the normal glands.

CONCLUSION

Proliferative activity consistent with hyperplasia was present in some normal glands of multiple adenoma patients. Our observation supports the theory that multiple adenomas may be a continuation of the hyperplasia state.

Growth and function of human parathyroid tissue transplanted to athymic mice

The morphology, cell proliferation and function of transplanted normal, hyperplastic and adenomatous human parathyroid tissue was studied after transplantation to athymic mice. The iPTH was evaluated in relation to morphology. Human parathyroid tissue collected during surgery for hyperparathyroidism was implanted subcutaneously into athymic mice (nu/nu-BALB/cA) and was analysed 1, 4, 7 and 12 weeks after transplantation. The transplants were examined by light and electron microscopy and by autoradiography after continuous infusion of 3H-thymidine. The relative amount of viable tissue was evaluated using a computer image analysing programme. Graft function was evaluated by measuring human iPTH in mouse serum. A transplant take ratio of 93% was observed. The proliferation rate in adenoma grafts at 12 weeks after transplantation was five and fifteen times that observed in normal and hyperplastic transplants, respectively. In normal and adenoma groups, a continuous increase in iPTH concentrations was observed, but in the hyperplastic group the iPTH remained on the same level. The secretion of iPTH in relation to the amount of transplanted tissue and the fraction of viable tissue was at the same level at 12 weeks in normal and adenomatous grafted animals. In conclusion, human parathyroid tissue was successfully transplanted and maintained its original structure. The growth potential, but not the iPTH secretion, was significantly higher in adenoma grafts compared to grafts from hyperplastic and normal glands.

Ultrastructure of human parathyroid cells in health and disease

Parathyroid glands (n = 271) removed from 130 patients were examined by light and electron microscopy. A standardized method of tissue processing was employed and morphometry was performed. The aim of the paper is to provide a description of the human parathyroid chief cell ultrastructure in health and disease, with quantitative evaluation of structures involved in secretion of parathyroid hormone in a large case series, and to discuss their role in current diagnostic histopathology. The patients were euparathyroid (n = 10), or affected by primary (n = 97), secondary (n = 8), or tertiary (n = 15) hyperparathyroidism. In normal glands, solid parenchyma was composed of chief cells, large clear cells, transitional-oxyphil cells, and oxyphil cells. Chief cell hyperplasia, pseudo-adenomatous hyperplasia, adenoma, water-clear cell hyperplasia, and carcinoma were the most usual forms of parathyroid disease responsible for primary hyperparathyroidism. In chief cell hyperplasia, all the parathyroid glands were enlarged and the chief cells were in an active state of hormone secretion, with a large Golgi complex, abundant rough endoplasmic reticulum (RER), small lipid droplets, and tortuous plasma membrane. In pseudo-adenomatous hyperplasia, one gland was enlarged and the others displayed a normal size; however, electron microscopic examination and morphometric analysis showed that all the glands had active cells. Adenomas displayed a pattern similar to those of pseudo-adenomatous hyperplasia, with one gland enlarged and the others of normal size. However, ultrastructural examination and morphometry showed that the normal-size glands were hypo-active. Water-clear cell hyperplasia showed cells filled with cytoplasmic vacuoles. In these cells, structures with intermediate features between secretory granules and vacuoles were visible. Nucleo-cytoplasmic atypias were frequently visible in parathyroid carcinoma cells. In secondary and tertiary hyperplasia, active chief cells were regularly mixed with oxyphil or transitional-oxyphil cells. The tertiary hyperplasia was characterized by RER-associated structures that were not found in the normal or other pathological conditions. These results demonstrate that electron microscopy and morphometry represent useful tools in parathyroid histopathology.

Immunolocalization of Parathyroid Hormone in Human Parathyroid Glands with Special References to Microwave Antigen Retrieval

The subcellular localization of parathyroid hormone (PTH) in the normal human parathyroid glands with particular reference to microwave antigen retrieval was investigated using peroxidase-labeled PTH antibody, immunohistochemical, and immunoelectron microscopic methods. The results revealed that PTH granules existed mainly as pro-PTH on the trans side of Golgi and in the regions adjacent to Golgi apparatus. Only a small proportion of secretory granules were stored near the plasma membrane. Microwave irradiation was essential for the immunodetection of PTH. As the irradiative time extended from 1 to 30 min, the staining intensity increased, and the subcellular preservation decreased. Microwave irradiation for 15 mm (with the sections in citrate buffer) with a power output of 500 W is the most ideal for PTH antigen retrieval, as well as for subcellular preservation.

Ultrastructural pathology of parathyroid glands in hyperparathyroidism: a report of 69 cases

The ultrastructural features of 69 parathyroid glands from 43 patients with hyperparathyroidism were studied to distinguish between different parathyroid lesions causing hyperparathyroidism. Samples came from 44 cases of hyperplasia, 21 of adenoma, 3 of carcinoma, and 1 from a histologically normal gland. To establish the diagnosis we took into account intraoperative findings during surgery as well as light microscopic examination. Ultrastructural features, evaluated on a semiquantitative scale, were correlated with diagnostic, clinical, and biochemical parameters. Neoplastic glands were heavier than nonneoplastic ones, and carcinomatous glands were heavier than adenomatous glands. Our findings suggest that the cellular membrane of adenomatous glands shows more folding than that of hyperplastic glands, mainly in the capillary pole. Carcinomatous glands show the greatest degree of irregularity, with the formation of microvilli-like projections. Hyperplastic glands, in turn, are richer in glycogen deposition. Secretory granules appear in higher amounts when the serum calcium level is high. These findings are not of diagnostic value by themselves, but they can be taken in consideration to aid in differential diagnosis.