Parathyroid glands in primary hyperparathyroidism: an ultrastructural study of 50 cases

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.

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

In parathyroid glands removed from patients with primary hyperparathyroidism (pHPT), hyperplasias and adenomas cannot be distinguished from one another by light microscopy when only one gland is available for examination. When a second gland is available, it is necessary to establish whether it is normal, suppressed, or hyperplastic. This distinction may be difficult, and the main criterion is the amount of cytoplasmic lipid in the parenchymal cells. If the lipid is abundant, the gland is considered normal or suppressed, and if it is scanty, the gland is interpreted as hyperplastic. We have performed a morphometric ultrastructural study to test the reliability of this criterion. Twenty-five adenomatous glands removed from patients with pHPT, when compared with glands of normal size from euparathyroid patients, showed a significant increase in the parameters indicative of metabolic activity, namely the size of the Golgi apparatus, the amount of rough endoplasmic reticulum, and the length of plasmalemmas. In addition, the amount of cytoplasmic lipid was significantly reduced. Furthermore, 25 glands of normal size removed from the same patients with pHPT showed an amount of lipid similar to that of normal glands from euparathyroid patients. However, all the parameters indicative of metabolic activity were significantly higher than those in glands from euparathyroid patients and comparable to those found in adenomatous glands. These results suggest that in pHPT, normal-size glands are as active as adenomatous glands, regardless of a higher lipid content.

Morphometric evaluation of intracytoplasmic lipid in normal and pathological parathyroid glands

The chief morphological criterion for classifying parathyroid glands as 'normal', 'suppressed', or 'activated' is the lipid content of the cytoplasm. In particular, cytoplasm lipid deposit is scanty in the active parathyroid cell, according to many authors. In this paper we present the results of a morphometrical study of ten normal parathyroid glands from patients undergoing thyroidectomy, 20 enlarged 'adenomatous' glands from patients with primary hyperparathyroidism, and 20 glands of normal size from the same hyperparathyroid patients. We aimed at assessing the content of intracytoplasmic lipid of secretory cells in all these conditions. The results show that secretory cells of adenomatous glands have less lipid than those from normal glands; however, there was considerable overlapping of the data in the two groups. The mean lipid content of cells in glands of normal size taken from hyperparathyroid patients was not significantly different from the mean value of normal cells, even when ultrastructural evidence of activation was present in the former. These data suggest that caution has to be exercised in assessing the functional status of parathyroid glands on the basis of lipid content of secretory cells, mainly when differentiating between adenoma and hyperplasia.

Storage and degradation of secretory proteins in adenomatous and secondary hyperplastic parathyroid cells. An immunoelectron microscope study

Parathyroid hormone (PTH) and chromogranin A/secretory protein-I (SP-I) have been localized on immunoelectron microscopy in double-fixed tissues from adenomatous and secondary hyperplastic parathyroid glands. Storage organelles, identified on the basis of their consistent labelling, included tow morphologically distinct varieties of granules/vesicles; the mature granules and the progranules. The former consisted of dense, mostly rounded, medium to large-sized bodies which were strongly labelled and predominant in the proximity of the cell membrane. The other variety of body included a spectrum of small pale vesicles/granules which were mainly located in the Golgi area. Because their morphology and their labelling pattern varied other bodies were assumed to be engaged in degradation or cleavage of the secretory proteins. These bodies comprised crinophagic structures, that is to say multivesicular bodies and large Golgi-related vesicles, as well as a number of atypical solid bodies. Whereas most of the granulated cells stored a mature or a maturing population of vesicles/granules, the process of maturation appeared to be either absent or incomplete in a number of cells from some glands. The major defects were frequently associated with an unusual labelling pattern of the Golgi area and selectively affected groups of cells from all the transitional oxyphil cell adenomas. The minor defects concerned individual cells of different types present in both categories of glands. The present data suggest that in hyperfunctioning glands, the type of hormone processing depends on the capacity of each cell in progranule maturation and that the maturation capacity may decrease dramatically in adenomatous or chronically hyperstimulated cells of the transitional oxyphil type.

Parathyroid cell variants may be provoked during immersion fixation

Parathyroid glands of cattle, dogs, cats, mice and rats were immersed in glutaraldehyde or mixtures consisting of glutaraldehyde, formaldehyde and acrolein in either Na-phosphate, Na/K-phosphate or Na-cacodylate buffer, and postfixed with OsO4 in the same buffers or, alternatively, in s-collidine. Excellent preservation of bovine, feline and murine parathyroid glands was achieved with fixation mixtures containing 1% glutaraldehyde, 1.5-2% formaldehyde and 2.5-5% acrolein in 0.1 M Na-cacodylate with or without Ca2+ and Mg2+, Na-phosphate or Na/K-phosphate at 4 degrees C followed by postfixation with 1% OsO4 in the same buffers or in s-collidine containing sucrose, Ca2+ and Mg2+. This procedure largely abolished the occurrence of parathyroid cell variants. Bovine parathyroid glands were also satisfactorily preserved with 1% glutaraldehyde and 2% formaldehyde whereas 1% glutaraldehyde and 2.5 or 5% acrolein, lower or higher buffer osmolarity, or immersion at room temperature led to vacuolization of RER and to breakdown of membranes. In contrast, all fixation protocols led to the formation of dark and light cell variants and to multinucleated syncytial cells in dog and rat parathyroids. The results thus show that parathyroid cell variants arise during immersion fixation and that aldehydes, buffers and temperature are important factors for provoking parathyroid cell variants.