Thyroid and Parathyroid

Primary hyperparathyroidism may be due to parathyroid adenoma(s), hyperplasia, or,
rarely, carcinoma. Of these causes, a parathyroid adenoma is by far the most common,
accounting for 90 percent of cases. In almost 2 percent of patients with adenomatous
disease, double adenomas are present. Parathyroid hyperplasia (multiglandular
disease) may be found in nearly 8 percent of patients with sporadic
hyperparathyroidism. The incidence of hyperplasia increases markedly and may be
universal in patients with hyperparathyroidism that occurs in families with multiple
endocrine neoplasia (MEN) type I or II, and in patients with non-MEN familial
hyperparathyroidism. Parathyroid hyperplasia is seldom equal or even symmetrical.
This “unequal hyperplasia,” if misinterpreted by the surgeon, may lead to a mistaken
diagnosis of single versus multiglandular disease. Parathyroid carcinoma, as a cause
for hyperparathyroidism, is exceedingly rare, occurring in less than 1 percent of
. patients with this disease
Differentiation between the causes of hyperparathyroidism is of paramount
importance, because the selection of appropriate surgical treatment depends on it.
This delineation is made primarily by the operating surgeon identifying the pathology
encountered at the time of surgical exploration. A structure that looks like a little
kidney in the neck or mediastinum is virtually pathognomonic for single-gland
disease. Finding multiple enlarged glands somewhat “paler than a normal kidney”
suggests multiglandular disease. The pathologist can be of great help to the surgeon,
and vice versa. Unequivocal histologic identification of the causes of primary
hyperparathyroidism can be difficult without the surgeon's description of the gross
characteristics of all glands. With small biopsy specimens alone of parathyroid
glands, it can be extremely difficult for the pathologist to accurately differentiate
histologically between a truly normal gland, a parathyroid adenoma, or a hyperplastic
parathyroid gland. Our own preference is to avoid taking biopsy specimens of normalappearing
glands and to rely on visual inspection of the remaining glands and the
. histology of the excised abnormality to determine the diagnosis
Normal parathyroid glands contain primarily chief cells, with occasional oxyphil
cells. An adenoma is typically defined as an enlarged parathyroid gland that is made
up of solid sheets of chief cells, oxyphil cells, or varying combinations of both with a
rim of compressed normal parathyroid tissue (Fig. 36-43). This compressed rim of
normal tissue is present in only 20 to 30 percent of parathyroid adenomas. The
histology of parathyroid hyperplasia may be difficult to discern unless the nature of
the other parathyroid glands is placed in context (Fig. 36-44). Histologically, the
presence or absence of parathyroid fat cells has been believed by some authorities to
be of help in the diagnosis of parathyroid hyperplasia; the higher the percentage of fat
cells, as demonstrated by fat staining, the lower the chances of hyperplasia, and vice
. versa
The macroscopic appearance of the parathyroid glands, as visualized by an
experienced parathyroid surgeon, continues to be the most accurate means of
. identifying the various types of parathyroid pathology
PHYSIOLOGY OF CALCIUM HOMEOSTASIS
( Parathyroid Hormone (PTH
In patients with primary and tertiary hyperparathyroidism, the secretion of parathyroid
hormone is abnormal and excessive. In secondary hyperparathyroidism, PTH