almost always solitary, may lie in close proximity to the thyroid glands, or in an ectopic site
- well-circumscribed, soft, tan to reddish-brown nodule invested by a delicate capsule
- glands outside the lesion are usually normal in size or somewhat shrunken d/t feedback inhibition
parathyroid adenoma
uniform, polygonal chief cells with small, centrally placed nuclei
- at least a few nests of larger oxyphil cells are present
- may resemble Hurthle cell tumors in the thyroid
- a rim of compressed, nonneoplastic tissue, generally separated by a fibrous capsule, is often visible at the edge of the lesion
parathyroid adenoma
may occur sporadically, or as a component of MEN syndrome
- although classically all 4 glands are involved, there is frequently asymmetry with apparent sparing of one or two glands, making distinction from adenoma difficult
- most common macroscopic pattern is chief cell hyperplasia, which may involve the glands in a diffuse or multi-nodular pattern
- there can be islands of oxyphils, and poorly developed fibrous strands may envelop the nodules
primary hyperplasia
may be circumscribed lesions that are difficult to distinguish from adenomas, or may be clearly invasive neoplasms
- these tumors enlarge on parathyroid gland and consist of gray-white, irregular masses that sometimes exceed 10gm in weight
- cells are usually uniform and resemble normal parathyroid cells
- are arrayed in nodular or trabecular patters
- mass is usually enclosed by a dense, fibrous capsule
parathyroid carcinoma
what is the only reliable diagnostic criteria for parathyroid carcinoma?
invasion of surrounding tissue and metastasis
- diagnosis based on cytologic detail is unreliable
what manifests as these three inter-related skeletal abnormalities:
- osteoporosis (especially the phalanges, vertebra, femur)
- brown tumors
- osteitis fibrosa cystica
primary hyperparathyroidism
what is dissecting osteitis?
osteoclasts tunnel into and dissect centrally along the length of the trabeculae, creating the appearance of railroad tracks
- the marrow spaces around the affected surfaces are replaced by fibrovascular tissue
bone loss seen in hyperparathyroidism predisposes to microfractures and secondary hemorrhages that elicit an influx of macrophages and ingrowth of reparative fibrous tissue, creating a mass of reactive tissue known as what?
brown tumor
- brown color is result of vascularity, hemorrhage, and hemosiderin deposition
- not uncommon for lesions to undergo cystic degeneration
what is generalized osteitis fibrosa cystica (von Recklinhausen disease of bone)?
the combination of increased osteoclast activity, peritrabecular fibrosis, and cystic brown tumors
- is the hallmark of severe hyperparathyroidism
what favors the formation of urinary tract stones as well as calcification of the renal interstitium and tubules (nephrocalcinosis)
PTH-induced hypercalcemia
what causes hypercalcemia when PTH is elevated?
- hyperparathyroidism (1, 2, and 3)
- familial hypocalciuric hypercalcemia
what causes hypercalcemia when PTH is low?
- hypercalcemia of malignancy
- vitamin D toxicity
- immobilization
- thiazide diuretics
- granulomatous disease
hyperplastic glands contain an increased number of chief cells, or cells with more abundant, clear cytoplasm (water-clear cells) in a diffuse or multinodular distribution
- fat cells are decreased in number
- matastatic calcification may be seen in many tissues, including lungs, heart, stomach, and blood vessels
secondary hyperparathyroid
what causes secondary hyperparathyroidism?
any condition that gives rise to chronic hypocalcemia, which in turn leads to compensatory overactivity of the parathyroid glands
what is the most common cause of secondary hyperparathyroidism?
renal failure
- most likely due to decreased phosphate excretion (hyperphosphatemia) -> depresses calcium levels -> stimulating parathyroid gland activity
what is the most common cause of asymptomatic hypercalcemia?
primary hyperparathyroidism
what is caused by a sporadic parathyroid adenoma, or less commonly, parathyroid hyperplasia?
primary hyperparathyroidism
solitary, white hyperplasia that is typically multiglandular
parathyroid adenoma
what are the skeletal manifestations of hyperparathyroidism?
bone resorption, osteitis fibrosis cytsica, and brown tumors
what are the renal changes seen in hyperparathyroidism?
nephrolithiasis and nephrocalcinosis
what are the clinical manifestations of hyperparathyoidism?
painful bones, renal stones, abdominal groans, psychic moans
