SM158 Parathyroid Histology/Pathology Flashcards
Normal number of parathyroid glands, arrangement, color, anatomical location
4 glands normally (can have 5 or 6)
Arranged in 2 pairs (upper and lower)
Color varies from red to tan to yellow depending on fat content
Upper pair: posteriolateral border of the middle third of thyroid, lower pair: posteriolateral border of the lower third
Embryology of upper and lower pairs of glands
Upper: arises from 4th branchial cleft, descends with the thyroid gland
Lower: arises from the 3rd branchial cleft, descends with the thymus
Chief cell histology
Main cell type. Pink, polygonal, central/round/uniform nuclei, water-clear appearance when glycogen is abundant. Secretory granules with PTH.
Oxyphil cell histology
Slightly larger than chief cells, acidic cytoplasm, packed with mitochondria. Glycogen granules present but no secretory granules.
What stimulates release of PTH?
Level of free calcium in the blood (hypocalcemia = more release)
5 ways that PTH regulates serum calcium levels
1) Increases renal tubular absorption
2) Converts vit. D to active form in kidneys
3) Increases urinary phosphate excretion
4) Increases gut absorption
5) Mobilizes stores from bone
Anomalous sites where the parathyroid glands might end up
Carotid sheath, behind the cervical or thoracic esophagus, mediastinum, inside the thyroid, pharynx
Most common cause of clinically apparent hypercalcemia
Malignancy
Pathophys of hypercalcemia in malignancy
Consequence of bone resorption (either from metastases or PTHrP). With PTHrP, expression of RANKL on osteoblasts is promoted. These osteoblasts bind RANK on osteoclast progenitors, inducing their differentiation into mature osteoclasts.
3 most common causes of primary hyperparathyroidism
Adenoma > hyperplasia > carcinoma
Genetic syndrome associated with primary hyperparathyroidism
MEN-1
MEN-2A
Familial hypocalcuric hypercalcemia (CASR gene)
Parathyroid adenomas: gross and microscopic appearance
Gross: well-circumscribed, soft, tan or red nodule with a delicate capsule. Other glands will be normal in size or shrunken (due to feedback inhibition)
Microscopic: uniform polygonal chief cells with small nuclei. Adipocytes are usually absent
How do you differentiate parathyroid adenoma and primary hyperplasia?
Typically, adenomas are singular and the other glands will be normal-sized or shrunken. In hyperplasia they should all be enlarged.
Parathyroid carcinoma: gross and microscopic appearance
Gross: it can look like an adenoma or it can clearly have infiltrated surrounding tissue (poorly-circumscribed). Grey-white, more irregular.
Microscopic: looks like normal chief cells. Surrounded by a dense, fibrous capsule. Only reliable criteria is metastasis.
What type of bone is most affected by hyperparathyroidism?
Cortical > cancellous
Generalized osteitis fibrosa cystica triad
A.K.A. von Recklinghausen disease
1) increased bone cell activity (both -clasts and -blasts), 2) peritrabecular fibrosis, 3) cystic brown tumors
Brown tumor pathogenesis
Bone loss causes microfractures and secondary hemorrhages, which leads to an influx of macrophages and ingrowth of reparative fibrous tissue
Other condition in DDx for brown tumor hyperparathyroidism?
Central giant cell granuloma of bone
Indistinguishable from brown tumor, also affects jaw
Differentiate because no elevated PTH or hypercalcemia
Examples of morphological changes in the bone of individuals with secondary hyperparathyroidism
Dissecting osteitis (“railroad tracks”)
Subperiosteal resorption
Brown tumors
Osteoporosis
Hyperparathyroidism symptoms
Mnemonic: painful bones, renal stones (nephrolithiaisis), abdominal groans, and psychic moans (depression, lethargy)
Secondary hyperparathyroidism: most common etiology, pathology, symptoms
Chronic renal failure is most common cause
Path: more chief cells, more water-clear cells, less fat cells
Symptoms: dominated by renal failure
Tertiary hyperparathyroidism
Parathyroid activity becomes autonomous and excessive, causing hypercalcemia
Hypoparathyroidism: main etiology
Inadvertent consequence of surgery (thyroidectomy usually)
