Parathyroid gland
General
Anatomy & histology


Topic Completed: 1 January 2013

Minor changes: 31 July 2020

Copyright: 2003-2020, PathologyOutlines.com, Inc.

PubMed Search: (Anatomy[TI] OR histology[TI]) parathyroid[TI]

Monika Roychowdhury, M.D.
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Cite this page: Roychowdhury M. Anatomy & histology. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/parathyroidanatomy.html. Accessed October 20th, 2020.
Definition / general
  • 4 glands in 2 pairs usually close to upper and lower poles of thyroid lobe
  • Discovered in 1880 by Ivar Sandström, a Swedish medical student (Am J Surg Pathol 1996;20:1123)
  • May be found anywhere along pathway of descent of branchial pouches
  • 10% have 2 - 3 glands; 5% have 5 glands, 0.2% have 6 glands
  • Upper pair arises from fourth branchial cleft and descends with thyroid gland; usually at cricothyroid junction
  • Lower pair arises from third branchial cleft and descends with thymus; usually near inferior thyroid
  • Other locations: carotid sheath, anterior mediastinum, intrathyroidal; glands tend to be bilaterally symmetrical
  • Stromal fat increases to 30% at age 25; percent fat is related to constitutional percent fat but reduced in dying individuals; mean is 17% with wide variation (Hum Pathol 1982;13:717)
Drawings

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Embryological pathway of parathyroid migration, showing possible locations for lower parathyroid glands

Parathyroid hormone physiology
  • Release controlled by ionized calcium level with negative feedback system
  • 84 amino acids, derived from cleavage of prepro PTH; biologic activity due to 34 amino acids at amino terminus; other portions are inert but may give false positives in detection systems
  • Binding of PTH to its receptor stimulates cAMP and phosphatidylinositol diphosphate
  • Note: PTH related protein is rarely produced by benign lesions (Am J Clin Pathol 1996;105:487)

Five major actions:
  1. Activates and increases the number of osteoclasts, which mobilizes calcium from bone
  2. Increases renal tubular reabsorption of calcium
  3. Increases conversion of vitamin D to active dihyoxy form in kidneys
  4. Increases urinary phosphate excretion, which reduces calcium loss
  5. Increases GI calcium absorption

Hypercalcemia of malignancy (breast, lung, kidney, myeloma) due to
  1. Release of PTH related protein, usually in advanced disease, or
  2. Osteolytic metastases with local release of cytokines (IL1, TNF alpha)
Gross description
  • Yellow-brown, 25 - 40 mg each gland
Microscopic (histologic) description
  • Composed primarily of chief cells and fat with thin fibrous capsule dividing gland into lobules
  • May have a pseudofollicle pattern resembling thyroid follicles (pink material is PAS positive)

Chief cells:
  • 6 - 8 microns, polygonal, central round nuclei, contain granules of parathyroid hormone (PTH)
  • Basic cell type, other cell types are due to differences in physiologic activity
  • 80% of chief cells have intracellular fat
  • Chief cell is most sensitive to changes in ionized calcium

Oxyphil cells:
  • Slightly larger than chief cell (12 microns), acidophilic cytoplasm due to mitochondria
  • No secretory granules
  • First appear at puberty as single cells, then pairs, then nodules at age 40

Water clear cell:
  • Abundant optically clear cytoplasm and sharply defined cell membranes
  • Chief cells with excessive cytoplasmic glycogen
Microscopic (histologic) images

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Normal parathyroid gland


Chief cells

Oxyphilic nodule

Clear cells

Colloid type material, without oxalate crystals

Positive stains
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