Mineralisation - Pathology

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  • Calcification is the deposition of calcium in tissues other than bone and teeth.
  • Where sufficient amounts are deposited to be seen grossly, it imparts a whitish colour to the area.
  • There are two types of calcification:
    1. Dystrophic
    2. Metastatic (Hypercalcaemia)


  • Occurs in damaged tissue.
    • Dead tissue is alkaline - favours the deposition of calcium.
  • Deposition is usually irreversible.
  • NOT related to elevated levels of calcium in the blood.
  • Commonly seen in:
    • Caseous necrosis in tuberculous granulomas.
    • Dead migrating parasites in various tissues
    • In part of Vit.E/selenium deficiency in livestock
      • Calcium is deposited in the necrotic tissue.
Gross Appearance
  • Calcium salts have dull grey white chalky and granular appearance in tissue.
  • Granules are hard.
    • Feel gritty if cut or palpated.
Histological Appearance
  • Stains as irregular blue-purple clumps (sometimes shattered) with H&E.
    • Can be confused with bacteria.
  • Von Kossa is a special stain that colours calcium black.

Metastatic (Hypercalcaemia)

  • Metastatic calcification is calcification of normal tissue without previous damage.
  • Is a result of hypercalcaemia.
  • Calcium salts are laid down on basement membranes and elastic fibres, for example
    • Blood vessel walls
    • Pleura
    • Mucous membranes of the lungs, kidneys, and stomach.
    • Endocardium
    • Tendons and ligaments of joints.
  • Causes of hypercalcaemia
    1. Primary Hyperparathyroidism
      • A rare condition
      • An adenoma of the parathyroid gland produces parathyroid hormone.
        • Stimulates osteoclasts to resorb calcium from bone, producing hypercalcaemia.
    2. Secondary Hyperparathyroidism
      • Renal hyperthyroidism
        • Occurs in chronic kidney failure.
        • Kidneys retain phosphate.
          • Disturbs the calcium:phosphate ratio.
            • Stimulates the parathyroid gland to resorb calcium from bone.
        • Calcium resorption from bone is compounded by lack of activated Vit. D.
          • This is due to the kidney damage.
      • Nutritional hyperthyroidism
        • The parathyroid stimulation here is due to excessive phosphates in the diet
          • E.g. a grain diet.
          • Upsets the calcium:phosphate ratio.
      • Hypervitaminosis D
        • Due to
          • Therapy
          • Ingestion of some plants which produce substances mimicking Vit. D .
        • Results in increased calcium absorption from the gut, and hence hypercalcaemia.
      • Tumours which produce hormone like activity
        • E. g.
          • Some lymphosarcomas
          • Anal gland apocrine malignant tumour
          • Some carcinomas

Other Conditions in Which Calcium is Deposited

Calcinosis circumscripta
  • A condition of dogs
    • Particularly affects young German Shepherd Dogs.
  • Nodules of a pasty calcium material are laid down in the dermis.
    • Especially laid down near bony prominences.
  • Aetiology is unknown,
    • May be related to damage of sweat glands.
      • These are often in the vicinity of the deposits.
Calcinosis cutis
  • In Cushing’s Disease (hyperadrenocortism).
  • Calcium is diffusely deposited on the collagen and elastin of the dermis .


  • A metaplastic change in soft tissues.

Extracellular crystals

Ethylene Glycol Poisoning

  • Accidental ethylene glycol (antifreeze) poisoning is not uncommon in small animals.
  • Ethylene glycol is metabolised in the liver to oxalate.
    • Oxalate crystals precipitates in the renal tubules.
      • Can cause severe traumatic damage.


  • Gout occurs with excessive retention of uric acid/urates and their deposition in tissue.
  • Fairly common in man.
    • The crystals are deposited in joint tissue, particularly those of the toe.
      • Sometimes occurs in the tarsal joints of birds.
  • In birds, other tissues are more commonly affected.
    • The serous membranes of the body cavities.
      • Look like they have been dipped in flour.
    • The substance of the kidney
      • The star-shaped crystals may block the tubular lumen.
        • Their sharp edges may also damage the tubular epithelium and underlying basement membrane.
          • Provokes a host cellular response.
  • The exact pathogenesis in birds is unknown.
    • Birds excrete semisolid urates through the kidneys.
      • This may predispose them to blockages.
    • Other suggested predispositions include
      • Vitamin A deficiency
      • Prior kidney damage due to an inflammatory process
      • Abnormal protein metabolism
  • Tortoises are also susceptible to gout.