Pathologic Calcifications.
Pathologic calcification involves
the abnormal tissue deposition of calcium salts, together with smaller amounts
of iron, magnesium, and other minerals. It is known as dystrophic calcification
when it occurs in dead or dying tissue and as meta- static calcification
when it occurs in normal tissue.
Dystrophic Calcification
Dystrophic calcification represents
the macroscopic deposition of calcium salts in injured tissue. It is often
visible to the naked eye as deposits that range from gritty, sandlike grains to
firm, hard rock material. The pathogenesis of dystrophic calcification involves
the intracellular or extracellular formation of crystalline calcium phosphate.
The components of the calcium deposits are derived from the bodies of dead or
dying cells as well as from the circulation and interstitial fluid.
Dystrophic calcification is
commonly seen in atheromatous lesions of advanced atherosclerosis, areas of
injury in the aorta and large blood vessels, and damaged heart valves. Although
the presence of calcification may only indicate the presence of previous cell
injury, as in healed tuberculosis lesions, it is also a frequent cause of organ
dysfunction. For example, calcification of the aortic valve is a frequent cause
of aortic stenosis in older adults (Fig. 5.4).
Metastatic Calcification
In contrast to dystrophic
calcification, which occurs in injured tissues, metastatic calcification occurs
in normal tissues as the result of increased serum calcium levels
(hypercalcemia). Almost any condition that increases the serum calcium level
can lead to calcification in inappropriate sites such as the lung, renal
tubules, and blood vessels. The major causes of hypercalcemia are
hyperparathyroidism, either primary or secondary to phosphate retention in
renal failure; increased mobilization of calcium from bone as in Paget disease,
cancer with metastatic bone lesions, or immobilization; and vitamin D
intoxication.
