Practical Aspects of Calcification and Ossification in the Various Body Tissues

THE recent unfolding of many new facts concerning the mechanisms of calcification, with the concomitant descriptions of new syndromes such as hyperparathyroidism and hypervitaminosis, makes the consideration of the entity, “Calcification and Ossification in the Various Body Tissues,” a subject of signal interest to the roentgenologist (1, 2, 3). It is not generally appreciated that there are numerous factors governing calcification, and almost as many theories of the mechanism involved have been propounded. Factors Concerned in Calcification The following brief discussion of the most important factors is of special importance in understanding pathologic calcification in the various tissues (4). (A) Blood Plasma Calcium.—A large part of the calcium in the diet must be brought into solution before absorption. This is dependent upon several factors. The soluble salts are thrown out of solution by (a) the alkaline carbonates in the digestive juices; (b) by fatty acids. The dependence of calcium metabolism upon a normal fat metabolism explains the abnormally low blood calcium values and also the poor absorption of vitamin D, resulting in the bone changes we see in the so-called celiac rickets. Again, acidity of the intestinal contents favors the increased absorption of calcium, otherwise excess phosphorus must be balanced with that of calcium, or excess phosphorus combines with calcium as the insoluble calcium phosphate and causes calcium deprivation. If calcium is in excess, a certain amount forms the insoluble phosphate and a considerable amount is excreted as other salts. The excretion of calcium occurs through the kidney and large bowel. So we see the formation of calculi due to excessive excretion of calcium, through the kidney, from over-absorption due, in turn, to acid bowel content. Again, renal calculi are observed in certain bedridden patients, in cases in which decalcification often is due to inactivity, leading to the abnormal excretion of calcium, with deposition. The calculi may disappear when the patient resumes active life. (B) Vitamin D.—Vitamin D is essential to normal calcium and phosphorus metabolism. It is indispensable for maintaining the normal calcium and phosphorus concentration and ratio in the blood and for the normal formation of bone. There is an increased net retention of calcium and phosphorus brought about through the resultant of two opposing factors: (1) The increased absorption from the diminished excretion into the intestines; (2) the increased elimination by the kidneys (5,6,7). Hypervitaminosis D can cause widespread calcification in the arteries and possibly in other tissues (8). In children, we have seen hypervitaminosis D cause an unusually dense zone of calcification in the metaphyses of the long bones. (C) Parathormone.—The physiological effects of the parathyroid hormone have been briefly outlined by Aub (9): (1) To raise the blood calcium and lower the blood phosphorus. (2) Possibly to increase the ionized calcium in the blood. (3) To increase the calcium and phosphorus excretion in the urine.