Nephrocalcinosis: by default, we apply this term to ‘medullary’ calcification (= medullary nephrocalcinosis), though it can occur in renal cortex (e.g. in renal cortical necrosis of pregnancy or chronic active glomerulonephritis). Nephrocalcinosis is associated with conditions that cause hypercalcemia, hyperphosphatemia, and increased excretion of calcium, phosphate, and/or oxalate in the urine. Hypocitraturia also may contribute, especially in those with distal (type 1) renal tubular acidosis. Citrate normally inhibits crystal formation by forming a complex with calcium.
Important conditions that cause Medullary nephrocalcinosis: With hypercalcemia + hypercalciuria: primary hyperparathyroidism, sarcoidosis, too much vitamin D. Conditions with hypercalciuria but no hypercalcemia: Distal renal tubular acidosis, medullary sponge kidney, too much furosemide.
On a renal sonogram, the medullary pyramids appear bright or white (hyperechoic) instead of anechoic or hypoechoic. Kidney appears like a stretched chrysanthemum flower. Acoustic shadowing may or may not be seen. Sometimes, the whole pyramid becomes hyperechoic while sometimes it’s only the rim (especially in early stages). In mild cases, ultrasound might actually be more sensitive than CT scan in detecting this finding.
Following are images obtained from a patient on high-dose calcium/vitamin D supplementation demonstrating this finding (? hypercalciuria).