IS Case 93: Medullary Nephrocalcinosis
Imaging Sciences URMC 2008
Publication Date: 2009-05-20
Nephrocalcinosis describes deposition of calcium into the renal parenchyma with medullary deposition most common (95%). On US the earliest sign is absence of hypoechoic papillary structures. Next a hyperechoic rim forms at the corticomedullary junction and then finally generalized increased echogenicity of the renal pyramids with or without shadowing. There is an extensive differential diagnosis with distal renal tubular acidosis (type 1) most common when there is uniform medullary deposition of calcium. Other more common etiologies include skeletal deossification seen in conditions such as hyperparathyroidism, bone metastases, and prolonged immobilization. When there is asymmetric deposition of calcium it is most commonly secondary to stones that develop within papillary tips in dilated collecting ducts. This occurs in medullary sponge kidney.
Cortical nephrocalcinosis (5%) is less common and is most often related to chronic glomerulonephritis or acute cortical necrosis. However, this carries a higher risk for development of renal failure. This may be seen in transplanted kidneys undergoing chronic rejection. On US the kidney is more echogenic than the liver. Cortical nephrocalcinosis presents as a thin rim of calcification outlining the cortex or may have a spotty appearance.
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