Ultrasonography of both kidneys in 9 year old female showing multiple areas of increased echogenicity involving all of the medullary pyramids consistent with nephrocalcinosis. The renal cortex is normal in echogenicity. There is no evidence of hydronephrosis.
Medullary nephrocalcinosis refers to calcification in the medullary pyramids rather than the renal collecting system. It is caused by a number of processes, but the three most common are : hyper-parathyroidism medullary , renal tubular acidosis and sponge kidney (tubular ectasia). Medullary nephrocalcinosis is usually associated with hypercalcuria and often with hypercalcemia. Primary hyperparathyroidism and distal renal tubular acidosis account for over 60% of these cases. The remaining 40% of cases are due to a variety of other causes of hypercalciuria, including milk-alkali syndrome, Cushing's syndrome, bony metastases, hyperthyroidism, hypothyroidism, sarcoidosis, furosemide therapy, and in this case, vitamin D therapy.
Ultrasonography is more sensitive than conventional radiography and CT and sonography is unusually sensitive in detecting this condition, and the sonographic changes predate any visible calcification and are generally more dramatic than the abnormalitie seen on CT. Nephrocalcinosis may affect some or ail of the pyramids. The deposits of calcium phosphate and calcium oxalate in the interstitium of the renal pyramids reverse the sonographic appearance of the normal kidneys. The pyramids are normally hypoechoic relative to the cortex. In its early stages it causes increased medullary echogenicity at the periphery of the pyramids and eventually involves the entire pyramids. With progressive calcification, shadowing begins. A regular arrangement of hyperechoic pyramids are seen which may shadow if large calcified foci are present, but not if the foci are numerous and tiny, as they are smaller than the beam width. Less frequently, calcification is seen in the renal cortex.