Nephrocalcinosis

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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.

Ultrasound :
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.

Differential :
Echogenic renal pyramids in children
* Nephrocalcinosis
- latrogenic : furosemid, vitamin D.
- Non-iatrogenic : idiopathic hypercalcaemia, Williams' syndrome, Kenny-Caffey syndrome, absorptive hypercalcaemia, renal tubular necrosis, tubular necrosis or dystrophic calcification, chronic glomerulonephritis, malignancy, Sjogrens syndrome.
* No nephrocalcinosis
- Protein deposits proteinuria (shock, dehydration), toxic shock syndrome, sepsis, degenerative leucoencephalopathy, hypotensive or hypovolaemic shock.
- Vascular congestion or occlusion : sickle cell disease.
- Systemic infection : bacterial septicaemia, Candida, cytomegalovirus, AIDS.
- Metabolic causes : Gout-Lesch-Nyhan syndrome, glycogen storage disease, hypokalaemia primary aldosteronism, pseudo-Bartter syndrome, Wilson syndrome, Fanconi's syndrome, tyrosinosis, cholestatic jaundice, oxalosis, alpha antitrypsin deficiency.
- Fibrosis : renal pyramidal fibrosis ( usually forms a part of a generalised parenchymal abnormality), congenital hepatic fibrosis.
- Others causes : cystic medullary disease, medullary sponge kidney, metabolic alkalosis, tubular ectasia (infantile and juvenile polycystic kidneys), intrarenal reflux, pyloric stenosis, Crohn's disease.

Prognosis:
The prognosis depends mainly on the etiology of the nephrocalcinosis.
The major long-term complication in patients with medullary nephrocalcinosis is renal failure.

Reference :
* 1 Auron A, Alon US. Resolution of medullary nephrocalcinosis in children with metabolic bone disorders. Pediatr Nephrol. 2005 Aug;20(8):1143-5. Epub 2005 Jun 23.
* 2 Zajadacz B, Juszkiewicz A. Nephrocalcinosis in a 2-month-old girl suffering from a mild variant of idiopathic infantile hypercalcemia. Wiad Lek. 2004;57(11-12):710-2.
* 3 Sakamoto H, Tomizawa T, Tamura T, Fujita K, Sato K, Tamura J. Bilateral nephrocalcinosis associated with distal renal tubular acidosis. Intern Med. 2005 Jan;44(1):81-2.
* 4 Hein G, Richter D, Manz F, Weitzel D, Kalhoff H. Development of nephrocalcinosis in very low birth weight infants. Pediatr Nephrol. 2004 Jun;19(6):616-20. Epub 2004 Mar 31.
* 5 Laube GF, Leonard JV, van't Hoff WG. Nephrocalcinosis and medullary cysts in 3-methylglutaconic aciduria. Pediatr Nephrol. 2003 Jul;18(7):712-3. Epub 2003 May 15
* 6 Kim YG, Kim B, Kim MK, Chung SJ, Han HJ, Ryu JA, Lee YH, Lee KB, Lee JY, Huh W, Oh HY. Medullary nephrocalcinosis associated with long-term furosemide abuse in adults. Nephrol Dial Transplant. 2001 Dec;16(12):2303-9
* 7 Moudgil A, Rodich G, Jordan SC, Kamil ES. Nephrocalcinosis and renal cysts associated with apparent mineralocorticoid excess syndrome. Pediatr Nephrol. 2000 Nov;15(1-2):60-2
* 8 Schell-Feith EA, Kist-van Holthe JE, Conneman N, van Zwieten PH, Holscher HC, Zonderland HM, Brand R, van der Heijden BJ. Etiology of nephrocalcinosis in preterm neonates: association of nutritional intake and urinary parameters. Kidney Int. 2000 Nov;58(5):2102-10.
* 9 Campfield T, Bednarek FJ, Pappagallo M, Hampf F, Ziewacz J, Wellman J, Rockwell G, Braden G, Flynn-Valone P, Neylan M, Pangan A. Nephrocalcinosis in premature infants: variability in ultrasound detection. J Perinatol. 1999 Oct-Nov;19(7):498-500.
* 10 Mourani C, Khallouf E, Akkari V, Akatcherian C, Cochat P. [Early hypomagnesemia, hypercalciuria and nephrocalcinosis: two cases in a family] Arch Pediatr. 1999 Jul;6(7):748-51.
* 11 Pfitzer A, Nelle M, Rohrschneider W, Linderkamp O, Troger J. [Incidence of typical nephrocalcinosis ultrasound findings in premature infants during enteral calcium and phosphate administration] Z Geburtshilfe Neonatol. 1998 Jul-Aug;202(4):159-63.
* 12 Alon US. Nephrocalcinosis. Curr Opin Pediatr. 1997 Apr;9(2):160-5. Review.
* 13 Riehl J, Schneider B, Bongartz D, Sieberth HG. Medullary nephrocalcinosis: sonographic findings in adult patients. Bildgebung. 1995 Mar;62(1):18-22