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
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
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.
Echogenic renal pyramids in children
- 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,
- 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.
The prognosis depends mainly on the etiology of the nephrocalcinosis.
The major long-term complication in patients with medullary nephrocalcinosis
is renal failure.
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