Nephrocalcinosis, the deposition of calcium salts within the renal parenchyma, can be classified by its location; either cortical or medullary.
1. Cortical nephrocalcinosis
Cortical nephrocalcinosis usually occurs as a consequence of chronic glomerulitis, renal cortical necrosis secondary to vascular insult, Alport syndrome, hyperoxaluria, ethylene glycol poisoning, sickle cell disease and rarely, transplant rejection. [1, 2]
2. Medullary nephrocalcinosis
The common causes of medullary nephrocalcinosis include: medullary sponge kidney, renal tubular acidosis, and hyperparathyroidism. Calculi may form in the cavities due to stasis and hypercalciuria, which can also lead to medullary nephrocalcinosis. 
The pattern of parenchymal calcification is described as resembling “railroad tracks” . The calcification at the margins of the renal cortex may be visualised on plain radiographs or on CT. Increased renal cortical echogenicity with preservation of corticomedullary definition can also be seen on ultrasound. However, other medical conditions can mimic this presentation on sonograms, including the interstitial nephritis of AIDS, leukaemia, amyloidosis, subacute renal vein thrombosis, and acute tubular necrosis .
Medullary nephrocalcinosis may be demonstrated on plain radiograph or CT as calcific density in the pyramids. This appearance is indicative of a metabolic abnormality, generally hypercalcaemia or hypercalciuria, but it may also be seen with papillary necrosis and medullary sponge kidney. High pyramidal echogenicity however, may be visualised in the absence of nephrocalcinosis in diseases associated with renal tubular ectasia such as medullary sponge kidney, infantile polycystic kidney disease, and congenital hepatic fibrosis with tubular ectasia. Oxalosis is the only condition that characteristically demonstrates both cortical and medullary calcifications with a diffuse and regular pattern. Although renal oxalosis will produce increased cortical echogenicity early in its course, it will eventually result in echogenic kidneys without adequate differentiation between cortex and medulla .
To conclude, radiology makes it possible to differentiate between the different presentations of nephrocalcinosis. The two patterns of nephrocalcinosis can be visualised on the plain abdominal radiograph, providing a high degree of calcification is present. Computed tomography is a valuable adjunct as minute differences in density can be clearly demonstrated .