A 36-year-old female presented with the chief complaint of on and off flank pain for the last 6 months. It was not associated with fever or burning micturition. No discolouration of urine was noted. There was no history of diabetes or hypertension. No significant previous medical history was noted.
Diagrammatic representation of cross section of kidney demonstrates the classic locations of the medullary and cortical nephrocalcinosis (Fig 1). Different patterns of cortical calcification are also demonstrated (Fig 1). Pictorial illustration of nephron demonstrates the concentrating mechanism of kidney with differentiation of different parts in renal cortex and medulla (Fig 2). CT urography, in our case, showed diffuse calcification in bilateral medullary pyramids (Fig 3). The calcification was bilaterally symmetrical and involved the medulla in upper, mid and the lower poles evenly (Fig 4). Approximately 9.1mm x 7.0mm sized calculus was noted in the lower pole calyx of the left kidney (Fig 5). The calculus measured homogeneous attenuation of approximately +1286 HU. No calculus was noted in bilateral ureters or in the urinary bladder. No dilatation of the pelvicalyceal system or of the ureters was noted. Normal excretion of contrast was noted from bilateral kidneys (Fig 5).
Calcification within the kidney can occur either in the renal parenchyma (nephrocalcinosis) or in the collecting system (nephrolithiasis) . Renal parenchymal calcification is further classified as either medullary nephrocalcinosis or cortical nephrocalcinosis. Because of the concentrating effects of the loops of Henle which lie in the renal medulla, renal medullary calcification is far more common than the cortical calcification . Common causes of renal cortical nephrocalcinosis are chronic glomerulonephritis, acute cortical necrosis and oxalosis. Similarly, major causes of medullary calcification are renal tubular acidosis, medullary sponge kidney and hyperparathyroidism . These parenchymal calcific deposits can rupture through the papillary epithelium into the calyceal system to become urinary stones. Therefore it is common for the patients with nephrocalcinosis to present with symptoms of renal colic and haematuria.
Cortical and medullary calcifications are evident on abdominal x-rays, ultrasonographic studies and CT scans. Ultrasonogram is the preferred modality of choice for the evaluation of mild to moderate nephrocalcinosis . However, in severe cases of nephrocalcinosis with repeated calculi formation and concern about the urinary tract as well, CT urography needs to be undertaken. The main concern with CT urography is the radiation dose that can best be avoided in mild to moderate cases by using the ulternative modality of images, i.e, ultrasonography. On abdominal X-rays, cortical nephrocalcinosis may appear as thin peripheral band of calcification, tram lines or diffuse punctate calcifications. On ultrasonographic study, renal cortex is diffusely echogenic with corresponding areas of cortex showing high attenuation in the CT. Medullary calcification on the other hand is central in location and spares the cortex. It is usually bilateral with stippled calcification in the medullary pyramids. Ultrasonographic study shows diffusely echogenic renal medulla without posterior shadowing . CT scan shows calcific deposits along the renal medulla that are usually bilateral and symmetrical. Contrast-enhanced nephrographic phase gives high-resolution images of the kidneys that can detect medullary cysts as well (an advantage over the ultrasonographic study) . Nephrolithiasis is a common complication of nephrocalcinosis and should always be looked for. They can be in the pelviclyceal system, in the ureter or in the urinary bladder. Associated hydronephrotic changes might also be present.
Treatment of nephrocalcinosis depends upon the underlying cause. Proper hydration of the body is the basic management in all the cases. Dietary modification to reduce hypercalciuria and use of citrates have also been found to be helpful. Prognosis of nephrocalcinosis depends upon the underlying cause with only few patients, without treatment, progressing to end stage renal disease .
Take Home Message: Medullary nephrocalcinosis is a form of intrarenal calcification that occurs in the medulla and commonly involves bilateral kidneys. Patients with medullary nephrocalcinosis can develop nephrolithiasis leading to repeated episodes of renal colic. Treatment of the underlying cause can prevent recurrent renal calculus formation and hence reduce the morbidity associated with the disease.
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