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Abdomen » Kidneys/Ureters
Medullary nephrocalcinosis secondary to prolonged immobilization
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Presentation A 9 year old boy presents with urinary tract infection. There is a past medical history of a femoral fracture 6 months ago and a body cast for 7 weeks.
Caption: Sagittal view of right kidney
Description: There are increased triangular shaped echogenicities noted in the right kidney. This is in the distribution of the renal pyramids. There is no associated acoustic shadowing.
Caption: Transverse view of right kidney
Description: The increased echogenicity in the region of the renal pyramids is noted again.
Differential Diagnosis Medullary nephrocalcinosis
Final Diagnosis Medullary nephrocalcinosis secondary to prolonged immobilization

Medullary nephrocalcinosis is the result of calcification in the medullary portions of the kidney in the distribution of the renal pyramids. This condition varies from a subtle distribution of the calcifications to a florid deposition of calcium throughout the pyramids. With minimal calcifications, there is no shadowing. Ultrasound is more sensitive than x-ray or CT in detecting the faint calcifications.

Ultrasound features of medullary nephrocalcinosis:
1. Early- hyperechogenicity in the periphery of the pyramids
2. Mid- diffusely hyperechoic pyramids, fine to coarse echotexture
3. Late: clumps of calcium, shadowing

The causes of medullary nephrocalcinosis are many, but the common thread is a high calcium state.  Medullary sponge kidney is different in that it is a congenital abnormality (due to tubular ectasia or dilated collecting tubules).

See http://www.sonoworld.com/Client/Cases/CaseDetails.aspx?CaseId=85 for an example and discussion of medullary sponge kidney.  

See http://www.sonoworld.com/Client/Cases/CaseDetails.aspx?CaseId=112 for an example of nephrocalcinosis in the adult.

See http://www.sonoworld.com/Client/Cases/CaseDetails.aspx?CaseId=111 for a case of cortical nephrocalcinosis due to renal tubular acidosis.

External links:

Goldminer: http://goldminer.arrs.org/search.php?query=medullary%20nephrocalcinosis

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