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Retroperitoneum » Kidneys, Ureters
Medullary nephrocalcinosis due to medullary sponge kidney
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Presentation An adult woman presented with two episodes of painless hematuria. Her renal function tests, serum calcium and parathormone levels were normal.
 
 
 
Caption: Sagittal scan of the left kidney.
Description: The left kidney is also normal in size and demonstrates extensive, curvilinear parenchymal calcification with posterior shadowing in the region of the medulla.
 
 
 
Caption: Sagittal scan of the right kidney.
Description: The kidney is normal in size but shows extensive echogenic foci in the region of the medulla. Some of these foci show posterior acoustic shadowing.
 
Differential Diagnosis Medullary nephrocalcinosis [which has many causes including medullary sponge kidney, renal tubular acidosis, sarcoidosis, metastatic disease, hyperparathyroidism and milk alkali syndrome].

 
Final Diagnosis Bilateral medullary nephrocalcinosis, most likely due to medullary sponge kidney.
 
Discussion

The term nephrocalcinosis refers to radiologically demonstrable diffuse renal parenchymal calcifications. Although medullary nephrocalcinosis is characteristic of medullary sponge kidney [MSK], a diverse group of diseases can produce this appearance including those that cause systemic metabolic alterations of hypercalcemia and hypercalciuria. Some of the common conditions associated with medullary nephrocalcinosis are medullary sponge kidney, hyperparathyroidism, renal tubular acidosis, sarcoidosis and metastatic disease.

Medullary sponge kidney is a developmental anomaly characterized by cystic dilatation of the collecting tubules in one or more renal medullary pyramids. It is of uncertain etiology and almost always diagnosed radiologically. This disease may be asymptomatic or may be characterized by repeated renal colics, calculous disease, hematuria or repeated urinary tract infections.

Ultrasound features in patients with MSK, which are quite non-specific, include-
•Predominantly bilateral involvement, but may be unilateral or segmental [focal].
•Normal sized kidneys if no associated complications.
•Echogenic medullary pyramids, irrespective of medullary nephrocalcinosis. Some of these may cast posterior acoustic shadowing as illustrated in this case, or may not cast any posterior shadowing [click here to view].

Ultrasound may also detect associated complications such as-
•Calculi- seen as dense, echogenic foci casting a shadow.
•Obstructive nephropathy- enlarged kidneys, hydronephrosis.
•If repeated UTI, patients may develop pyelonephritis [not detected well on ultrasound] and renal abscess. An abscess is seen on ultrasound as a focal hypoechoic mass that may be solid or liquefying. These findings are better delineated by CT or MR.

Role of ultrasound in MSK-
•Establish a diagnosis.
•Monitor adult patients to detect complications.
•In children with MSK, an association is noted with Wilm’s tumors and other abdominal tumors; hence, periodic surveillance is performed with ultrasound.

Excretory urograms in MSK have a classic radiological appearance. Pools of contrast media collection in the ectatic ducts give it the appearance of ‘bouquet of flowers’ or ‘bunch of grapes’ and this is the diagnostic sign. CT scan is very sensitive in the detection of papillary calcifications and complications occurring in MSK, however no characteristic finding of MSK has been described.

 
Case References 1. Patriquin HB, O`Regan S. Medullary sponge kidney in childhood. AJR. 1985 Aug; 145(2):315-9.
2. Kuiper JJ. Medullary sponge kidney. Perspect Nephrol Hypertens. 1976;4:151-71.
3. Ginalski JM, et al. Does medullary sponge kidney cause nephrolithiasis? AJR. 1990 Aug; 155(2):299-302.
4. Prat V, Drab K, et al. Clinical picture of 11 patients with sponge kidney. Cas Lek Cesk. 1991 Mar 1; 130(9):276-7.
5. Riehl J, Schneider B, et al. Medullary nephrocalcinosis: sonographic findings in adult patients. Bildgebung. 1995 Mar; 62(1):18-22.
6. Glazer GM, Callen PW, et al. Medullary nephrocalcinosis: sonographic evaluation. AJR. 1982 Jan; 138(1):55-7.
7. Ginalski JM, et al. Medullary sponge kidney on axial computed tomography: comparison with excretory urography. Eur J Radiol. 1991 Mar-Apr;12(2):104-7.
 
Follow Up This patient had no other complaints other than the two episodes of hematuria. Her renal function tests, serum calcium and parathormone levels were normal. This patient underwent a CT scan which confirmed the presence of medullary calcinosis and showed no additional findings. She was placed on regular ultrasound surveillance and is currently doing well.
 
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