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Retroperitoneum » Kidneys, Ureters
Medullary sponge kidney
Author(s): Chaitali Shah, FRCR | Ashok Bhanushali, MD
ArticleOther contents by this Author
 
 
Introduction

The term nephrocalcinosis refers to radiologically demonstrable diffuse renal parenchymal calcifications.

Etiology

Although medullary nephrocalcinosis is characteristic of medullary sponge kidney, 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.

Pathogenesis

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, calculus disease, hematuria or repeated urinary tract infections.

Ultrasound features

Ultrasound features in patients with MSK: these are quite non-specific and 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 or may not cast any posterior shadowing.


Caption : Sagittal image 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.

Please click here to view the source of this image.


Caption : Sagittal image of the left kidney

Description : The right kidney is normal in size, but exhibits increased echogenicity of the medullary pyramids. No obvious acoustic shadowing is noted from the echogenic foci.



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.


Other modalities

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.

References

1. Patriquin HB, O`Regan S. Medullary sponge kidney in childhood. AJR Am J Roentgenol. 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 Am J Roentgenol. 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 Am J Roentgenol. 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.