How is medullary sponge kidney (MSK) diagnosed during the workup for nephrolithiasis?

Updated: Jun 21, 2018
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Answer

Medullary sponge kidney (MSK), also called tubular or ductal ectasia or cystic dilation of the collecting ducts, is a generally benign congenital condition that demonstrates dilation of the distal renal collecting tubules on IVP as the tubules fill with contrast. These normally invisible microscopic tubules show a whitish blush in the papilla in persons with MSK. In severe cases, stones, cysts, and diverticula can be present. The condition can be unilateral, or even limited to one calyceal system, but it is bilateral in 70% of patients. It is not usually discovered until the second or third decade of life, even though MSK is congenital.

MSK is the most common anatomical problem found in calcium nephrolithiasis patients, affecting approximately 2% overall. Most stones in patients who have MSK are composed of calcium oxalate with or without calcium phosphate. Stones tend to be small and are usually passed spontaneously.

In most cases, MSK is not hereditary, although rare autosomal inherited forms have been described. The exact cause is unknown, but it could be caused by tubular obstruction due to calcium oxalate calculi from infantile hypercalciuria or collecting duct dilation from blockage by fetal uric acid stones, embryonal remnants, or other material.

The most accurate way to demonstrate MSK is to employ high-quality excretory urography (ie, IVP) with serial renal tomography starting just before the injection of the contrast media and continuing every 4 minutes for the next 20 minutes.

Most patients with MSK are asymptomatic; unless they have an IVP for an unrelated reason, the condition may never be diagnosed. Of patients who are symptomatic, renal colic and calcium urinary stones are the most common problems. (UTIs and hematuria are the others.) Women are more likely to have MSK than men.

Some patients with MSK may report severe chronic renal pain without any evidence of infection, stones, or obstruction. The etiology of this pain is unclear. These patients may be treated best by physicians comfortable with the management of chronic pain disorders, although recent reports suggest that ureteroscopic laser papillotomy may provide temporary relief. [31]

Long-term management of MSK, as in any frequent stone former, is aimed toward identifying metabolic risk factors for continuing stone formation, with serum and 24-hour urine testing. The most common metabolic problems in MSK are hypercalciuria and hypocitraturia.


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