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Medullary
sponge kidney is formation of diffuse, bilateral medullary
cysts caused by abnormalities in pericalyceal terminal collecting
ducts.
The cause of medullary sponge kidney is unknown, but genetic transmission occurs in < 5% of cases. The disorder is more common among patients with Ehlers-Danlos, Marfan, or Beckwith-Wiedemann syndromes; congenital hemihypertrophy; or congenital dilation of intrahepatic bile ducts (Caroli's disease).
Most patients are asymptomatic, and the disorder usually remains undiagnosed. It predisposes to calculus formation and UTI, so the most common presenting symptoms are renal colic, hematuria, and dysuria. Urinalysis typically shows evidence of incomplete distal renal tubular acidosis (overt metabolic acidosis is rare) and decreased urine-concentrating ability without symptomatic polyuria.
Diagnosis is generally by CT, but IVU can be used. Ultrasonography is not helpful because cysts are small and located deep in the medulla. Differential diagnosis includes renal cystic dysplasia, papillary necrosis, pyelonephritic cysts, TB, and other conditions that cause nephrocalcinosis.
Medullary sponge kidney is benign, and long-term prognosis is excellent. Obstruction by renal calculi may transiently reduce GFR and increase serum creatinine. Treatment is indicated only for UTIs and for recurrent calculus formation. Thiazides (eg, hydrochlorothiazide 25 mg bid) and high fluid intake inhibit calculus formation and may reduce incidence of obstructive complications.
Last full review/revision November 2005
Content last modified November 2005
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