Medullary Sponge Kidney

Key Features

• Affects < 1% of the general population

• Present at birth and not usually diagnosed until the third or fourth decade

• Thought to occur due to disruption of the ureteric bud-metanephric mesenchyme interface, often resulting from autosomal dominant mutations in genes responsible for urogenital development; this is associated with medullary cysts that are diffuse, giving a "Swiss cheese" appearance

• Kidneys have a marked irregular enlargement of the medullary and interpapillary collecting ducts and diffuse medullary cysts

Clinical Findings

• Nephrolithiasis affects up to 70% of patients

• Other presentations may include hematuria (either gross or microscopic) or recurrent urinary tract infections

• Common abnormalities include decreased urinary concentrating ability and nephrocalcinosis

• Less common is incomplete type I (distal) renal tubular acidosis

Diagnosis

• CT imaging is preferred, which shows

  • Cystic dilatation of the distal collecting tubules

  • A striated appearance in this area

  • Calcifications in the renal collecting system

Treatment

• Supportive; aimed at underlying abnormalities such as nephrolithiasis and acidosis

• Adequate fluid intake (2 L/day) helps reduce risk of stone formation

• If hypercalciuria is present, thiazide diuretics are recommended because they decrease calcium excretion

• Alkali therapy is recommended if renal tubular acidosis is present