22-28: Medullary Sponge Kidney

Medullary sponge kidney is believed to affect less than 1% of the general population. Although present at birth, it is not usually diagnosed until the fourth or fifth decade. It is 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. Kidneys have a marked irregular enlargement of the medullary and interpapillary collecting ducts. This is associated with medullary cysts that are diffuse, giving a “Swiss cheese” appearance in these regions.

CLINICAL FINDINGS

Nephrolithiasis is the most common clinical presentation for medullary sponge kidney. Other presentations may include hematuria (either gross or microscopic) or recurrent urinary tract infections. Common abnormalities are a decreased urinary concentrating ability and nephrocalcinosis; less common is incomplete type 1 distal renal tubular acidosis. The diagnosis is established clinically through laboratory data and imaging characteristics. As the preferred imaging test, CT shows cystic dilatation of the distal collecting tubules with a striated appearance, and calcifications in the renal collecting system. Similar findings on ultrasound may also support the diagnosis.

TREATMENT

Treatment for medullary sponge kidney is supportive and 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.

PROGNOSIS

Renal function is well maintained unless there are complications from recurrent urinary tract infections and nephrolithiasis.