22-28: Medullary Sponge Kidney

Medullary sponge kidney is a disease involving the distal nephron that affects less than 1% of the general population. Although present at birth, it is not usually diagnosed until the third or fourth 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 marked, irregular enlargement of the medullary and papillary collecting ducts. This is associated with diffuse medullary cysts, giving a “Swiss cheese” appearance in these regions.

CLINICAL FINDINGS

Nephrolithiasis is the most common clinical presentation of medullary sponge kidney, affecting up to 70% of patients. Other presentations may include hematuria (either gross or microscopic) or recurrent UTIs. Common abnormalities include decreased urinary concentrating ability, nephrocalcinosis, and, less commonly, type 1 (distal) renal tubular acidosis. The diagnosis is established clinically through laboratory data and imaging characteristics. CT imaging is the preferred imaging study, which 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

Medullary sponge kidney is generally considered a benign condition unless there are complications from recurrent UTIs, nephrolithiasis, or uncontrolled acidosis.