Medullary sponge kidney causes extensive cystic dilation of medullary collecting tubules.1 It is usually an incidental finding in patients undergoing intravenous urography as part of the evaluation for infection, hematuria, or kidney stones.
The classic urographic appearance is linear striations with small brushes or “bouquets of flowers,” which represent the collection of contrast material in small papillary cysts.
Medullary sponge kidney has long been considered a congenital disorder, but the genetic defect has not yet been identified, and the pathogenesis is not yet known. It has only rarely been reported in children.2
It is usually asymptomatic, but complications may occur, including nephrocalcinosis or lithiasis, urinary tract infection, renal tubular acidosis, and impaired urine concentrating ability.
RISK OF LITHIASIS
Gambaro et al3 estimated that medullary sponge kidney is found in up to 20% of patients with urolithiasis, and that more than 70% of patients with medullary sponge kidney develop stones.
Cystic dilation of medullary collecting tubules (an anatomic abnormality) inevitably causes urinary stasis. This, combined with hypercalciuria and reduced excretion of urinary citrate and magnesium (metabolic abnormalities), contributes to lithiasis.4 Lithiasis in medullary sponge kidney is a well-known cause of urinary tract infection, and it tends to facilitate infective stone formation after episodes of urinary tract infection.5
The unique anatomic derangement of medullary sponge kidney contributes to the recurrence of pyelonephritis, in addition to the conventional risk factors—frequent sexual intercourse, avoidance of voiding because it is inconvenient, incomplete bladder emptying, ureteropelvic junction obstruction, ectopic ureter, and impaired immunity.6
DIAGNOSIS AND TREATMENT
Intravenous urography is the gold standard for the diagnosis of medullary sponge kidney; computed tomography and ultrasonography are generally limited in their ability to clearly show the tubular ectasia.7
Treatment includes antibiotics for acute pyelonephritis and thiazide diuretics and potassium citrate to prevent stone formation and renal tubular acidosis. Due to its silent course, medullary sponge kidney should be considered not only as a cause of nephrocalcinosis and nephrolithiasis, but also as a distinct entity complicating recurrent pyelonephritis.