Medullary Sponge Kidney
In medullary sponge kidney, the collecting ducts in the renal pyramids dilate, and cavities, clefts, and cysts form in the medulla. This disorder may affect only a single pyramid in one kidney or all pyramids in both kidneys. Although an affected kidney may be of normal size, it’s usually somewhat enlarged and spongy.
Because this disorder typically is asymptomatic and benign, it’s commonly overlooked until the patient reaches adulthood. Although found in both sexes and in all age groups, it’s usually diagnosed in adolescents and in adults ages 30 to 50. The prognosis is good.
Medullary sponge kidney is unrelated to medullary cystic disease, a hereditary disorder. The conditions are similar only in the presence and location of the cysts.
Causes
Medullary sponge kidney may be transmitted as an autosomal dominant trait, but this remains unproven. Most nephrologists consider it a congenital abnormality.
Complications
Occurring in 30% to 60% of patients, complications include formation of calcium oxalate calculi, which lodge in the dilated cystic collecting ducts or pass through a ureter, and infection from dilation of the ducts. Hypertension and renal failure seldom occur, except in patients with severe infection or nephrolithiasis. Secondary impairment of renal function from obstruction and infection occurs in about 10% of patients.
Assessment
Clinical features usually appear only as a result of complications and seldom occur before young adulthood. The patient may complain of severe colic, hematuria, proteinuria, burning on urination, urgency, and frequency—all signs and symptoms of a lower urinary tract infection (UTI). He may also report signs and symptoms of pyelonephritis—sudden onset of chills, fever, dull flank pain, and costovertebral angle tenderness.
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