Renal Cystic Diseases, Part III

Question 1

Medullary Sponge Kidney

Epidemiology/Pathogenesis

Answer 1

Incidence is likely underestimated because many patients are asymptomatic, but medullary sponge kidney (MSK) is thought to affect 1 in 5,000 people.

Question 2

Medullary Sponge Kidney

Epidemiology/Pathogenesis

Answer 2

Sporadic or familial clustering as autosomal-dominant inheritance with variable penetrance

Thought to involve developmental defect in medullary pyramids and may occur with other developmental defects or tumors

Question 3

Medullary Sponge Kidney

Clinical Manifestations

Answer 3

Generally asymptomatic, incidental finding

May be complicated by hematuria, infections (urinary tract infections), nephrolithiasis (pure calcium phosphate (apatite) or mixture with calcium oxalate)

Question 4

Medullary Sponge Kidney

Clinical Manifestations

Answer 4

Decreased concentrating defect and urinary acidification (incomplete distal RTA with hypercalciuria, hypocitraturia, alkaline urine), the latter leads to bone mineralization defect and stone formation; pre-calyceal duct ectasias

MSK usually does not lead to ESRD.

Question 5

Medullary Sponge Kidney

Histopathology

Answer 5

Bilateral multiple spherical or oval cysts (1 to 8 mm) detected in papillae that may contain apatite concretions and may communicate with the collecting system.

Question 6

Medullary Sponge Kidney

Diagnosis

Answer 6

Abdominal radiographs revealing radiopaque concretions (calcium stones)

Question 7

Medullary Sponge Kidney

Diagnosis

Answer 7

Excretory urography revealing spherical cysts or diffuse linear striations due to contrast retention by dilated medullary and papillary collecting ducts. These findings may also be described as “bouquet of flowers” or “paintbrush” sign.

Question 8

Medullary Sponge Kidney

Diagnosis

Answer 8

Nonenhanced CT may reveal echogenic hyperdense foci in the medulla from stones/nephrocalcinosis.

Question 9

Medullary Sponge Kidney

Management

Nephrolithiasis:

Answer 9

24-hour urine stone risk analysis: e.g., hypercalciuria, hypocitraturia

High fluid intake; potassium citrate 10 to 20 mEq 2 to 3 doses daily to achieve high normal citraturia but with urine pH < 7.5 to avoid calcium phosphate precipitation; thiazides if recurrent stones

Question 10

Medullary Sponge Kidney

Urinary tract infections:

Answer 10

Antibiotics per sensitivity

Aggressive and prolonged therapy is generally recommended, particularly if coagulase-negative Staphylococcus is present.