Medullary Sponge Kidney

Medullary sponge kidney (MSK) is a congenital disorder with cystic dilatation of the collecting ducts in the renal papillae, associated with nephrocalcinosis and stones.

• Prevalence about 1 in 5,000 to 20,000, found in 12 to 20% of recurrent calcium stone formers; mostly sporadic, familial in 5% (autosomal dominant with variable penetrance, GDNF involvement).
• Usually bilateral but may be unilateral or segmental.
• Associated metabolic abnormalities: hypercalciuria (50%), hypocitraturia, distal renal tubular acidosis (incomplete in 20%), hypokalaemia, impaired urine concentration.
• Associated conditions: hyperparathyroidism, Beckwith-Wiedemann, hemihypertrophy, congenital hepatic fibrosis, Caroli disease.
• Complications: nephrolithiasis, recurrent urinary infections, haematuria, rarely CKD (usually benign course).

• Recurrent renal colic, haematuria (macro or micro), recurrent urinary tract infections in adults aged 20 to 50.
• Often asymptomatic with incidental nephrocalcinosis.
• Mild urinary concentrating defect, nocturia, hypokalaemia (with distal RTA).
• Normal blood pressure and renal function in most.

• CT urography (preferred): contrast "brush-like" striations or "bouquet of flowers" from contrast pooling in dilated tubules, papillary blush, medullary nephrocalcinosis.
• Intravenous urography historically; plain radiograph shows clustered papillary calcifications.
• Ultrasound: echogenic papillae.
• Metabolic evaluation of stone formers: 24-hour urine (calcium, citrate, oxalate, urate, volume, pH), serum calcium, PTH, potassium, bicarbonate, urine pH after acid challenge to detect incomplete distal RTA.
• Exclude other causes of nephrocalcinosis (hyperparathyroidism, distal RTA, sarcoidosis, hyperoxaluria).
• Stone analysis (calcium phosphate or calcium oxalate).

• Asymptomatic: reassurance and observation.
• Stone prevention: fluid intake to urine volume over 2.5 L/day, low sodium diet (under 2 g/day), normal dietary calcium (1000 to 1200 mg), moderate animal protein, limit oxalate-rich foods.
• Potassium citrate 30 to 60 mEq/day in divided doses for hypocitraturia or distal RTA (target urine pH 6.5 to 7.0, urine citrate over 320 mg/day).
• Hypercalciuria: hydrochlorothiazide 25 to 50 mg daily (or chlorthalidone 12.5 to 25 mg, indapamide) with potassium citrate monitoring of potassium.
• Treat urinary infection promptly (culture-guided antibiotics); prophylaxis in recurrent infections.
• Stone treatment: shockwave lithotripsy, ureteroscopic laser lithotripsy, percutaneous nephrolithotomy for large stones; expect residual fragments.
• Monitor annually with creatinine, urinalysis, 24-hour urine, imaging for stones.
• Genetic counselling in familial cases.