Medullary sponge kidney
Overview
Developmental cystic disorder of the renal medulla characterised by ectatic distal collecting ducts in the papillary region → stasis, crystal precipitation, nephrocalcinosis and nephrolithiasis.
Classically an adult-onset, often incidental finding in young–middle-aged adults, usually sporadic (rare autosomal dominant familial cases reported).
Kidneys are usually normal sized and overall renal function is often preserved.
Summary
Think “stone-forming adult with medullary duct ectasia” – recurrent calcium stones, medullary nephrocalcinosis, normal-sized kidneys, and often incidental CTU/US/IVU finding.
Associations
- Ehlers–Danlos syndrome (EDS)
- Beckwith–Wiedemann syndrome (BWS)
- HNF1B-related disease (MODY 5)
- Autosomal dominant polycystic kidney disease (ADPKD)
- Caroli disease
- Gitelman syndrome
- Bartter syndrome
- Fabry disease
Clinical Features
Often asymptomatic; when symptomatic, usually in young–middle-aged adults:
- Recurrent nephrolithiasis (calcium phosphate or calcium oxalate)
- Nephrocalcinosis
- Microscopic or gross haematuria
- Recurrent UTIs
- Flank pain / renal colic
- May have incomplete distal renal tubular acidosis (dRTA)
Imaging
CT Urography
- Best current test to demonstrate duct ectasia.
- “Paintbrush” or “Swiss cheese” appearance from contrast-filled, dilated collecting ducts in the medulla.
- Can show medullary nephrocalcinosis and associated stones.
- See also: White pyramid sign (kidney).
Ultrasound
- May show hyperechoic medullary pyramids, with or without visible medullary nephrocalcinosis.
- Kidneys typically normal in size and contour.
Intravenous Pyelography / Retrograde Pyelography (historical)
- Classical but now rarely performed.
- “Bouquet of flowers” and “paintbrush” appearances of opacified ectatic collecting ducts.
