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Medullary Sponge Kidney (MSK) is a congenital, usually non-hereditary malformation of the kidney characterized by cystic dilatation of the collecting ducts of the renal medulla and papillae.

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• It is benign but predisposes to stone formation, hematuria, and urinary tract infections.

![Medullary sponge kidney: The large part of the kidney appears to be porous, like a sponge. An inset shows a microscopic view of a nephron with cysts growing on the tubule. Labels point to the cysts.

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health. ](attachment:2410a161-d8ba-45de-b3b4-febf7cda3341:N00727-H_thumbnail.jpg)

Medullary sponge kidney: The large part of the kidney appears to be porous, like a sponge. An inset shows a microscopic view of a nephron with cysts growing on the tubule. Labels point to the cysts.

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.

Etiopathogenesis

• Embryological defect in the distal nephron (collecting ducts).
• Thought to result from abnormal development of collecting tubules in the medullary pyramids.
• Usually sporadic, but rare associations with Beckwith–Wiedemann, Ehlers–Danlos, and Caroli disease.
• Onset: present at birth but usually diagnosed in 3rd–4th decade.

Associated conditions:

• Ehlers–Danlos syndrome
• Caroli’s disease
• Beckwith–Wiedemann syndrome

Clinical Features

Often asymptomatic, discovered incidentally. When symptomatic:

• Hematuria (microscopic or gross).
• Recurrent nephrolithiasis (calcium stones common).
• Recurrent urinary tract infections.
• Flank pain due to obstruction by stones.