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Medullary sponge kidney



Renal system


Renal and ureteral disorders
Bladder and urethral disorders
Renal system pathology review

Medullary sponge kidney


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High Yield Notes
11 pages

Medullary sponge kidney

5 flashcards

USMLE® Step 1 style questions USMLE

1 questions

A 25-year-old female comes to the primary care physician for a follow-up appointment. The patient is currently asymptomatic and denies increased urinary frequency or dysuria. However, she has had multiple urinary tract infections during the past year, each of which resolved with antibiotic therapy. Additionally, the patient has had 3 episodes of calcium oxalate nephrolithiasis treated with conservative measures. She is sexually active, in a monogamous relationship, and uses condoms consistently. Temperature is 37.0°C (98.6°F), pulse is 65/min, and blood pressure is 120/80 mmHg. Physical examination shows no abnormalities. Urinalysis and IV pyelography are obtained and the results are shown below:  

 Color  Yellow 
 Clarity  Clear 
 Erythrocytes  8/hpf 
 Leukocytes  2/hpf 
 pH   5.5 
 Nitrates  Negative 
 Glucose   Negative 
 Protein  Negative 
 Bacteria   None 
 Sediment   None 

Image reproduced from Radiopedia  
Which of the following is the most likely underlying cause of this patient condition?  


Content Reviewers:

Rishi Desai, MD, MPH


Tanner Marshall, MS

Medullary sponge kidney, also known as cacchi-ricci disease is a congenital disease where the medullary part of the kidney, which is deeper inside the kidney, gets loaded with fluid-filled cysts which gives the kidney the appearance of a sponge.

Now, the kidney can be divided into the cortex which is the outer layer and the medulla which is the layer below that.

Kidneys contain millions of tiny nephrons which filter the blood - each of which is like a little tube receiving blood on one end in the cortex.

From there, the nephron dips into the medulla, and then goes back out into the cortex, and finally dips back into the medulla a second time to connect to the collecting ducts which gather up all of the urine. Not every nephron has this exact structure, but a lot of them do.

From there, the urine drains through the papilla which is an inverted cone shaped pyramid, that, like a shower head, pours urine into the calyces, which comes from the latin -calix which means large cup, kinda like a Roman chalice.

From there it enters the renal pelvis which funnels the urine into the ureter, then to the bladder, and then finally leaves the body out the urethra.

Now, medullary sponge kidney has to do with the development of the kidney. So during fetal development, first off you’ve got this structure called the mesonephric duct which is involved in development of urinary and reproductive organs, and during the 5th week of gestation, a little guy called the ureteric bud starts pushing its way into another structure called the metanephric blastema, and together, these two little embryologic structures go on to develop into a kidney.

At about the 7th week, nephrogenesis, or formation of the kidneys, starts under the influence of that ureteric bud.

By about 20 weeks, the ureteric bud has formed the ureters, the renal calyces, collecting ducts, and collecting tubules, while the metanephric blastema develops into the nephron itself, which includes the epithelial cells and the podocytes of Bowman’s capsule.

In the third trimester and throughout infancy, the kidneys continue to grow and mature.

Although not completely known, it’s thought that medullary sponge kidney is a result of some sort of abnormal induction of the metanephric blastema by the ureteric bud.

This failure might be the fault of the mesonephric duct not forming right, or the ureteric bud not forming right, or both.

Whatever the case, in medullary sponge kidney, the hallmark feature are dilated collecting ducts, meaning enlarged, as well as small cysts that form around the collecting ducts.

Even though medullary sponge kidney is present at birth, sometimes complications don’t emerge until adulthood, and even then, they might come and go.

The most common one is nephrolithiasis, or developing kidney stones, which are made of calcium phosphate or calcium oxalate. These form in the collecting ducts and surrounding tissue, and these result mostly from a failure of kidney cells to properly reabsorb or secrete solutes which ultimately results in stone formation.

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