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Medullary Sponge Kidney
Medullary sponge kidney is a rare disease of the kidney
that is present since birth in which cysts (sacs filled
with fluid or partially solid material) cause tubes of the
kidney (known as collecting tubules) to widen.
Collecting tubules (tubules are small tubes) collect urine
from other small tubes in the kidney called convoluted
tubules and pass it through to the renal pelvis.
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The renal pelvis is a flat, funnel-shaped expansion of the top part of the ureter, which is a
thick tube that takes urine to the bladder.
WHAT KIND OF PROBLEMS DOES WIDENING OF THESE TUBES CAUSE?
By increasing the width of the collecting tubules, the normal flow of urine that passes
through them is slowed or stopped. To understand this better, picture trying to pass liquid
through a straw and then trying to pass the same amount of liquid through a large water
pipe. The liquid will enter the straw at the same speed it enters the pipe. However, the
liquid will pass through the straw quicker than the water pipe because there is less room
for it to pass through.
When you increase the size of the object that the liquid is passing through (such as the
large water pipe or the widened collecting tubules), the liquid will spread out, travel
slower, and might eventually stop traveling altogether.
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When the flow of urine is slowed down or stopped, infections and
kidney stones can develop. The infections develop because the
toxins in the urine are not passing out of the body quick enough. In
addition, since urine is warm and bacteria thrives in warm areas,
having a place in the body where warm urine is sitting promotes
bacteria growth.
Kidney stones develop when certain bacteria cause the urine to
become less acidic. When urine is less acidic, two substances in
urine (uric acid and cystine) gather into a mass and form kidney
stones. Thus, one of the ways this disease is treated is by taking
drugs that make the urine more acidic.
WHAT ARE SIGNS AND SYMPTOMS OF MEDULLARY SPONGE KIDNEY?
Signs and symptoms of medullary sponge kidney include excessive urinating and/or a burning pain while
urinating. People with medullary sponge kidney also tend to have abnormal amounts of blood in the urine.
Kidney failure does not usually develop with this condition.
HOW IS MEDULLARY SPONGE KIDNEY DIAGNOSED?
Medullary sponge kidney is diagnosed by using X-rays to examine the urinary system.
HOW IS MEDULLARY SPONGE KIDNEY TREATED?
There is no treatment to get rid of the cysts in the kidneys. This is why treatment focuses on removing and
preventing infections and kidney stones. Infections of the urinary system are treated with antibiotics that
kill the bacteria. Low doses of antibiotics can be taken to decrease the chance of future infection. Kidney
stones can be removed through a surgery known as lithotripsy, which uses sound waves to break apart
the stones into small sandy particles. These small particles can then pass through the urine and outside
the body. Some doctors remove kidney stones by inserting a thin tube (called a ureteroscope) into through
the urethra and bladder to catch the stone and remove it. The urethra is a tube shaped structure in the
body that drains urine from the bladder.
People with medullary sponge kidney should also drink lots of fluids in order to decrease the chance that
substances in the urine can build up in great enough amounts to form kidney stones. Contrary to popular
belief, to reduce kidney stones (which are typically made of calcium) one should NOT decrease the
amount of calcium in the diet, but should actually increase it (for example, 1200 milligrams a day). The
reason why increasing calcium intake decreases kidney stone formation is unclear at this time. However,
some diet changes and medications can reduce kidney stone formation.
WHY IS IT CALLED MEDULLARY SPONGE KIDNEY?
The word "medullary" comes from the Latin word "medulla," meaning "marrow." Marrow is a soft type of
tissue present inside bones. If your break a chicken bone in half and look inside, the pink substance that
you see is marrow. Likewise, inside of the kidney are groups of tissue known as the renal medulla, which
contain many of the small tubes mentioned above. (The word "ren" in Latin means "kidney"). The renal
medulla is made up of cone-shaped masses of tissue called the renal pyramids. Medullary sponge kidney
is a disease of the renal pyramids that make up the renal medulla. The word "sponge" is used to describe
this condition because the widening of the collecting tubules caused give the kidney a spongy feeling and
appearance.
