Medullary sponge kidney

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.

For example, there may be a high level of calcium, phosphate, and oxalate in the urine, all of which are not very soluble.

In addition, there may be low levels of substances like citrate in the urine which would normally increase their solubility.

Making matters worse, medullary sponge kidney can lead to a metabolic acidosis which can cause calcium to leach out of the bones, which raises the amount of calcium that gets filtered through the kidneys.

Together, the kidney stones and cysts obstruct urine flow, creating pockets of stagnant urine. Those stagnant pools of urine allow more time for solutes to precipitate and crystallize into stones, which creates this vicious cycle of stone formation.

Ultimately, a kidney that is full of cysts and stones with areas of stagnant urine also invites bacteria to flourish - resulting in kidney infections.

So, the symptoms are related to these complications - kidney stones tend to cause bouts of extreme pain and blood in the urine from tissue damage, and urinary tract infections can cause fevers as well as pain.

Medullary sponge kidney is usually diagnosed by medical imagining. For example, an intravenous pyelograms is a type of X-ray that uses contrast to show the enlargement and hyperdensity of the collecting ducts and cysts.

These tend to show a classic “feathered” appearance of the ducts at the interface of the papilla and calyx. Treatment of medullary sponge kidney might target preventing stones from forming, which includes keeping an individual well hydrated, taking citrate supplements to make calcium more soluble, and taking bicarbonate supplements to prevent calcium from getting leached out of the bones.

If small stones develop, they can be broken down with focused shockwaves or surgically removed before they get bigger. Finally, complications like urinary tract infections can be managed with antibiotics.

All right, as a quick recap: medullary sponge kidney is a congenital disorder where the medulla is full of large collecting ducts as well as cysts.

To make matters worse, the nephrons can become dysfunctional allowing high levels of calcium, phosphate, and oxalate in the urine, which can precipitate out and form kidney stones.

Together these cysts and stones can predispose an individual to getting infections. Thanks for watching, you can help support us by donating on patreon, or subscribing to our channel, or telling your friends about us on social media.