What is medullary sponge kidney
Medullary sponge kidney also known as Cacchi-Ricci disease, is a birth defect where small cysts (sacs) form either on tiny tubes within the fetus’ kidneys (known as tubules) or the collecting ducts (a channel where urine is collected for removal). These cysts can reduce the outward flow of urine from the kidneys. One or both kidneys can be affected.
In a normal kidney, urine flows through these tubules as the kidney is being formed during a fetus growth. In medullary sponge kidney, tiny, fluid-filled sacs called cysts form in the tubules within the medulla—the inner part of the kidney—creating a spongelike appearance. The cysts keep urine from flowing freely through the tubules. More specifically, the dilations occur in the inner medullary (precalyceal) collecting ducts. These collecting ducts are the terminal region of the nephrons, the individual functional units of the kidney. The inner medullary collecting ducts have the job of delivering urine to progressively larger ducts (ducts of Bellini) that deliver the final urine out of the renal papilla into the minor calyces which connect into the renal pelvis and thence into the ureter to the bladder. One way to think of the inner medullary collecting ducts is as a collection of streams merging and forming a river (duct of Bellini) which leads to a delta (minor calyx) and then a lake (major calyx) and ultimately an ocean (renal pelvis).
In medullary sponge kidney, some inner medullary collecting ducts are dilated markedly and have outpouchings (cysts): blind sacs which begin at the inner medullary collecting ducts lumen but go nowhere – like a hallway someone walled off at one end. It is at the ends of these hallways one finds the stones, free floating and probably trouble. Other inner medullary collecting ducts are not dilated and do not have cystic outpouchings.
Quite apart from the inner medullary collecting ducts dilatation and cysts, the kidneys of medullary sponge kidney have two other abnormalities which mark it as a specific disease. Those inner medullary collecting ducts which are not dilated nor cystic have a multilayered epithelial lining, whereas a normal undilated inner medullary collecting ducts lining is one cell layer thick. The interstitial cells of the renal papillum – the cells between the tubules and vessels – are more numerous than in normal kidneys, and have an immature appearance much like is seen in fetal kidneys.
Medullary sponge kidney is considered a rare disorder. The exact cause is not known and the vast majority of cases do not show a family history. Women are affected by medullary sponge kidney more frequently than men.
Medullary sponge kidney is usually a benign disorder without any symptoms, but it can lead to other problems, such as urinary tract infections (UTIs) and kidney stones, as a result of the urine flow being blocked. Most of the stones in patients with medullary sponge kidney tend to be small and will usually pass spontaneously, but occasionally surgery, ureteroscopy, or lithotripsy may be needed. Overall, medullary sponge kidney patients who produce calcium stones tend to make about twice as many stones as other calcium stone formers.
In many cases, medullary sponge kidney does not cause symptoms or problems, but when it does it usually happens during adulthood. Symptoms of medullary sponge kidney do not usually appear until the teenage years or the 20s. If problems do occur, it can cause pain in the side and back (known as flank pain), abdomen or groin. Other symptoms can include painful or burning urination, cloudy urine, blood in the urine (hematuria), fever, chills and nausea. These symptoms depend on the cause and severity of urinary blockage. Kidney failure occurs in about 10% of people with medullary sponge kidney.
Medullary sponge kidney affects about one person per 5,000 people in the United States. Researchers have reported that 12 to 20 percent of people who develop calcium-based kidney stones have medullary sponge kidney 1.
If you have a history kidney stones or urinary tract infections, your doctor may use an imaging test to help confirm if you have Medullary sponge kidney. Diagnosis may involve a type of x-ray procedure called an intravenous pyelogram (IVP), also called an intravenous urogram. This procedure uses a special dye that is injected to help your doctor visualize the kidneys and look any problems, such as cysts in the kidneys or blockages in the urinary tract. Other possible imaging tests include an ultrasound or computed tomography (CT) scan.
Your doctor may also take blood and urine tests to see how your kidneys are working and to look for any signs of infection. Your doctor may also check to see if there is blood in the urine (hematuria).
Once a diagnosis is confirmed, your doctor will regularly monitor your kidneys for changes in the kidney cysts or signs of recurrent kidney stones and urinary tract infections.
Urinary tract infections are usually treated with antibiotics. Kidney stones can pass through by themselves, or may require surgery if they are too large to pass through. After you are treated, you might be advised on ways to prevent future kidney stones or urinary tract infections, such as increasing fluid intake and getting regular check-ups.
Medullary sponge kidney causes
Scientists do not fully understand the cause of medullary sponge kidney or why cysts form in the tubules during fetal development. Even though medullary sponge kidney is present at birth, most cases do not appear to be inherited. Medullary sponge kidney is believed to be a result of abnormal renal development in utero. More specifically, scientists believe the ureteric bud – which will give rise to the ureters – interacts abnormally with the metanephric blastema tissue in the embryo which will produce much of the kidney substance.
There appears to be a genetic component to medullary sponge kidney disease. Some cases of medullary sponge kidney have mutations in the gene for glial cell-derived neurotrophic factor (GDNF). Recent evidence 2 is that about five percent of patients diagnosed with medullary sponge kidney will have at least one relative with some degree of similar affliction. This kind of familial clustering can suggest an autosomal dominant gene expression or the actions of multiple genes giving that impression 3.
There is an association between medullary sponge kidney and hemihyperplasia, previously known as hemihypertrophy, which is a disorder in which one side of the body grows significantly more than the other side.
Medullary sponge kidney association with the following disease entities have been reported 4:
- Ehlers-Danlos syndrome
- Marfan disease
- Congenital hemihypertrophy/Beckwith-Wiedemann syndrome (rare)
- Caroli disease
Medullary sponge kidney affects all races and geographic regions. Among people who are more likely to develop calcium-based kidney stones, women are more likely than men to have medullary sponge kidney 5.
Medullary sponge kidney symptoms
Many people with medullary sponge kidney have no symptoms. The first sign that a person has medullary sponge kidney is usually a urinary tract infection (UTI) or a kidney stone. Urinary tract infections (UTIs) and kidney stones share many of the same signs and symptoms:
- burning or painful urination
- pain in the back, lower abdomen, or groin
- cloudy, dark, or bloody urine
- foul-smelling urine
- fever and chills
People who experience these symptoms should see or call a doctor as soon as possible.
Medullary sponge kidney complications
Complications of medullary sponge kidney include:
- hematuria, or blood in the urine
- kidney stones
- urinary tract infections (UTIs)
Recurrent nephrolithiasis (kidney stones) is a major complication of medullary sponge kidney which often presents with renal colic, often accompanied by hematuria. Renal stones can result in UTI and urinary tract obstruction.
Medullary sponge kidney rarely leads to more serious problems, such as chronic kidney disease or kidney failure.
Medullary sponge kidney diagnosis
A health care provider diagnoses medullary sponge kidney based on:
- a medical and family history
- a physical exam
- imaging studies
Medical and Family History
Taking a medical and family history can help diagnose medullary sponge kidney. A health care provider will suspect medullary sponge kidney when a person has repeated urinary tract infections (UTIs) or kidney stones.
No physical signs are usually present in a patient with medullary sponge kidney, except for blood in the urine. Health care providers usually confirm a diagnosis of medullary sponge kidney with imaging studies.
Imaging is the medical term for tests that use different methods to see bones, tissues, and organs inside the body. Health care providers commonly choose one or more of three imaging techniques to diagnose medullary sponge kidney:
- intravenous pyelogram (IVP)
- computerized tomography (CT) scan
A radiologist—a doctor who specializes in medical imaging—interprets the images from these studies, and patients do not need anesthesia.
In an intravenous pyelogram also called an intravenous urogram, a health care provider injects a special dye, called contrast medium, into a vein in the patient’s arm. The contrast medium travels through the body to the kidneys. The kidneys excrete the contrast medium into urine, which makes the urine visible on an x-ray. An x-ray technician performs this procedure at a health care provider’s office, an outpatient center, or a hospital. An intravenous pyelogram can show any blockage in the urinary tract, and the cysts show up as clusters of light.
Computerized Tomography Scans
Computerized tomography scans use a combination of x-rays and computer technology to create images. For a CT scan, a health care provider may give the patient a solution to drink and an injection of contrast medium. CT scans require the patient to lie on a table that slides into a tunnel-shaped device where the x-rays are taken. An x-ray technician performs the procedure in an outpatient center or a hospital. CT scans can show expanded or stretched tubules.
Ultrasound uses a device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. A specially trained technician performs the procedure in a health care provider’s office, an outpatient center, or a hospital. Ultrasound can show kidney stones and calcium deposits within the kidney.
Medullary sponge kidney treatment
Scientists have not discovered a way to reverse medullary sponge kidney. Once a health care provider is sure a person has medullary sponge kidney, treatment focuses on:
- curing an existing urinary tract infection (UTI)
- removing any kidney stones
Curing an existing urinary tract infection
To treat a urinary tract infection (UTI), your doctor may prescribe a medication called an antibiotic that kills bacteria. The choice of medication and length of treatment depend on the person’s medical history and the type of bacteria causing the infection.
Removing kidney stones
Treatment for kidney stones usually depends on their size and what they are made of, as well as whether they are causing pain or obstructing the urinary tract. Kidney stones may be treated by a general practitioner or by a urologist—a doctor who specializes in the urinary tract.
Small stones usually pass through the urinary tract without treatment. Still, the person may need pain medication and should drink lots of liquids to help move the stone along. Pain control may consist of oral or intravenous (IV) medication, depending on the duration and severity of the pain. People may need IV fluids if they become dehydrated from vomiting or an inability to drink.
A person with a larger stone, or one that blocks urine flow and causes great pain, may need more urgent treatment, such as:
- Shock wave lithotripsy. A machine called a lithotripter is used to break up the kidney stone into smaller pieces to pass more easily through the urinary tract. The patient may need local or general anesthesia.
- Ureteroscopy. A ureteroscope—a long, tubelike instrument with an eyepiece—is used to find and retrieve the stone with a small basket or to break the stone up with laser energy. Local or general anesthesia may be required.
- Percutaneous nephrolithotomy. In this procedure, a wire-thin viewing instrument, called a nephroscope, is used to locate and remove the stones. During the procedure, which requires general anesthesia, a tube is inserted directly into the kidney through a small incision in the patient’s back.
Medications to prevent future urinary tract infections and kidney stones
Your doctor may prescribe certain medications to prevent urinary tract infections (UTIs) and kidney stones:
- A person with medullary sponge kidney may need to continue taking a low-dose antibiotic to prevent recurrent infections.
- Medications that reduce calcium in the urine may help prevent calcium kidney stones. These medications may include
- potassium citrate
A 24-hour urine test is recommended to help optimize the urinary chemistry in motivated patients with medullary sponge kidney who develop stones. These patients will tend to have a higher incidence of renal leak type hypercalciuria and hypocitraturia than most calcium stone formers. If this is confirmed by the 24-hour urine test, these disorders can be treated with thiazide diuretics for the hypercalciuria and potassium citrate supplements for the hypocitraturia.
Some patients will also have distal type renal tubular acidosis which will demonstrate hypocitraturia and can then be treated with supplemental potassium citrate. The dosage of the potassium citrate should be titrated to approach an optimal 24-hour urinary citrate level (usually greater than 500 mg/24 hours) with a urinary pH around 6.5 if possible. A urinary pH over 7.2 to 7.5 should generally be avoided to minimize the production of calcium phosphate calculi. Serum potassium should also be monitored periodically to avoid hyperkalemia 6.
Medullary sponge kidney diet
The following changes in diet may help prevent urinary tract infections (UTIs) and kidney stone formation:
- Drinking plenty of water and other liquids can help flush bacteria from the urinary tract and dilute urine so kidney stones cannot form. A person should drink enough liquid to produce about 2 to 2.5 quarts of urine every day (2000 mL of urine per day) 7.
- Reducing sodium intake, mostly from salt, may help prevent kidney stones. Diets high in sodium can increase the excretion of calcium into the urine and thus increase the chance of calcium-containing kidney stones forming.
- Foods rich in animal proteins such as meat, eggs, and fish can increase the chance of uric acid stones and calcium stones forming. People who form stones should limit their meat consumption to 6 to 8 ounces a day 8.
- People who are more likely to develop calcium oxalate stones should include 1,000 milligrams of calcium in their diet every day. Adults older than 50 years should consume 1,200 milligrams of calcium daily 7. Calcium in the digestive tract binds to oxalate from food and keeps it from entering the blood and the urinary tract, where it can form stones.
- The potassium citrate supplementation also seems to help minimize the long-term bone loss that is sometimes associated with medullary sponge kidney. This bone loss is thought to be due primarily to the persistent renal leak type hypercalciuria although impaired urinary acidification has also been suggested. There is also a possible association with hyperparathyroidism.
People with medullary sponge kidney should talk with their health care provider or a dietitian before making any dietary changes. A dietitian can help a person plan healthy meals.
Medullary sponge kidney prognosis
Medullary sponge kidney is usually a benign disorder without any serious morbidity or mortality. The majority of patients will have normal renal function throughout their lives. However, renal insufficiency or renal failure may occur in as many as 10% of patients with medullary sponge kidney 4. Renal failure is thought to arise from recurrent severe infections and extensive calculi formation.
A small number of medullary sponge kidney patients will describe chronic, severe pain. This group tends to produce substantially more kidney stones than other medullary sponge kidney patients (3.1 stones per patient per year) and often require multiple hospitalizations for pain control. This suggests that 24-hour urine testing and aggressive metabolic treatment directed at nephrolithiasis prevention may be particularly worthwhile in this group of medullary sponge kidney patients 3. Very rarely, patients may develop renal failure as a result of repeated pyelonephritis or urinary tract obstruction.
In approximately 10% of patients with medullary sponge kidney, major morbidity is caused by repeatedly passing renal stones and by recurrent UTI. Complete obstruction of the kidney by renal stones is rare. Surgery is rarely required to remove the stones because they are usually very small and pass spontaneously.
A patient with medullary sponge kidney is estimated to pass 1.23 stones per year, compared with 0.66 stones per year in other people who form calcium stones.
Some physicians may encounter patients with medullary sponge kidney who describe severe, chronic renal pain but have no manifestation of infection, stones, or obstruction. The source of this pain is unclear. These patients may be treated best by physicians comfortable with chronic pain management.
A grading system has been devised that could identify patients with medullary sponge kidney who are at an increased risk for complications based on intravenous urographic findings 9. Higher grades correlated with more frequent symptomatic stone episodes, number of hospital admissions, and number of procedures required per year. Classifications were as follows:
- Grade 1 – One calyx, unilateral
- Grade 2 – One calyx, bilateral
- Grade 3 – More than one calyx, unilateral
- Grade 4 – More than one calyx, bilateral.
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