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Kidney Stones
What are kidney stones?
Kidney stones are hard, rock-like masses that develop within your kidneys when minerals and chemicals separate from your urine in a crystallized form.
While for most people these crystals pass painlessly and harmlessly through the urinary tract, for some they may aggregate together to create larger structures that can cause extreme pain and, potentially, damage to the kidneys and other structures of the urinary tract.
Stones can develop in the kidneys, which filter excess water and waste from the bloodstream, resulting in urine; in the ureters, which transport the urine to the bladder for temporary storage; and in the bladder itself, where the urine is kept until it can be eliminated through the urethra. Technically, stones may be called ureteral stones or by a number of other names depending on their location and nature. But in common parlance, they are kidney stones.
Kidney stones can be as small as a grain of sand or, at the extreme, grow to be as large as a golf ball. More typically, kidney stones that cause problems can be as small as two millimeters in diameter (conversely, larger stones may pass without any symptoms). Stones that grow large enough can block the flow of urine out of the kidney. More commonly, they move into a ureter, irritating it and causing it to stretch as they pass down its length. Sometimes, they become lodged there. It's the backing up of urine and the resultant stretching of the system that causes pain. It's important to note that some 90 percent of the more common small kidney stones pass out of the body by themselves without invasive treatment.
Treatment options for kidney stones range from as simple as increasing consumption of water with the goal of helping flush them through the urinary tract, minimally invasive treatments such as shock wave lithotripsy, and surgery. Once your type of kidney stone has been identified, medications can be prescribed to help prevent recurrence.
The physicians of Hartford Specialists have extensive experience in the diagnosis and treatment of kidney stones. They employ the latest techniques used in managing, removing and preventing kidney stones.
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How common are kidney stones?
In the United States, kidney stones affect approximately one in every 10 people at some point during their lifetimes, accounting for more than one million cases each year and more than 250,000 hospitalizations.
Kidney stones are more likely to affect men than women (although the number of women developing stones is increasing), and they are most likely to develop in people between the ages of 20 and 40 years. Caucasians are more likely to experience them than African-Americans or Asian-Americans.
Once you've developed one stone, you're 60 percent more likely to have more. If members of your family have had them, your chances of experiencing them are increased as much.
And, while the rates of kidney stone development appears to be increasing at the present time, they are not a new phenomenon. Evidence of kidney stones has been found in a 7,000-year-old Egyptian mummy.
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How does the urinary system work?
The urinary system consists of four elements designed to filter waste from your bloodstream and remove it from your body:
- Kidneys. Not surprisingly, a good description of the kidneys is that they are shaped like large kidney beans, each about the size of a human fist. The nephrons that make up each of the kidneys serve to filter your blood, removing excess water and toxic substances while maintaining a stable balance of salts, glucose and minerals. The kidneys also produce hormones that assist in formation of red blood cells. If healthy, the two kidneys are redundant: if one ceases to function, the other is sufficient to handle the body's needs. This explains why urine output remains adequate even when passing a stone.
- Ureters. The ureters are 10- to 12-inch-long muscular tubes that lead from each kidney to the bladder. Each ureter is about a quarter-inch in diameter. Their walls contract and expand to create movement that propels urine down their length into the bladder.
- Bladder. The bladder is a triangle-shaped chamber with elastic walls that can stretch to store urine and collapse when urine is emptied. Valves at the ureters' entrances to the bladder ensure that urine does not flow backwards toward the kidneys.
- Urethra. The urinary sphincter controls the flow of urine out of the bladder into the urethra, a thin tube through which the urine is eliminated from the body.
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How do kidney stones form?
When the kidneys filter waste substances out of your blood, the urine that results contains a number of minerals and acids that have a propensity for forming crystals, most prominently calcium, oxalate, uric acid and cystine. But urine also normally contains substances that prevent crystal formation, most notably magnesium and citrate. For most people, these substances stay in balance and kidney stones aren't an issue. When adequate amounts of fluids are consumed, the urine remains thin, dilute and clear in appearance.
While the reasons aren't clear, about 10 percent of people experience too-great a proportion of crystal-forming substances, or too-little of the protective ones. The result is a tendency for forming kidney stones.
There are four principal kinds of kidney stones, each associated with different causes:
- Calcium stones. Calcium stones are the most prevalent type by far, representing some 70 to 80 percent of all kidney stones, according to the American Foundation for Urologic Health (AFUD). Calcium stones usually involve a combination of calcium with oxalate or phosphate, developing when the proportions of these substances become abnormally high.
- Uric acid stones. Uric acid is a byproduct of protein metabolism, and can reflect a diet high in meat or other animal proteins. A high proportion of uric acid can also be caused by chemotherapy. Uric acid stones account for five to 13 percent of all stones.
- Struvite stones. Struvite stones are made up of ammonia and magnesium crystals, the product of bacterial enzymes associated with urinary tract infections. In fact, struvite stones are almost always the product of urinary tract infection — and much more common in women than in men. These stones tend to be large and develop with a jagged or staghorn shape in the kidney. Struvite stones account for 10 to 28 percent of all kidney stones, according to AFUD.
- Cystine stones. Cystine stones, which result from a hereditary disorder that causes the kidneys to produce abnormal amounts of some amino acids, account for only one to three percent of kidney stones. These commonly involve many members of certain families.
Other types of kidney stones that can occur include dihydroxyadenine stones, xanthine stones and silica stones, but they are rare. Some drugs can lead to development of kidney stones and kidney infection, such as Crixivan, used to treat AIDS patients.
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What are the risk factors for kidney stones?
Just being a white male between the ages of 20 and 40 with a family history of kidney stones gives you a range of risk factors that you can't do anything about. At the same time, there are some risk factors, such as lifestyle in terms of diet, water consumption and exercise that you can control.
Factors you can't control include:
- Gender. Men are more likely to develop kidney stones than women, although the number of women experiencing stones is rising — for reasons that are not clear.
- Age. You're more likely to develop kidney stones between the ages of 20 and 40 than at other stages of your life.
- Race. Caucasians are more likely to have kidney stones than African Americans or Asian Americans.
- Family history. You're more at risk for kidney stones if your parents, grandparents or siblings have had them than if no one in your family has experienced them.
- Previous kidney stones. If you've already had a kidney stone, your risk of developing additional ones is increased. Some 50 percent of men and 30 percent of women are likely to develop a second stone within five years.
- Hypercalciuria. The cause of stones in more than half of all patients, this inherited trait causes excessive amounts of calcium to be absorbed from food and then discharged into the urine, setting up the formation of calcium oxalate and calcium phostate crystals.
- Diseases and Disorders. Problems such as gout, inflammatory bowel disease, chronic urinary tract infections or intestinal surgery — which may affect the way your body handles calcium and oxalate — increase your risk, as do parathyroid disease, cystic kidney disease, renal tubular acidosis and cystinuria. Persons born with only one kidney may have an increased risk.
A factor you may or may not be able to control is:
- Medications. Some medications may affect your risk of kidney stones, among them calcium-based antacids and some drugs to treat HIV infection. It should be noted that diuretics can decrease the risk for some people. If you are prone to kidney stones, you should discuss the medications you take with your doctor.
Factors you may be able to control include:
- Elevated levels of Vitamin D. Excessive intake of Vitamin D may cause your body to absorb too much calcium. Similarly, calcium added to antacids may represent a risk factor for your body's absorption of excessive calcium.
- Diet. It's important to emphasize that while some foods may promote the formation of kidney stones in people who are prone to them, it's currently believed that eating those foods doesn't cause stones to develop in people who are not otherwise at risk. Specifically, it has been clearly shown that severely restricting calcium-daily-intake actually increases stone formation rates.
That said, for people who are prone to stone formation, the risk of stone formation is actually increased by diets that are high in meat and other protein foods and patients with high sodium (salt) intake. In addition, a diet high in such foods as beets, spinach, strawberries, nuts, chocolate, coffee, tea and cola can play a role in excess levels of oxalates. Apple and grapefruit juices can cause problems.
- Dehydration. If you don't replace body fluids you lose — due, perhaps, to vigorous exercise or simply living or working in a hot environment — with water and other fluids, you run a risk of increasing the proportion of stone-forming components in your urine. Urinating 1½ quarts per day is effective in reducing stone formation. At this level of output, the urine looks clear, not yellow.
- Exercise. Inactivity, such as prolonged confinement to bed or even steadfastly being a "couch potato" can cause your bones to release elevated levels of calcium, increasing the calcium content in your urine.
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What are the symptoms of kidney stones?
For many patients, the first awareness they have of the presence of a kidney stone is extreme pain — often described as the worst pain one can experience. It's also often said to be worse than the pain of giving birth.
Coming on suddenly as a sharp, cramping pain in the back and side, the pain is frequently caused when the stone moves into and through a ureter, where it blocks it completely. As the muscular wall squeezes the stone in its efforts to move it, nausea and vomiting may come on. Blood may show up in the urine.
The pain may vary in intensity in spasms that last from five to 15 minutes. As the stone moves down the ureter closer to the bladder, you may feel a need for frequent — and painful — urination. The pain may extend to your groin as the stone moves farther down. Once it reaches the bladder, however, the pain should pretty much stop.
It's also possible, of course, for you to pass tiny stones with no symptoms at all. And it's possible for a stone in the kidney to be too large to pass into the ureter, creating pain, bleeding or even a blockage at the entrance to the ureter. If a fever or chills develop, it's possible an infection is present, and, if you haven't contacted your doctor already, you should do so quickly. An ineffective, obstructed kidney can be an urgent and serious matter.
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What complications may result from kidney stones?
If a stone is large enough and moves into a position to block the flow of urine from the kidney or in the ureter, it can cause a serious situation beyond the pain that is immediately felt. The back-up of pressure from blocked urine can slowly cause kidney damage. Bleeding and infection are serious possibilities.
The possibility that a blockage has occurred and the flow of urine is being blocked represents a serious emergency that needs to be dealt with immediately. Emergency situations include severe unrelenting pain, severe unrelenting nausea and fevers over 101º. Total blockage of urine can occur rarely in patients with only one kidney or, less frequently, in patients with obstructing stones in both kidneys.
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How are kidney stones diagnosed?
It's possible that a "silent" kidney stone — that is, one that doesn't cause any symptoms — will be discovered during a test for some other issue, but it is more likely that symptoms of pain or blood in the urine will lead your doctor to order any of several tests.
These include:
- Analysis of blood and urine samples to identify the presence of components that may promote stone formation
- X-ray or ultrasound imaging to gather information about the stone's size and location.
- Intravenous pyelography, using a contrast medium (or medical dye) to provide detailed x-ray visualization of the kidneys, ureter and bladder.
- Spiral computerized tomographic scanning with or without a contrast medium to obtain a series of detailed images. This has become a popular and rapid imaging technique.
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How are kidney stones treated?
Treatment for kidney stones depends on the symptoms (especially the degree of pain being experienced), the size and position of the stone or stones and other factors.
Treatment approaches may range from "watchful waiting" (with a dramatic increase in water consumption) to non-invasive treatment with shock wave lithotripsy, the minimally invasive techniques of ureteroscopy and percutaneous nephrostolithotomy, and conventional surgery.
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What is "watchful waiting"?
In many medical problems, "watchful waiting" means simply doing nothing and monitoring the situation carefully. In the case of kidney stones, it means prescribing a dramatic increase in your intake of water to help move the stone along. This presumes the pain is only mild to moderate and can be controlled with routine pain medications, such as ibuprofen.
As many as 90 percent of kidney stones are eliminated naturally through the urinary tract in a period of several weeks. Your doctor will likely ask you to urinate through a strainer (or into a glass in which the stone can be seen) in order to capture the stone for analysis. With information as to the stone's composition, your doctor can prescribe medications or changes in diet to seek to prevent new stones from forming.
However, if the flow of urine through the kidney or ureter becomes completely blocked, then definitive action has to be taken to eliminate the stone.
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What is shock wave lithotripsy?
The "shock" in shock wave lithotripsy (SWL) refers to acoustic sound waves, not to electricity. In this technology, rapid and repetitive sonic waves are generated, passing painlessly and harmlessly through skin and underlying muscle tissue to focus on the hard stone within the kidney or ureter and cause it to break up into tiny grain-size pieces ("lithotripsy" comes from the Greek words for stone and friction). The patient should then be able to pass these grains naturally through the urinary tract.
Some versions of SWL immerse the patient in a tub of water so that the acoustic waves travel through water into the patient's tissues (which are mostly water). Doctors at Hartford Specialists utilize a newer version in which the patient lies on a special stretcher and a water-filled cushion is pressed against the affected kidney.
Lithotripsy can be noisy. The hour-long procedure involves a series of hundreds of loud thumps as the device generates the shockwaves. X-rays or ultrasound are used to monitor the position of your stone in order to ensure that the sonic waves are focused on it. Since passage of a large number of tiny grains can cause discomfort, a channel-opening stent may be placed in the ureter to facilitate their passage. Several months may be required for all the grains to be eliminated.
SWL is usually performed as an outpatient procedure with only a mild anesthetic. Complications can include blood in the urine and bruising in your skin. Additional treatments may be necessary.
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What is ureteroscopy?
A ureterscope is a thin, rigid or flexible fiber-optic scope that can be inserted through the urethra and bladder into the ureter to the site of a stone. With this instrument, the doctor can view the stone directly and use special channels to capture it or break it up with ultrasound or laser energy into smaller pieces for retrieval. Your doctor may place a small cylindrical tube called a stent within the ureter to ensure that it remains open (it will be removed at a later time).
Ureterscopy is usually performed as an outpatient procedure under general anesthesia. Most patients can resume normal activities within several days following the procedure.
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What is percutaneous nephrostolithotomy?
Percutaneous nephrostolithotomy (PCNL) is a minimally invasive surgical procedure that uses a nephroscope, a thin fiber-optic instrument inserted through the side directly into the kidney, to extract stones that can't be treated with SWL or ureteroscopy. Rather than a lengthy open incision, PCN is performed with only a small hole through the skin through which the nephroscope is inserted. A sheath is placed into the kidney and the scope is then used to examine and treat the stones.
If a stone is too large to remove in one piece, the surgeon can use ultrasound or other forms of energy to break it into small pieces for retrieval. Performed under general anesthesia, PCNL generally involves a hospital stay of one or two days, and a recovery time of one or two weeks. A catheter is commonly left in the kidney, exiting below the ribs on the patient's flank.
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What is conventional surgery for kidney stones?
Conventional open surgery is performed today only when other techniques are not feasible. In this procedure the surgeon makes an incision in the patient's flank to access the stone in the kidney or ureter directly. While it is quite effective, it requires a three- to five-day hospital stay and as long as six weeks for recovery.
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What happens following my procedure to eliminate my stone?
If you are passing your stone naturally, your doctor will ask you to capture it by urinating through a sieve or into a cup whose contents can be strained. If your stone has been removed by surgery or an interventional procedure, of course, your doctor should have a sample of it anyway. Capturing it is important so that it can be analyzed to determine what type of stone it is and to work to prevent its recurrence.
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How can I prevent kidney stones?
If you have risk factors for kidney stone formation, you should consult with your physician for an evaluation and information about medications that may prevent their occurrence.
One option is prescription of medications to offset propensities for calcium stones, oxalate concentrations, uric acid stones and cystine stones. These may range from water pills such as hydrochlorothiazide to Allourinol to reduce uric acid.
Another measure for seeking to prevent stone recurrence is drinking plenty of water to keep your urinary system well flushed. Another is dietary modification (see the section on "Factors you may be able to control" above).
Depending on the nature of your stones, dietary modification may be appropriate, pursuing moderation in the ingestion of meat and other protein foods, dairy products and other high-calcium foods. You should not restrict dairy or calcium intake. You may need to avoid a diet high in such foods as beets, spinach, strawberries and nuts. Chocolate, coffee, tea and cola can play a role in excess levels of oxalates. Apple and grapefruit juices can cause problems.
Exercise reduces the tendency for stone formation, so even a moderate program of exercise is desirable.
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For additional information
You can find additional information about kidney stones at web sites sponsored by government agencies, societies and healthcare institutions. It should perhaps be noted that the World Wide Web is open to many sources posting questionable information and promises, and you are encouraged to seek information from established, reputable organizations.
Likely sources include:
American Foundation for Urologic Disease
www.afud.org
American Urological Association Health Guide
www.urologyhealth.org
National Kidney and Urologic Diseases Information Clearinghouse
www.niddk.nih.gov/health/kidney/nkudic.htm
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