Kidney and Uretral Stones

Kidney and Uretral Stones

What are stones and the difference between kidney stones and ureteral stones?

Normally, urine contains many dissolved substances. At times, some materials may become concentrated in the urine and form solid crystals. These crystals can lead to the development of stones when materials continue to build up around them, much as a pearl is formed in an oyster.  

Stones formed in the kidney are called kidney stones.  Ureteral stone is a kidney stone that has left the kidney and moved down into the ureter. 

The majority of stones contain calcium, with most of it being comprised of a material called calcium oxalate. Other types of stones include substances such as calcium phosphate, uric acid, cystine and struvite.

Stones form when there is an imbalance between certain chemical urinary components such as calcium, oxalate and phosphate.  These chemical components either promote crystallization while others inhibit it.

The most common stones contain calcium in combination with oxalate and/or phosphate.

A less common type of stone is caused by infection in the urinary tract. This type of stone is called a struvite or infection stone. Much less common are the pure uric acid stones. Much rarer is the hereditary type of stones called cystine stones and even more rare are those linked to other hereditary disorders. 

 What happens under normal conditions?

The urinary tract, or system, consists of the kidneys, ureters, bladder and urethra. The kidneys are two bean-shaped organs below the ribs in the back of the torso (area between ribs and hips). They are responsible for maintaining fluid and electrolyte balance by removing extra water and wastes from the blood and converting it to urine.

The kidneys keep a stable balance of salts and other substances in the blood. They also produce hormones that build strong bones and help form red blood cells. Urine is carried by narrow muscular tubes to the ureters, from the kidneys to the bladder, a triangular-shaped reservoir in the lower abdomen. Like a balloon, the bladder's walls stretch and expand to store urine and then flatten when urine is emptied through the urethra to outside the body.  Normally, urine contains chemicals that prevent crystals from forming.

What are the risk factors for forming kidney stones?

For unknown reasons, the number of people in the United States with kidney stones has been increasing over the past 20 years. Caucasians are more prone to develop kidney stones than African Americans. Although stones occur more frequently in men, the number of women who get them has been increasing over the past 10 years, causing the ratio to change. If a person forms a stone, there is a 50 percent chance they will develop another stone.

Scientists do not always know what makes stones form. While certain foods may promote stones in susceptible people, researchers do not believe that eating specific items will cause stones in people who are not vulnerable. Yet factors such as a family or personal history of kidney stones and other urinary infections or diseases have a definite connection to this problem. Climate and water intake may also play a role in stone formation.

One of the main reasons stones forms is the loss of body fluids or being (dehydrated). When one does not consume enough fluids during the day, the urine can become concentrated and darker. This increases the chance that crystals can form from materials within the urine, because there is less fluid available to dissolve them. Stone formers should maintain 2 liters of urine output every day.  Also, a family history of stones, especially in a first-degree relatives (parent or sibling), dramatically increases the probability of having stones.

Diet can also affect the probability of stone formation. A high-protein diet can cause the acid content in the body to increase. This decreases the amount of urinary citrate, a "good" chemical that helps prevent stones. As a result, stones are more likely to form. A high-salt diet is another risk factor, as an increased amount of sodium passing into the urine can also pull calcium along with it. The net result is an increased calcium level in the urine, which increases the probability for stones. Intake of oxalate-rich foods such as leafy green vegetables, nuts, tea or chocolate may also worsen the situation.

Certain bowel conditions can also increase the risk such as chronic diarrhea, Crohn’s disease, and gastric bypass surgery. Obesity is also an independent risk factor for stone formation.

Although most stone formers do not have a medical condition that directly leads to their stone development, conditions do exist that place patients at high risk for stone formation. For example, stones can form because of obstruction to urinary passage like in prostate enlargement or stricture disease. Stone formation has also been linked to hyperparathyrodism, an endocrine disorder that results in more calcium in your urine. Susceptibility can also be raised if you are among the people with rare hereditary disorders such as cystinuria(formation of cystine stones in the kidneys, ureter, and bladder or primary hyperoxaluria (excessive urinary excretion of oxalate).  Development of kidney stones is due to the excess of the amino acid, cystine or the oxalate in your urine.

Another condition that can cause stones to form is absorptive hypercalciuria, a surplus of calcium in the urine that occurs when the body absorbs too much from food. Another condition that results in a high level of calcium in the urine is resorptive hypercalciuria where the kidney leaks calcium into the urine. The high levels result in calcium oxalate or phosphate crystals forming in the kidneys or urinary tract. Similarly, hyperuricosuria, excess uric acid tied to gout or the excessive consumption of protein-rich products, may also trigger kidney stones. 

Consumption of calcium pills by a person who is at risk to form stones, certain diuretics or calcium-based antacids may increase the risk of forming stones by increasing the amount of calcium in the urine. Calcium oxalate stones may also form in people who have chronic inflammation of the bowel or who have had an intestinal bypass operation or ostomy. This is because of loss of more water from the body as well as absorption of oxalate from the intestine.

What are the symptoms of a kidney stone?

Once stones form in the urinary tract, they often grow with time and may change location within the kidney. Some stones may be washed out of the kidney by urine flow and end up trapped within the ureter or pass completely out of the urinary tract. Stones usually begin causing symptoms when they block the outflow of the urine from the kidney leading to the bladder because it causes the kidney to stretch.

Usually, the symptoms are extreme pain that has been described as being worse than child labor pains. The pain often begins suddenly as the stone moves in the urinary tract, causing irritation and blockage. Typically, a person feels a sharp, cramping pain in the back and in the side of the area of the kidney or in the lower abdomen, which may spread to the groin.

Sometimes a person will complain of blood in the urine, nausea and/or vomiting. Occasionally stones do not produce any symptoms. But while they may be "silent," they can be growing, causing irreversible damage to kidney function. More commonly, however, if a stone is not large enough to prompt major symptoms, it still can trigger a dull ache that is often confused with muscle or intestinal pain.

If the stone is too large to pass easily, pain continues as the muscles in the wall of the tiny ureter try to squeeze the stone along into the bladder. One may feel the need to urinate more often or feel a burning sensation during urination. In a man, pain may move down to the tip of the penis. If the stone is close to the lower end of the ureter at the opening into the bladder, a person will frequently feel like they have not fully completed urination.

Stones as small as 2 mm. have caused many symptoms while those as large as a pea have quietly passed. If fever or chills accompany any of these symptoms, then there may be an infection. You should contact your urologist immediately.

 How are kidney stones diagnosed?

Sometimes "silent" stones, those that cause no symptoms are found on X-rays taken during a general health examination. These stones would likely pass unnoticed. If they are large, then treatment should be offered. More often, kidney stones are found on an X-ray or sonogram taken on someone who complains of blood in the urine or sudden pain. These diagnostic images give the doctor valuable information about the stone's size and location. Blood and urine tests also help detect any abnormal substance that might promote stone formation.

If your doctor suspects a stone but is unable to make a diagnosis from a simple X-ray, he or she may scan the urinary system with computed tomography (CT). CT is an imaging technique that is the gold standard for stone diagnosis as it is an extremely accurate diagnostic tool that can detect almost all types of kidney stones painlessly. Historically intravenous pyelorgram (IVP) was used but this requires prep as well as intravenous contrast dye and serial X-rays.

The above mentioned tests give your doctor information about the size, location and number of stones that are causing the symptoms. This allows the urologist to determine appropriate treatments.

How can kidney stones be prevented?

Unfortunately kidney stones are a recurrent disease, meaning that if you have one stone you are at risk for another stone event. In general, the lifetime recurrence risk for a stone former is thought to approach 50%. Stone prevention, therefore, is essential. Your doctor or urologist may follow up with several tests to determine which factors e.g., medication or diet should be changed to reduce your recurrence risk.

A good first step for prevention is to drink more liquids and water is the best. If you tend to form stones, you should try to drink enough liquids throughout the day to produce at least two liters of urine in every 24-hour period. People who form calcium stones used to be told to avoid dairy products and other foods with high calcium content. However, recent studies have shown that restricting calcium may actually increase stone risk.  High doses of calcium, Vitamin D, or Vitamin C may increase the risk of developing stones, especially in people with a family history of stones. These people need to be careful and should calcium supplementation be needed, calcium citrate is best.

If you are at risk for developing stones, your doctor may perform certain blood and urine tests to determine which factors can best be altered to reduce the risk. Some people can decrease their risk with dietary changes while others will need medicines to prevent stones from forming.

Other general recommendations for stone formers is that they consume a low sodium and low animal protein diet.

Do not be surprised, if you are asked to collect urine for 24 hours after a stone has passed or been removed to measure volume and levels of acidity, calcium, sodium, uric acid, oxalate, citrate and creatinine. This information will be used to determine the cause of the stone. A follow-up 24-hour analysis may be used to find out the effectiveness of treatment. 

How are kidney stones treated?

Stone size, the number of stones and their location are perhaps the most important factors in deciding the appropriate treatment for a patient with kidney stones. The composition of a stone, if known, can also affect the choice of treatments. Options for surgical treatment of stones include:

• Shock Wave Lithotripsy (ESWL)


• Ureteroscopy (URS)


• Percutaneous nephrolithotomy (PNL)


• Open Surgery

Shock Wave Lithotripsy (ESWL^®) Is the most frequently used procedure for eliminating kidney stones. Shock wave treatment uses a machine called a lithotripter. It works by directing ultrasonic or shock waves, created outside your body ("extracorporeal") through skin and tissue, until they hit the dense kidney stones. The impact causes stress on the stone. Repeated shock waves cause more stress, until the stone eventually crumbles into small pieces. These sand-like particles are easily passed through the urinary tract in the urine. The technology is only effective if the kidney is functioning well and there is no blockage to the passage of stone fragments.

ESWL^® is a completely non-invasive form of treatment.  In most cases, shock wave lithotripsy is done on an outpatient basis. Recovery time is short and most people can resume normal activities in a few days. However, one ESWL^® session by itself may not free the ureter of all stone material, and either a repeat ESWL^® session or treatment with another approach may be necessary. ESWL^® is not the ideal treatment choice for all patients. Patients who are pregnant, obese, have obstruction past the stone, have abdominal aortic aneurysms, urinary tract infections or uncorrected bleeding disorders should not have ESWL^®. In addition, certain factors such as stone size, location and composition may require other alternatives for stone removal.

Because of possible discomfort during the procedure, some anesthesia or some form of sedation is generally needed. ESWL^® can be performed under heavy sedation, although general anesthesia has been shown to be associated with a higher success rate. Once the treatment is completed, the small stone particles then pass down the ureter and are eventually urinated away. In certain cases, a stent may need to be placed up the ureter just prior to ESWL to may assist in locating the stone or assist in stone fragment passage following treatment.

Certain types of stone (cystine, calcium oxalate monohydrate) are resistant to ESWL and usually require another treatment. In addition, larger stones (generally greater than 2.5 centimeters) may break into large pieces that can still block the kidney. Stones located in the lower portion of the kidney also have a decreased chance of passage.

While shock wave lithotripsy is considered safe and effective, it can still cause complications. Most patients have blood in their urine for a few days after treatment. Bruising and minor discomfort in the back or abdomen from the shock waves are also common. To reduce the risk of complications, urologists usually tell their patients to avoid aspirin and other drugs that affect blood clotting for several weeks before treatment. Another complication may occur if the shattered stone particles cause discomfort as they pass through the urinary tract. In some cases, the urologist will insert a small tube called a stent through the bladder into the ureter to help the fragments pass.

Ureteroscopy (URS): This treatment involves the use of a very small, fiber-optic instrument called a ureteroscope, which allows access to stones in the ureter or kidney. The ureteroscope allows your urologist to directly visualize the stone by progressing up the ureter via the bladder. No incisions are necessary and general anesthesia is used to keep the patient comfortable during the procedure.

Once the stone is seen through the ureteroscope, a small, basket-like device can be used to grasp smaller stones and remove them. If a stone is too large to remove in one piece, it can be fragmented into smaller pieces. Most commonly this is accomplished with laser energy.

Once the stone has been completely treated, the procedure is done. In many cases, the urologist may choose to place a stent within the ureter, to allow any post-operative swelling or reaction to subside.

Percutaneous nephrolithotomy (PNL): PNL is the treatment of choice for large stones located within the kidney that cannot be effectively treated with either ESWL^® or URS. General anesthesia is required to perform a PNL. The main advantage of this approach compared to traditional open surgery is that only a small incision (about one centimeter) is required in the flank. The urologist then places a guide wire through the incision. The wire is inserted into the kidney under radiographic guidance and directed down the ureter. A passage is then created around the wire using dilators to provide access into the kidney.

An instrument called a nephroscope is then passed into the kidney to visualize the stone. Fragmentation can then be done using an ultrasonic probe or laser. Because the tract allows passage of larger instruments, your urologist can suction out or grasp the stone fragments as they are produced. This results in a higher clearance of stone fragments than with ESWL^® or URS.

Once the procedure is complete, a tube is usually left in the flank to drain the kidney for a period of time, from overnight to several days.

Open surgery: A large incision is required in order to expose the kidney or portion of ureter that is involved with the stone. The portion of kidney overlying the stone or the ureteral wall is then surgically cut and the stone removed.

At present, open surgery is used only in extremely rare situations for very complicated cases of stone disease.

What can be expected after treatment for kidney stones?

Recovery times vary depending upon treatment, with the less invasive procedures allowing shorter recovery periods and quicker return to activity.

Shock Wave Lithotripsy (ESWL^®): Patients generally go home the same day as the procedure and are able to resume a normal activity level in two to three days. Fluid intake is encouraged, as larger quantities of urine can help stone fragments to pass. Because the fragments need to pass spontaneously some pain can be anticipated. It is possible that the stone may not have shattered well enough to pass all of the fragments. If so, a repeat ESWL^® treatment or other options may be required. If a stent was placed prior to ESWL^®, this will need to be removed in your urologist's office within a few weeks. Stents are usually well tolerated by patients but can cause some bladder irritation, frequent urination, and flank discomfort.

Ureteroscopy (URS): Patients normally go home the same day and can resume normal activity in two to three days. As with ESWL^®, if your urologist places a stent, it will need to be removed in approximately 1-3 weeks.

Percutaneous nephrolithotomy (PNL): After PNL, patients usually stay overnight in the hospital. Your urologist may choose to have additional X-rays done while you are still in the hospital to determine if any stone fragments are still present. If some remain, your urologist may want to look back into the kidney with a nephroscope to remove them. This secondary procedure usually can be done through the existing tract into the kidney. Once the stones have been removed, the stent coming out of the flank is removed and the patient can be discharged. Normal activity can be resumed after approximately 1-2 weeks. If a stent was placed, it will need to be removed in 1-3 weeks.

Open surgery: Because these procedures are the most invasive and painful, patients often spend up to five to seven days in the hospital. Full recovery may take up to six weeks.

Postoperatively, your urologist will encourage a high fluid intake, to keep the daily volume of urine produced greater than two liters a day. In addition, you may need to undergo additional blood and urine tests to determine specific risk factors for stone formation and help minimize the chance for future stones. Although stone recurrence rates differ with each individual, a good estimate to keep in mind is a 50 percent chance of redeveloping a stone within a five-year period.

Frequently asked questions:

My stone has not passed, do I need surgery?

In general, you are facing surgery if your stones are large enough to obstruct urine flow, if they are potentially harmful to your kidneys or if they are causing symptoms for which medication does not help.

Will my children get kidney stones because I have them?

Any person with a family history of kidney stones may be at higher risk for calculi. Stone disease in a first degree relative, such as a parent or sibling, can dramatically increase the probability for you. In addition, more than 70 percent of people with certain rare hereditary disorders are prone to the problem. Those conditions include cystinuria, an excess of the amino acid, cystine that does not dissolve in urine and instead forms stones of cystine; and primary hyperoxaluria, an excess production of the compound oxalate, which also does not dissolve in urine, forming stones of oxalate and calcium.

Are gallstones and kidney stones related?

No, there is no known link between gallstones and kidney stones. They are formed in different areas of the body.  If you have a gallstone, you are not necessarily more likely to develop kidney stones.

What is a staghorn stone?

Resembling the horns of a stag, or deer, these stones get their name from the shape they form by filling the pelvis or drainage system of the kidney (at the top of the ureter). Staghorn stones are linked to urinary tract infections. Despite the fact that they can grow large, they are often overlooked by patients because they cause minimal or even no pain. But a staghorn stone can lead to deterioration of kidney function, even without blocking the passage of urine.

Treating this condition can be challenging. In the past, urologists relied on conventional open surgery to remove the offending stone. But today they employ a combination of shock wave lithotripsy and percutaneous surgical procedures, even though patients may still need a traditional operation. ESWL alone is not and effective form of treatment for this type of stone. It is essential once the stone is removed that you work diligently to prevent future stones by preventing urinary tract infections. Luckily, new drugs and the growing field of lithotripsy have greatly improved the treatment of all kidney calculi, including staghorn stones.