Introduction
Kidney stones or calculi are solid collections of urinary components that have formed crystals, precipitated out of the urine and formed into stones. The medical term for the presence of kidney stones is nephrolithiasis. Most often, stones are calcium based but there are many other types of stones that may form. The five most common stone types are calcium oxalate, calcium phosphate, uric acid, struvite, and cystine. Pain from stones can develop when the stones obstruct any part of the urinary system. This article will discuss the different types of stones, risk factors for forming stones, and the treatment and prevention of calculi.
Relevant anatomy:
The urinary tract has several main components: the kidneys, which form the urine, the ureters which transport the urine to the bladder, which then stores the urine until it passes out of the body through the urethra.
The
kidneys are paired, bean-shaped organs, located in the back, just below
the ribs. They serve multiple functions in the body, but primarily the
kidneys filter the blood to clear toxins and extra water from the body
by producing urine. Blood is filtered by a specialized structure called
the glomerulus. Filtered blood from the glomeruli passes into a
complex and highly specialized tubular system that runs through the
kidney called the nephron, which adjusts the concentration of the urine,
and is responsible for the excretion or absorption of the various
electrolytes, such as sodium and potassium. There are two main parts of
the kidney.
The
cortex is the outer portion of the kidney where all the specialized
filters (glomeruli) and tubular structures (nephrons) that filter the
blood and concentrate the urine are located. The collecting system is
where the urine empties before passing down the ureters, which are the
long thin tubes (usually 25-30cm) that channel the urine into the
bladder. The collecting system is comprised of a branch network of
structures called calyces which all empty into the renal pelvis which
then funnels the urine into the ureters. Stones may be located in any
of these structures. Pain may result from obstruction in any location
in the collecting system of the kidney or the ureters. However, the
most common cause of pain from kidney stones arises when the stones pass
down the ureter toward the bladder. There are three narrow areas in
the ureter which typically cause stones to get stuck and cause
obstruction. The first is called the ureteropelvic junction, which is
where the ureter and renal pelvis join. The second narrowed area is
where the ureter passes over the large blood vessels in the pelvis
called the iliac artery and vein. The final, and narrowest portion of
the ureter, is at the ureterovesical junction where the ureter empties
into the bladder.
How common are kidney stones and what are the risk factors for forming them?
Kidney stones are believed to affect roughly 5-10% of the population. They more commonly develop in men by about a three to one margin and are more frequent in Caucasians than African-Americans. Once a person forms one kidney stone, the likelihood of experiencing a recurrence is about 10-15% in one year and nearly 50% by 5 years. The incidence varies in different parts of the world with the United States, much of Europe, Scandinavia, and China having a relatively high incidence of stones, and much of Central and South America and Africa thought to have lower incidence of stones, but this may be secondary to lower detection rates. Risk factors for the formation of kidney stones include inadequate fluid intake, a diet high in salt and/or animal protein, urinary tract infection, family history of kidney stones, and a variety of other disease states such as primary hyperparathyroidism. When the usual components of urine become either too high or too low in concentration, stone formation is more likely. Elevated levels of calcium (hypercalciuria), oxalate (hyperoxaluria), and uric acid (hyperuricosuria) can all lead to stone formation. Abnormally low levels of citrate (hypocitraturia) and total urine volume can also lead to the development of stones.
How do kidney stones form?
The kidneys are essential to sustain life and their principal function is to filter the blood to excrete bodily waste products that accumulate from our diet and normal metabolic processes. When the concentration of various components of the urine such as calcium and oxalate becomes too high, crystals can form in the urine and over time, these crystals can group together with a small amount of an organic material called matrix, to form stones. There are multiple substances in urine that can form stones if the concentration becomes too high, including calcium, oxalate, and uric acid. To combat this process, however, normal urine contains several inhibitors of stone formation including citrate, magnesium, and several proteins. In patients who form stones, the balance between the promoters and inhibitors of stone formation shifts towards stone formation. Once a solid stone forms, it may remain stable in size or it may continue to grow. The exact mechanism for how a stone initially forms, however, is still unclear.
Signs, Symptoms, and Diagnosis
In many instances, stones can be present in the kidney or ureter and be asymptomatic if they are not obstructing the flow of urine down towards the bladder. When the stone obstructs the flow of urine, either in the kidney or the ureter, the collecting system behind the stone stretches, resulting in pain. Pain from a stone is often referred to as colic as it is usually intermittent in nature. Patients with stone-related pain often move around trying to find a comfortable position to alleviate the pain. This is in contrast to other causes of abdominal pain, such as appendicitis, where patients try to remain still to prevent the pain from getting worse. Pain from a stone can be quite severe and may be associated with nausea and vomiting. Pain from an obstructing stone in the kidney or proximal ureter is often located in the back or flank or upper abdomen on the affected side. As the stone progresses down the ureter, the location of pain can shift as well. As the ureters become narrow over the iliac vessels in the pelvis, stones often can get stuck and pain from stones in this location can be in the lower abdomen, groin, testes, or labia. As the stone moves into the distal ureter and approaches the bladder, it often gets held up at the ureterovesical junction, which can cause bothersome urinary frequency, urgency, and sometimes pain at the tip of the penis. If there is an infection related to the stone, fever and chills also may also develop.
Patients
presenting with symptoms potentially caused by a kidney stone should be
evaluated with several tests. A urinalysis often will demonstrate some
blood in the urine, or hematuria, although the absence of blood does
not exclude a stone. The urinary pH may also provide a clue as to what
is causing the stone. The urinalysis can also help to determine if
there is an infection associated with the stone. Several blood tests
may be obtained, including a serum creatinine which is a measure of
overall kidney function. An elevated creatinine can be indicative of a
significant obstruction and/or dehydration if patients have been
vomiting from stone-related pain. A white blood cell count also can be
useful as an elevated value can be indicative of infection.
There
are several diagnostic imaging modalities which can be used to evaluate
for the presence of stones. A plain x-ray of the abdomen can identify
many stones, however some stones, such as those composed of uric acid,
are typically not visible on plain x-ray. An example of a large,
staghorn type stone is shown in Figure below.
Furthermore, small stones may be obscured by overlying structures and gas in the digestive tract. Ultrasound can be a useful modality and does not cause any radiation exposure to the patient. Ultrasound is useful for determining the presence of swelling of the kidney from obstruction (hydronephrosis), and can visualize most stones in the kidney. Ultrasound, however, misses many stones in the ureters. Computed tomography (CT) scanning has become much more widely utilized in the evaluation of stones. A non-contrast CT scan can be performed safely in most patients and can detect every stone type except rare stones caused by protease inhibitors, medications used to treat HIV-positive patients. It also provides useful information about the anatomy of the kidney and size and location of stones to help plan a possible surgical procedure. A CT scan showing a large left kidney stone is shown in Figure below.
A CT scan also may be useful in diagnosing other intra-abdominal pathology which could be the source of pain. Magnetic resonance imaging (MRI) is sometimes used in the evaluation of abdominal pain but MRI and does not cause any ionizing radiation exposure to the patient but in general, MRI, especially without intravenous contrast, is not a reliable technique for visualizing stones.1,2
Developing one kidney stone suggests a high likelihood of developing a new stone. To aid in stone prevention and to determine the likely underlying risk factors, a metabolic work-up can be obtained. This includes several blood tests, including calcium, uric acid, and parathyroid hormone. The metabolic evaluation also includes a 24-hour urine collection which is useful to determine what the underlying risk factors are, such as low urine volume, high urine levels of calcium, oxalate, uric acid, or low levels of urinary citrate. Based on this data, the urologist may recommend dietary changes and/or pharmacologic therapy to help reduce the risk of stone recurrence.3
What are the major stone types, what are the causes, and how are they medically treated?
There are five major stone types: calcium oxalate, calcium phosphate, struvite (magnesium ammonium phosphate), uric acid, and cystine. Each type of stone has a distinct crystal shape, as depicted in Figure 5.
Calcium oxalate crystals are square shape with a characteristic “X” mark, struvite stones have a “coffin lid” appearance, uric acid crystals are often needle shaped and can form into rosettes, and cystine crystals are hexagonal in shape. Calcium-based stones (calcium oxalate and calcium phosphate) are the most common, comprising about 85% of stones, and calcium oxalate stones are the most prevalent.
1) Calcium Stones:
There
are several metabolic abnormalities that lead to the development of
calcium stones. The most common of these is hypercalciuria or elevated
calcium levels in the urine. Hypercalciuria can be classified into
three different types which are absorptive, resorptive, and renal. In
absorptive hypercalciuria, there is an excess of calcium absorbed from
the digestive system, mainly the small intestine. The majority of cases
of absorptive hypercalciuria are not dependent on calcium intake. Thus,
limiting calcium intake will not fix the problem, contrary to what many
believe.4 There are medications
available that can correct the elevated urinary calcium of absorptive
hypercalciuria. Cellulose phosphate is an agent that when taken with
meals, binds to calcium in the intestine so it is excreted in the stool
instead of going into the urine. Another option is a thiazide diuretic
such as hydrochlorothiazide, which decreases the excretion of calcium by
the kidney into the urine but does not affect the digestive system.
There are a minority of cases of hypercalciuria that are calcium
dependent and a metabolic evaluation (see diagnosis) is necessary to
determine if a calcium restricted diet may be beneficial. Resorptive
hypercalciuria occurs when there are elevated levels of parathyroid
hormone in the circulation, often from an abnormal growth in the
parathyroid gland, which leads to calcium being reabsorbed from the
bones, resulting in elevated calcium levels in the blood and eventually
in the urine. The primary treatment of this disorder is by surgical
removal of the abnormal parathyroid gland. Renal hypercalciuria is an
intrinsic problem in the kidney which leads to inadequate reabsorption
of calcium from the urine. Thiazide diuretics are the mainstay of
treatment for this abnormality.
In addition to
hypercalciuria, there are several other causes of calcium stone
formation. Elevated levels of uric acid in the urine, or
hyperuricosuria, can be a contributing factor and can be caused by an
excess of purines in the diet or an abnormality of uric acid
metabolism. Foods that are high in purines include very rich foods like
sweetbreads, liver, kidney, sardines, and anchovies. Most meat, oily
fish, and shellfish have moderately high amounts of purines so eating
these foods in moderation is important in patients with
hyperuricosuria. Several vegetables and
grains also contain moderate amounts of protein but it appears, at least
in gout which is also uric acid dependent, that purines from vegetable
sources are not as problematic as from animal sources.5 Calcium
stones that form in the presence of high uric acid are different than
true uric acid stones as these stones are usually a combination of uric
acid and calcium and patients do not have the characteristic low urine
pH as is seen with pure uric acid stones.
Elevated
urinary oxalate, or hyperoxaluria, is caused by abnormal absorption of
oxalate from the digestive system. Oxalate is found naturally in many
foods we eat. Normally, calcium in the diet binds with the oxalate
which then is excreted in the stool. In patients with various types of
digestive problems such as chronic diarrhea, inflammatory bowel disease,
or patients who have had gastric bypass surgery, there is an increase
in the amount of fat passing through the intestines and this binds with
calcium, thus making the calcium unavailable to bind with oxalate. This
leads to increased amounts of free oxalate in the intestines which are
absorbed and excreted into the urine, which can result in a higher
likelihood of stone formation. There are two primary methods to help
decrease urinary oxalate in patients with hyperoxaluria. One method is
to have patients take extra calcium with their large meals by having a
serving of dairy or by a calcium supplement which will then bind the
excess oxalate. The other method of reducing oxalate is to restrict the
amount of oxalate in the diet. Many foods contain oxalate but the most
common foods that should be restricted include dark green vegetables
such as spinach, chocolate, and nuts. Caution must be taken when
attempting to make dietary changes to reduce oxalate to ensure that the
new foods do not have just as high or even higher oxalate content as the
previous diet.
Abnormally low levels of urinary
citrate, known as hypocitraturia, also can lead to calcium stone
formation. Citrate is a natural inhibitor of kidney stones as it binds
calcium, making it unavailable to form stones. Hypocitraturia can be
caused by any condition that causes an acidosis, when the pH of the
blood is abnormally low. There are many causes of acidosis but a few
examples include chronic diarrhea, type I renal tubular acidosis, and
prolonged fasting. Urinary citrate levels can be increased by citrate
supplementation, usually in the form of potassium citrate which can be
taken as tablets or crystals mixed into liquids. Alternatively,
lemonade has been shown to increase levels of urinary citrate as well
and can be an option in patients who do not want to take medications.6
2) Uric acid stones
Uric acid stone formation is dependent on the pH of the urine. The
average urinary pH in the general population is around 5.85 and patients
that form uric acid stones consistently have urinary pH values of less
than 5.5. At this pH, uric acid crystals can precipitate out of the
urine and form stones. Therefore, the treatment of uric acid stones is
aimed at increasing the urinary pH, also known as alkalinization.
Potassium citrate is the most commonly used medication and the goal of
therapy should be to get the pH between 6 and 6.5. If the pH gets too
high, calcium phosphate stones may occur. If treatment is successful,
uric acid stones can be dissolved without surgical intervention, which
is not true of calcium-based stones. With proper alkalinization of the
urine, about 1cm of stone can dissolve per month and with continued
alkalinization, uric acid stones can be eliminated completely. Several
disease states, including myeloproliferative disorders and malignancies,
can lead to elevated uric acid levels in the blood and can lead to uric
acid stones. Elevated uric acid levels in the blood can be corrected
with allopurinol, which is the same medication used in the prevention of
gout.
3) Struvite stones
Struvite stones, also known as magnesium-ammonium-phosphate or
infection stones, are stones that form as a result of urinary tract
infection. The bacteria that can lead to struvite stones are known as
urea-splitting organisms, the most common of which are Proteus, Pseudomonas, and Providencia.
The pH of the urine in patients with struvite stones is usually
elevated, higher than 7.2, which leads to the precipitation of the
magnesium-ammonium-phosphate stones. The only effective means to
eradicate the infection in patients with struvite stones is to
completely remove the stones. Struvite stones, unlike calcium-based
stones, rarely present with renal colic and often are asymptomatic until
they become very large and infections develop. Therefore, treatment of
the stones often requires invasive surgery to clear the stone burden.
4) Cystine stones
Cystine stones are the result of a defect in one of the amino acid
transporters in the kidney and intestine causing abnormally high levels
of cystine to be excreted in the urine. This is thought to be an
autosomal recessive disorder, meaning that both parents have to be
carriers of the defective gene and a child has a 25% chance of
inheriting the disease. There are no known inhibitors of cystine stone
formation so prevention is based primarily on increasing fluid intake
(enough to have 3-4 liters of urine per day), alkalinizing the urine to
above 7.5, and several medications that are thought to bind to cystine
to prevent stone precipitation. However, many patients have
difficulties complying with these difficult preventative measures. Even
with good compliance, there is a high likelihood of frequent stone
recurrences.
Unusual types of stones
There
are several other types of stone which are much less common than the
five listed above. Two of these, 2,8-dihydroxyadenine and xanthine
stones, are often the result of a genetic defect. A variety of
medications can also form stones if taken in large enough amounts.
Guaifenesin, a common drug found in cough and cold remedies, can form
into stones as can ephedrine, another medication used for congestion and
colds. Sulfa from various antibiotics can form stones as can
topiramate (Topamax), a medication used for seizures. The protease
inhibitors indinavir and nelfinavir, used in the treatment of HIV, can
also form stones and indinavir stones are unique in that they are the
only stones that are not visible on non-contrast CT scan.
How Can I Change My Diet to Prevent Stones?
There
are three general guidelines that are useful for all patients hoping to
prevent the formation or recurrence of kidney stones. The first is
adequate fluid intake so that the patient urinates between 1.5 and 2
liters of urine per day. The second is a diet low in sodium. A diet
high in sodium leads to higher levels of calcium excreted in the urine
and a higher likelihood of stone formation. Finally, spacing out animal
protein intake over the course of several meals is important as a
single meal high in animal protein will cause the blood to become acidic
which causes calcium to be reabsorbed from the bones, leading to
transiently high urine calcium levels. For more patient-specific
recommendations, the previously discussed metabolic evaluation is
necessary.
Medical Expulsion Therapy:
As
mentioned previously, stones are symptomatic when they cause
obstruction of the urinary tract. The most common location for a stone
to get stuck and cause obstruction is in the ureter. Patients
presenting with small ureteral stones often will be able to pass the
stone without any surgical intervention so management of the symptoms is
the mainstay of treatment. Narcotic pain medications such as Percocet
or Vicodin are often utilized for pain control and patients should be
aware that these medications must be used with caution and should not be
used while driving. In the setting of acute pain, many patients often
present to the emergency department or are admitted to the hospital and
in this setting, ketorolac (Toradol), given intravenously or
intramuscularly, is a very useful medication as it works very well as
both a pain reliever and anti-inflammatory. In addition to pain
medication and anti-nausea medication, several other medications can be
useful to aid in stone passage. One class of medications which has been
shown to aid in stone passage are the alpha-blockers which are often
used in the management of benign prostatic hyperplasia.7
Examples of alpha-blockers include tamsulosin (Flomax) and alfuzosin
(Uroxatral), which help to relax the smooth muscle in the ureter and can
be taken daily. The second class of drugs utilized is steroids, which
work by decreasing inflammation and swelling. Steroids
can have multiple side effects if used long term so typically a short
course (typically 3 days) is given, often in combination with an
alpha-blocker.8 Finally, non-steroidal
anti-inflammatory medications such as ibuprofen or naproxen not only
help with pain but also limit inflammation. The use of some or all of
these medications in combination can increase the chances of spontaneous
stone passage from the ureter into the bladder. The likelihood of a
stone passing depends primarily on the location and the size of the
calculus, with stones less than about 5mm having a much higher chance to
pass than larger stones. Once in the bladder, stones pass easily
through the urethra and out of the body as the caliber of the urethra is
much larger than the ureter. Patients trying to pass a stone are often
encouraged to strain the urine so if the stone passes, it will be
available for stone analysis to determine its composition.
Emergent Indications for Intervention:
Many
patients who are passing a kidney stone can be managed with medications
and observation. However, there are three main indications for more
urgent intervention. One is if a patient develops a fever or other
signs of infection. Severe kidney infections can occur if there is a
stone completely obstructing an infected kidney. The second is if the
pain is causing such severe nausea and/or vomiting that a patient is
unable to tolerate any food or liquids. The third is if the pain is
uncontrollable with oral pain medications. While this may not always be
an indication for emergent surgical intervention, it does mean that
patients need to be admitted to the hospital for intravenous pain
control. The most common surgical modalities for the relief of
obstruction from a stone is the placement of a ureteral stent or a
nephrostomy tube which will be discussed in detail in the next section.
Surgical Management of Stones:
There
are multiple options for the treatment of symptomatic kidney stones
that are not able to pass out of the urinary system on their own. In
the developed world, most current stone treatments are minimally
invasive with very small incisions, or none at all.
For
patients with severe pain who have other medical issues which prevents
them from undergoing definitive surgery, or if the necessary equipment
is unavailable, temporary relief of the obstructed system can be
accomplished by placement of either a ureteral stent or a nephrostomy
tube. A stent is a small plastic tube with a curl on either end that is
placed into the ureter to allow the urine to bypass the obstructing
stone (Figure 6).
This relieves the obstruction but some patients have bothersome symptoms related to the presence of a stent in their bladder. When a stent is placed, the urologist has the option to leave a small string attached to the stent which allows for removal of the stent at a later date without the need for an additional procedure. The string comes out the urethra and when the stent is ready to come out, the patient or doctor simply pulls the string to remove the stent. If no string is left in place, a cystoscopy, where a small scope is placed into the bladder, must be performed to remove the stent with small graspers. Another option in the more urgent setting is the placement of a nephrostomy tube. This is a small tube which is placed directly into the kidney from the back and is an effective means to relieve an obstructed kidney. A nephrostomy tube, however, has the disadvantage of being an external tube connected to a drainage bag so it can impact a patient’s quality of life.
Shock wave lithotripsy
(SWL) is a non-invasive treatment that utilizes shock waves to break up
stones into small pieces so that they may pass on their own. There are a
variety of different machines in use today but the basic concept is
similar for all of them. Similar to a thunderstorm where an electric
current (lightning) causes a shock wave (thunder), SWL machines all are
able to produce shock waves that are targeted at the stone. The effect
of multiple shocks is additive and stones are often administered up to
3000 shocks during one procedure. These procedures can be performed
either with a general anesthetic or with intravenous sedation. The
procedure consists of placing the patient onto a special machine called
the lithotriptor. The stone is then targeted with the fluoroscopy
(x-rays), ultrasound, or a combination of the two. Once the stone is
identified, the shock waves are administered to the stone. After the
stone is fragmented, all the tiny fragments will pass down the ureter
and into the bladder and eventually will be passed out of the body with
urination in an uneventful fashion. Most of the stone fragments pass
within the first two weeks after SWL. Occasionally, an obstruction can
occur from a large number of stones getting stuck in the ureter while
attempting to pass into the bladder. This condition is known as
steinstrasse (stone street in German) and may require the placement of a
nephrostomy tube. SWL is effective for stones up to about 2 cm in size
that are located in the upper pole of the kidney or the renal pelvis,
and has decreased success with larger stones or stones located in the
lower pole of the kidney which makes it difficult for the fragments to
pass.9 Also, some types of stones
are harder and more resistant to shock waves but it is often not
possible to tell what the stone is made of pre-operatively. SWL is a
safe and effective procedure and the main complication is bleeding from
the kidney, which only rarely can be significant. Currently, there is
no convincing data that shows any long term kidney damage after SWL with modern lithotripters.
Ureteroscopy is another method for treating stones in the
kidney or ureter. Ureteroscopy is generally performed under general
anesthesia but can be performed with a regional anesthetic. There are
no skin incisions during the procedure as it is all performed through
the urethra. The initial step involves placement of a scope called a
cystoscope into the bladder. Once in the bladder, the opening in the
bladder where the ureter enters, called the ureteral orifice, is
identified. Typically, a small guidewire is then placed into the ureter
to allow for placement of the smaller caliber ureteroscope. For stones
in the lower portion of the ureter, the urologist may use a semi-rigid
ureteroscope to visualize the stone and then either remove it or
fragment it into smaller pieces. Figure 7 shows the appearance of a
stone in the ureter as seen through a ureteroscope.
For stones in the more proximal portion of the ureter or the kidney, the flexible ureteroscope is utilized. This is a very thin scope that flexes at the tip to allow access into all parts of the kidney. Once stones are visualized through the ureteroscope, there are multiple options for removing them. There are a wide variety of graspers and basket devices which can be used to grab the stones and pull them out of the kidney or ureter. If the stones are too large to be removed, they must be broken into smaller fragments. This can be accomplished with an electrohydraulic lithotriptor (EHL) which uses shock waves to fragment the stone, a pneumatic lithotriptor which is like a small jackhammer on the stone, or most commonly with a laser. The type of laser used most frequently is called the Holmium laser, and it has been proven to be safe and effective in the treatment of stones. Once the procedure is complete, a ureteral stent is often left in place as the ureteral orifice may develop swelling from the passage of the scope and lead to kidney obstruction. In many cases, a stent is left for several days after surgery with a string attached so that it may be removed without an additional procedure. However, the string itself may be irritating so the urologist may elect to remove it. Furthermore, if there is any concern about a narrowing or stricture of the ureter, or if the ureter was dilated to allow access for the scope, the stent may be left in place for a longer period of time and in these cases, the string is normally removed prior to placement. The main risks of ureteroscopy include bleeding, infection, and injury to the ureter, but fortunately these are rare complications.
Percutaneous
nephrolithotomy or PNL is a procedure that is often utilized for larger
or more complex stones. In this procedure, an access needle is placed
directly into the kidney using radiologic guidance. This is typically
performed through a small incision in the back and once the needle is
introduced, a guidewire is placed through the needle into the kidney and
used to dilate the tract to allow for the placement of a rigid scope,
called a nephroscope, directly into the kidney (Figure 8).
Once the nephroscope is in the kidney and the stone(s) is identified, it can be removed with a grasper or fragmented with a variety of devices. The advantage of a percutaneous approach in the treatment of stones, especially large stones, is that after the stone is fragmented, the pieces can be removed or evacuated using a suction device to truly get the patient stone-free prior to leaving the hospital.
A short video of a percutaneous stone procedure using an ultrasonic lithotriptor.
After the procedure, a small tube is typically left in place for a period of time, and is subsequently removed. Recently, some urologists have begun performing a “tubeless” technique where there is no tube left in the back after surgery but a stent is placed into the ureter instead.10 This has the advantage of the patient not having any external tubes protruding out the back, but has the disadvantage that a second procedure is often required to remove the stent. If stones are very large or if infection is encountered during the access into the kidney, a nephrostomy tube can be left in place and the patient can be brought back for an additional procedure at a later date. Some complex stones may require multiple procedures and/or multiple tracts in the kidney to remove the extensive stone burden. The main risks of PNL are bleeding, infection, and injury to adjacent organs which can include the bowels, spleen, liver, or the pleura of the lungs. Again, the incidence of these injuries is very low and the vast majority of cases are uncomplicated.
Laparoscopic
approaches can also be used in special stone cases. This involves
making several small incisions in the abdomen or flank, inflating the
abdomen to allow for adequate working space, and using a camera and
long, thin instruments to perform the procedure. For large stones in
the renal pelvis, the area where the collecting system funnels into the
ureter, a laparoscopic pyelolithotomy can be performed, in which an
incision is made into the renal pelvis and the stone is removed.
Laparoscopy also can be utilized for kidneys stones in a caliceal
diverticulum which is a small outpouching from a calyx where the urine
collects. These diverticuli often have narrow openings and the stones
can be very peripheral in the kidney. In this circumstance it may be
easier to remove the stone from outside the kidney via laparoscopy,
rather than from inside the kidney.
In rare cases
in the developed world, but more commonly in developing countries,
kidney or ureteral stones can be removed via an open approach, using
relatively large incisions to gain access to the stone. These incisions
can be in the side, back, or lower abdomen, depending on the stone’s
location. These approaches can be performed with basic, reusable
surgical instruments that are used in other surgical procedures. These
procedures, while effective, often result in more post-operative pain
and longer recovery times than the minimally invasive alternatives.
Stones in Pregnancy
Kidney
stones in pregnant women can present a difficult management problem.
There are several physiologic changes that occur in the kidneys during
pregnancy that may lead to the development of kidney stones. However,
the overall incidence of stones is not increased in pregnant women
compared with non-pregnant women of the same age. Ultrasound is the
primary diagnostic modality, as all attempts should be made to limit
radiation exposure to the fetus. Most stones occur during the 2nd and 3rd
trimesters and the majority can pass on their own without
intervention. However, for severe symptoms, pregnant patients can have
ureteral stents of nephrostomy tubes placed to decompress the obstructed
system. Ureteroscopy and laser lithotripsy is also safe in pregnancy,
but shock wave lithotripsy is contraindicated.
Conclusions:
Kidney
stones are a common problem, affecting nearly 10% of the population,
and once a patient develops a stone, the risk of a recurrence is high.
The majority of stones are calcium based and may be asymptomatic but if
they cause pain or obstruction, they must either pass out of the urinary
system on their own or be removed surgically. A metabolic evaluation
can determine a patient’s individual risk factors but in general, a low
salt diet and adequate fluid intake can help prevent stones from
recurring.
References:
- Rao PN: Imaging for Kidney Stones. World J Urol 2004;22:323-327.
- Sudah M, Vanninen RL, Partenen K, et al: Patients with Acute Flank Pain: Comparison of MR Urography with Unenhanced Helical CT. Radiology 2002;223:98-105.
- Chandhoke PS: Evaluation of the recurrent stone former. Urol Clinics of North Am;34:315-322.
- Borghi L, Schianchi T, Meschi T, et al: Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002;346:77-84.
- Choi HK, Atkinson K, Karlson EW, et al: Purine-rich foods, dairy products, and protein intake, and the risk of gout in men. N Engl J Med 2004;350:1093-1103.
- Seltzer MA, Low RK, McDonald M, et al: Dietary manipulation with lemonade to treat hypocitraturic calcium nephrolithiasis. J Urol 1996;156:907-909.
- Parsons JK, Hergan LA, Sakamoto, and Lakin C: Efficacy of alpha-blockers for the treatment of ureteral stones. J Urol 2007;177:983-987.
- Porpiglia F, Vaccino D, Billia M, et al: Coricosteroids and tamsulosin in the medical expulsive therapy for symptomatic distal ureter stones: single drug or association?. Eur Urol 2006;50:339-344.
- Wen CC, Nakada SY: Treatment selection and outcomes: Renal calculi. Urol Clin N Am 2007;34:409-419.
- Limb J, Bellman GC: Tubeless percutaneous renal surgery: review of first 112 patients. Urology 2001;58:345-350.