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Stones of the urinary tract (kidney, ureters
and bladder) are a very common condition affecting up to 12% of the US
population. Stones occur in both men and women of all ages; however, they
most commonly occur in Caucasian males between 45 and 55 years. Children may
also get kidney stones but it is not common.
Anatomy
- The
kidneys are a pair of bean shaped reddish-brown organs that lie on
either side of the spinal column and just below the diaphragm. They are
about 5 inches (12.5 cm.) long and 3 inches (7.5 cm.) wide (Figures 1and
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- Urine
is produced in the kidneys and travels down through the ureters to
enter the bladder
- On
the medial (facing the spine) border the kidney is notched at the
hilus, the point where the major artery to the kidney enters and vein
leaves
- The
ureter also leaves from the hilus
- The
kidney is made up of over a million renal tubules (nephrons). All the
nephrons together form the cortex. The nephrons filter the blood of
waste products that pass into the urine
- The
urine passes from the nephrons into collecting tubes called calyxes and
then into the renal pelvis (the dilated upper portion of the ureter)
and into the ureter, which conducts the urine into the urinary bladder
- A
capsule of thin tissue encloses each kidney
- The
bladder is located in the pelvis. It is held in place by ligaments and
can be felt in the lower abdomen when full
- The
urinary bladder is a hollow muscular organ that serves as a reservoir of
urine. Normally the bladder can hold 250 - 450 cc (8 - 15 ounces) of
urine
- The
urethra is located at the base (lowest part) of the bladder and drains
the urine out of the bladder. In women the outlet of the urethra can be
seen just in front of the vagina. In men the urethra lies within the
penis
- In
males, the bladder has the prostate gland below (through which the
urethra passes). In females, the uterus and the vagina lie behind the
bladder
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Figure 1 - Anatomy of the kidney. The upper
portion of the kidney is cut away to expose the cortex, calyxes and renal
pelvis. The renal artery and ureter enter and the renal vein leaves the
kidney at the hilus. The adrenal gland rests on the upper pole of the
kidney. © N. Gordon
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Figure 2 - On the left side are seen the
kidney and adrenal glands along with the ureter extending from the kidney
to the bladder. On the right side are seen a staghorn stone in the kidney
pelvis as well as stones in the ureter, bladder and urethra.© C. McKee
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Pathology
- Stone
formation in the urinary tract occurs due to the precipitation
(particles coming out of a solution) of substances in the urine in the
following situations:
- Increased
concentration of the urine due to dehydration may lead to precipitation
of stones
- Alkaline
urine predisposes to some stones while an acid urine leads to other
types of stones
- The
presence of a foreign body like bacteria, blood or pus in the urine may
cause crystallization of minerals around these bodies
- Abnormal
mineral/substance content of the urine - increased excretion of
calcium, uric acid, oxalate, etc., can cause these to deposit as stones
- Conditions
that may lead to urinary stone formation include:
- Increase
in calcium. Some of the conditions that increase urine calcium are
hormonal abnormalities (hyperparathyroidism, Cushing's disease,
hyperthyroidism), Vitamin D toxicity, increased calcium intake,
prolonged bed rest (as with paralysis) and tumors such as multiple
myeloma and metastatic cancer to bone
- Increase
in oxalate. Some of the conditions that increase urine oxalate are an
increase in oxalate intake, short gut syndrome (patients who have had
considerable length of their bowel removed for Crohn's disease, morbid
obesity or trauma) and excess Vitamin C
- Increase
in uric acid. Some of the conditions that increase urine uric acid are
certain tumors like leukemias and lymphomas, side effects of drugs like
aspirin and some sulfa drugs and certain metabolic conditions such as
gout
- High
cystine levels in the urine are seen in an inherited condition called
cystinuria, which causes cystine stone formation.
- Stones
occur more in hot weather as loss of water through sweat concentrates
the urine inducing stone formation
- Composition
of urinary stones:
- Calcium
oxalate with or without calcium phosphate - 75%
- Calcium
phosphate only - 7%
- Magnesium
ammonium phosphate - 12%
- Uric
acid - 7%
- Cystine
- 2%
- The
most common locations for deposition of stones are in the areas of
narrowing of the urinary tract (Figure 2):
- Junction
of the kidney and ureter (the ureteropelvic junction)
- At
mid ureter where it crosses over the iliac bone to enter into the
pelvis or where the ureter crosses over the iliac blood vessels
- Junction
of the ureter and bladder
- In
women, where the ureter passes under the uterine artery
History and Examination
- Symptoms
of urinary stones may vary according to the location of the stone
- Renal
colic (pain) is the predominant symptom of urinary stone disease. This
pain is caused by spasm of the ureter and distension of the ureter and
capsule of the kidney above the stone. The pain may start in the flank
and radiate down to the bladder and genitalia. The pain is usually
intermittent and can be excruciating and associated with nausea and
vomiting. These symptoms have to be differentiated from gallbladder
disease, appendicitis, pancreatitis and intestinal obstruction
- Blood
in their urine (hematuria). The urine is usually blood tinged, but the
bleeding can be significant. Occasionally, no blood may be found in the
urine
- Signs
and symptoms of a urinary tract infection (UTI) with urinary urgency,
frequency, fever and painful urination (dysuria). Urinary obstruction by
stones can predispose to frequent UTIs
- Long
standing stones may cause partial obstruction of the ureters at the
ureteropelvic junction and can lead to swelling of the kidneys
(hydronephrosis) with a constant dull ache in the flank. Long standing
hydronephrosis can lead to kidney failure
Diagnostic studies
- Tests
to evaluate for an infection:
- Blood
white cell count (WBC) may be raised
- Urine
analysis may show evidence of blood, pus or stone crystals
- Urine
culture for bacteria
- Urine
for Increased or decreased acid content
- Determination
of blood or urine levels of calcium, proteins, phosphorus, oxalate, uric
acid or cystine in cases of patients with known recurrent stones is
carried out to identify the possible conditions causing stone formation.
In most cases no specific cause is found
- X-ray
of the abdomen may show a stone and its location. About 90% of stones
with calcium can be seen on X-ray. Cystine and uric acid stones usually
are not seen
- Intravenous
pyelogram (IVP). Contrast (X-ray dye) is injected into a vein and passed
into the urine by the kidneys. Serial X-rays of the abdomen are obtained
to see the kidney and ureters. Significant findings include delay in
seeing the affected kidney (due to possible decreased kidney function),
evidence of swelling of the kidney and ureter (hydronephrosis and
hydroureter) and location of the stone
- Ultrasound
of the abdomen may be done without contrast and may locate stones
- Computerized
tomography scan (CT scan) may be used to locate and determine the size
of a stone (Figure 3)
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Figure 3 - CT scan of the abdomen showing
both kidneys and small calcified stones (arrowheads). Courtesy L. Ashker,
DO
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Acute care
- About
90% of stones will pass spontaneously. Patients are given increased
fluids to flush out the stone and pain medication. Fluid intake is
increased to about 3 liters (quarts) per day to maintain a urine output
of about 2 liters a day
- Stones
less than 4 mm (1/8 inch) in size almost always pass through. Stones
above 6 mm have less than a 10% chanced of passing
- Patients
are advised to strain their urine to watch for passed stones. The stone
may take several days before it passes. Stones are usually examined for
chemical content
Indications for surgery
- Large
stones. In long standing UTI, very large stones that may fill the entire
kidney pelvis may develop. These are sometimes known as
"staghorn" calculi (stones)
- Complete
obstruction of the urinary system by a stone
- Demonstrated
poor renal function
- Evidence
of serious urinary tract infection such as a kidney abscess
- Stones
in high risk patients (e.g., airplane pilots) or in transplant patients
who cannot tolerate infection
- A
stone in a patient with only one kidney
Surgical procedures
- Surgical
therapy for urinary stones has seen new advances in the past decade with
the introduction of laser and ultrasound
- Treatment
of urinary stones is determined by the size, location, and composition
of the stone; anatomy of the urinary system and function of the kidney
- Small
stones (less than 2 cm):
- Stenting
the ureter - Small stones which take longer to pass than expected or
are causing symptoms may be managed inserting a long plastic tube into
the ureter on the side of the stone. The stent (tube) acts to keep the
ureter open and urine flowing, so that there is no loss of renal
function or infection. The stent is inserted by first placing a
cystoscope into the bladder. The cystoscope is a lighted instrument
with a lens system at the end within the bladder and an eyepiece at the
other end for viewing. The stent is positioned in the ureter through a
separate 'working' channel in the cystoscope and dilates the ureter
- Shock
Wave Lithotripsy (SWL) - This treatment is effective for smaller
stones. Shock waves are transmitted through the skin and muscles until
they reach the stoned that have a different density. The sound waves then
cause fragmentation of the stones. It is noninvasive and has a low risk
for complications. The need for anesthesia depends on the intensity of
shock waves needed. The shock waves are timed with an EKG to prevent
any abnormal heart rhythms. SWL may not be effective in obese patients.
Cystine stones are also resistant to SWL therapy. SWL is usually not
effective in breaking up of large stones. (Figure 4)
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Figure 4 - Breaking up a kidney stone using
Shock Wave Lithotripsy. The stone is centered in the machine following
which the stone is broken up with soundwaves. © C. McKee
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- Larger
stones (over 2 cm) (Figure 5)
- Percutaneous
NephroLithotomy (PNL) - This procedure is usually done under anesthesia
and with X-ray guidance. A tract is made from the skin into the pelvis
of the kidney. A balloon catheter about 10 mm in diameter is used to
form this tract. Hollow dilators are passed along the tract from skin
to kidney. Once the tract is formed, a flexible scope is inserted into
the kidney to visualize the stone(s). The stone may be extracted
through this tract or may be broken up by ultrasonic lithotripsy (UL),
electrohydraulic lithotripsy (EHL), laser lithotripsy or pneumatic
(air) lithotripsy (lithotripsy, breaking up of a stone). The fragmented
stones are then removed through the tract. The tract usually closes
spontaneously once the dilator is removed with minimal scarring. PNL is
successful in 70-100% of cases. Smaller retained fragments in the
urinary system may pass spontaneously or may require additional SWL
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Figure 5a - Urinary stone in a ureter as
seen through an ureteroscope. Courtesy D. Harold, MD
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Figure 5b - Stone is broken up into smaller
fragments before removal. Courtesy D. Harold, MD
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- Ureterorenoscopy
(ureteroscope)- A delicate fiberoptic scope is inserted through the
bladder into the ureter to the kidney. The stone(s) are seen and using
ultrasonic, electrohydraulic, laser or pneumatic lithotripsy are broken
down. Smaller stones may be pulled out using thin grasping instruments
or a fine wire basket. (Figure 6) This procedure is about 90%
successful. Once again, smaller retained stones may need an additional
SWL
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Figure 6 - Urinary stones may be removed
using a grasping forceps or wire basket, or broken up using the
electrohydraulic and laser lithotriptors. © C. McKee
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- Ultrasonic
lithotripsy (UL) - Sound waves, vibrating at about 25000 times a
second, are passed down a probe to the tip. The tip causes
fragmentation of stones upon contact. The probe is passed though the
tract from a PNL or ureteroscope (see above) to reach the stone.
- Electrohydraulic
lithotripsy (EHL) - An electrical discharge is passed down an insulated
probe to create a spark at its tip. The heat of the spark creates a
shock wave, which is transmitted to the stone on contact. About 50-100
sparks are discharged per second. EHL is very effective for hard
stones.
- Laser
lithotripsy (LL) - laser is passed down a flexible probe through a PNL
tract or ureteroscope to break up the stones
- Pneumatic
lithotripsy (PL) - Compressed air pushes a metal projectile against the
head of a probe at a frequency of 15 times a second. This causes
fragmentation of the stones on contact with the probe.
- Staghorn
calculi
- Staghorn calculi are so
named because these extremely large stones fill up the entire
collecting system of the kidney (pelvis and calyses) with branching
resembling the horns of a stag. These stones are almost always caused
by infection of the urine
- SWL or PNL may be used to
break up these stones. If there is extreme dilation of the collecting
system or multiple branching of the stone, open nephrolithotomy may be
necessary
- Open nephrolithotomy - This procedure is done under
general anesthesia. The patient is usually placed on the side opposite
the affected kidney. An incision is made on the side at the lower ribs.
The muscles of the back are divided to reach the kidney. The pelvis of
the kidney is opened, and the stone removed. The pelvis of the kidney is
closed as well as the muscles and skin. A drain may be left in
place.(Figure 7)
- Lower
tract stones. Stones in the lower ureter, bladder or urethra are usually
managed by cystoscopy or ureterorenoscopy with one of the methods
mentioned above
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Figure 7 - Nephrolithotomy with direct
surgical removal of a kidney stone. © C. McKee
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Complications
- SWL
has a very low incidence of complications. Bleeding into or around the
kidney, scarring of the kidney or later development of hypertension has
been reported
- Percutaneous
nephrostolithotomy (PNL) can cause bleeding, infection, urinary leak or
damage to abdominal organs, which may require surgery. Retained stones
may cause symptoms again. Use of contact lithotripsy (UL, EHL, LL or PL)
may be associated with damage to the ureters.
- Ureteroscopy
may cause ureter damage that may require open surgical repair.
- Open
nephrolithotomy may cause respiratory complications such as atelectasis
(unexpanded lung near the diaphragm), pneumonia, chronic pain from
damage to the ribs and the nerves that run along the ribs, bleeding and
infection
After care
- Minimally
invasive techniques like SWL, PNL or ureterorenoscopy have minimal
recovery times. Patients usually require minimal pain medication and are
usually discharged the same day
- Hematuria
(blood in urine) is usually seen after such procedures and usually
resolves in a few days
- Open
nephrolithotomy usually requires a few days of admission. Patients will
require breathing exercises to prevent respiratory complications. Drains
may be removed in a few day
- If
a cause for stone formation is discovered, this should be treated to
prevent formation of other stones. Diet modifications, which include
avoiding dairy and meat products may reduce calcium levels. Drugs may be
prescribed to reduce calcium or uric acid levels
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