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Urinary Stones
Removal

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 2 )
    1. Urine is produced in the kidneys and travels down through the ureters to enter the bladder
    2. 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
    3. The ureter also leaves from the hilus
    4. 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
    5. 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
    6. A capsule of thin tissue encloses each kidney
    7. 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
    1. 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
    2. 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
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 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

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:
    1. Increased concentration of the urine due to dehydration may lead to precipitation of stones
    2. Alkaline urine predisposes to some stones while an acid urine leads to other types of stones
    3. The presence of a foreign body like bacteria, blood or pus in the urine may cause crystallization of minerals around these bodies
    4. 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:
    1. 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
    2. 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
    3. 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
    4. High cystine levels in the urine are seen in an inherited condition called cystinuria, which causes cystine stone formation.
    5. Stones occur more in hot weather as loss of water through sweat concentrates the urine inducing stone formation
  • Composition of urinary stones:
    1. Calcium oxalate with or without calcium phosphate - 75%
    2. Calcium phosphate only - 7%
    3. Magnesium ammonium phosphate - 12%
    4. Uric acid - 7%
    5. Cystine - 2%
  • The most common locations for deposition of stones are in the areas of narrowing of the urinary tract (Figure 2):
    1. Junction of the kidney and ureter (the ureteropelvic junction)
    2. 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
    3. Junction of the ureter and bladder
    4. 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:
    1. Blood white cell count (WBC) may be raised
    2. Urine analysis may show evidence of blood, pus or stone crystals
    3. Urine culture for bacteria
    4. 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)
Figure 3 - CT scan of the abdomen showing both kidneys and small calcified stones (arrowheads). Courtesy L. Ashker, DO

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):
    1. 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
    2. 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)
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
  • Larger stones (over 2 cm) (Figure 5)
    1. 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
Figure 5a - Urinary stone in a ureter as seen through an ureteroscope. Courtesy D. Harold, MDFigure 5b - Stone is broken up into smaller fragments before removal. Courtesy D. Harold, MD
    1. 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
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
    1. 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.
    2. 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.
    3. Laser lithotripsy (LL) - laser is passed down a flexible probe through a PNL tract or ureteroscope to break up the stones
    4. 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
    1. 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
    2. 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
    3. 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
Figure 7 - Nephrolithotomy with direct surgical removal of a kidney stone. © C. McKee

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