Kidney Stones
Kidney stones (calculi) are hardened mineral deposits that form in the kidney. They originate as microscopic particles and develop into stones over time. The medical term for this condition is nephrolithiasis, or renal stone disease.
The kidneys filter waste products from the blood and add them to the urine that the kidneys produce. When waste materials in the urine do not dissolve completely, crystals and kidney stones are likely to form.
Small stones can cause some discomfort as they pass out of the body. Regardless of size, stones may pass out of the kidney, become lodged in the tube that carries urine from the kidney to the bladder (ureter), and cause severe pain that begins in the lower back and radiates to the side or groin. A lodged stone can block the flow of urine, causing pressure to build in the affected ureter and kidney. Increased pressure results in stretching and spasm, which cause severe pain.
Signs and Symptoms
Small, smooth kidney stones may remain in the kidney or pass without causing pain (called "silent" stones). Stones that lodge in the tube that carries urine from the kidneys to the bladder (ureter) cause the urinary system to spasm and produce pain. The pain is unrelated to the size of the stone and often radiates from the lower back to the side or groin.
A "small" stone (usually 4 mm in diameter or less) has a 90% chance of spontaneous passage. Stones that are 8 mm in diameter or larger usually require medical intervention.
Other symptoms of kidney stones may include the following:
- Blood in the urine (hematuria)
- Increased frequency of urination
- Nausea and vomiting
- Pain during urination (stinging, burning)
- Tenderness in the abdomen and kidney region
- Urinary tract infection (fever, chills, loss of appetite)
Diagnosis
Diagnosis of renal stone disease involves a medical history, physical examination, laboratory evaluation, and imaging tests. The physician determines if the patient has a history of kidney stones, documents past medical conditions, and evaluates present symptoms. Physical examination may be difficult if the patient is experiencing severe pain and is unable to remain still. Lightly tapping on the kidney region often worsens the pain. Fever may indicate a urinary tract infection that requires antibiotics.
Laboratory tests include urinalysis to detect the presence of blood (hematuria) and bacteria (bacteriuria) in the urine. Other tests include blood tests for creatinine (to evaluate kidney function), BUN and electrolytes (to detect dehydration), calcium (to detect hyperparathyroidism), and a complete blood count (CBC; to detect infection).
Imaging tests
Imaging tests used to diagnose kidney stones include ultrasound, intravenous pyelogram (IVP), retrograde pyelogram, and computed tomography (CT) scan.
Ultrasound
This test uses high-frequency sound waves to produce pictures of internal structures (e.g., organs, kidney stones). Ultrasound can detect a dilated (stretched) upper urinary tract and kidney caused by a stone lodged in the ureter, but usually cannot detect small stones, especially those located outside the kidney. It is the preferred imaging method for kidney stone patients who are pregnant.
Intravenous Pyelogram (IVP)
This test involves taking a series of x-rays after injecting a contrast agent (dye) into a vein. The contrast agent flows through the veins, is excreted by the kidneys, and improves the x-ray images of the kidneys and ureters. If a kidney stone is blocking a ureter, the contrast agent builds up in the affected kidney and is excreted more slowly. Most kidney stones (e.g., calcium stones) can be precisely located using this procedure. There is a slight risk for an allergic reaction to the contrast agent during this procedure and overall kidney function must be normal. IVP can take a very long time if the blockage to the kidney is severe.
Retrograde Pyelogram
A cystoscopy (i.e., a procedure in which a telescopic instrument is inserted into the urethra) is performed to locate the opening from the ureter to the bladder. The contrast agent is injected directly into this opening and an x-ray is taken to locate the kidney stone.
This procedure eliminates the risk for an allergic reaction to the contrast agent because the dye does not reach the bloodstream, but it may require anesthesia. While retrograde pyelogram is the most reliable method for visualizing the urinary system and detecting stones, it is generally used only when other imaging methods are inadequate or unsuccessful.
Computerized tomography (CT Scan)
This test uses a scanner and a computer to create images of the urinary system. It is performed quickly but may have difficulty detecting small stones located near the bladder. CT scan can also help identify medical conditions (e.g., ruptured appendix, bowel obstruction) that cause symptoms similar to kidney stones.
Newer scanners do not require a contrast agent. The non-contrast CT scan is the most common imaging test used to evaluate a possible kidney stone attack. If any stones are found, a plain abdominal x-ray is also taken to determine their size, shape, and orientation. X-rays are used for follow-up studies to monitor the stones' progress.
Stone Formation
Kidney stones form when there is a high level of calcium (hypercalciuria), oxalate (hyperoxaluria), or uric acid (hyperuricosuria) in the urine; a lack of citrate in the urine; or insufficient water in the kidneys to dissolve waste products. The kidneys must maintain an adequate amount of water in the body to remove waste products. If dehydration occurs, high levels of substances that do not dissolve completely (e.g., calcium, oxalate, uric acid) may form crystals that slowly build up into kidney stones.
Urine normally contains chemicals—citrate, magnesium, pyrophosphate—that prevent the formation of crystals. Low levels of these inhibitors can contribute to the formation of kidney stones. Of these, citrate is thought to be the most important.
Treatment
Once the stone's location, size, shape, and composition have been established, and other medical complications, such as infection, have been identified, the course of treatment is determined.
The size of the stone is a major factor in determining treatment. Most kidney stones are less than 4 mm wide (about 3/16 of an inch) and pass without medical intervention.
There are a number of ways to remove Kidney stones. Again, size is usually the determining factor in which treatment will be used. These treatments include: Ureteroscopy, Lithotripsy, Laser Lithotripsy, Ultrasonic Lithotripsy, Electrohydraulic Lithotripsy (EHL), Extracorporeal Shock Wave Lithotripsy (ESWL), Percutaneous Nephrolithotomy, Chemolysis, Open Nephrolithotomy and Partial Nephrectomy.
Laser and Lithotripsy
Lithotripsy
A variety of nonsurgical techniques have been developed to crush or pulverize kidney stones. Lithotripsy uses a machine called a lithotripter to project shock waves or sonic pulses against the stone and break it into tiny particles that can pass naturally in the patient’s urine. This can be done in several ways, depending on the size and location of the stone.
Patients undergoing lithotripsy are given a sedative and a general or local anesthetic. Shock waves are focused on the kidney stone at a rate of approximately one per second and the therapy may last over an hour. Bruising may result from the shock waves and discomfort may be experienced as the crushed calculi are passed; but, most patients resume normal activity in a few days.
Lithotripsy is highly effective for stones in the kidney and upper ureter. More than one treatment may be required. Rarely, a catheter may be inserted through a small incision in the back to drain the kidney and remove the stone fragments. Patients with very large stones or complicating medical conditions may require different treatment.
Ultrasonic Lithotripsy
Ultrasonic lithotripsy locates the stone using an optical scope and electronic probe, inserted into the ureter under epidural (spinal) anesthesia. High frequency ultrasound waves are directed at the stone and break it up. The fragments can be passed naturally by the patient or removed by forceps, basket extraction, or suction through the scope instrument. Ultrasonic lithotripsy can only be employed when there is a straight path to the stone.
Electrohydraulic Lithotripsy (EHL)
This technique uses a probe to break small stones with shock waves generated by electricity. The physician positions the tip of the probe 1 mm from the stone through a flexible ureteroscope and projects electrically generated hydraulic shock waves at the stone. These fragments can be passed by the patient or removed by extraction methods. EHL requires general anesthesia and is generally not used in close proximity to the kidney because the shock waves can cause tissue damage. Fragments tend to scatter widely, making retrieval or extraction difficult.Extracorporeal Shock Wave Lithotripsy (ESWL)
Extracorporeal shock wave lithotripsy uses highly focused impulses projected from outside the body to pulverize kidney stones.
The patient is positioned on a cushion atop a table and may be given a sedative. Lithotripters are effective at crushing cystine stones and those in the lower ureter. The stone usually is reduced to granules that can be passed in the patient's urine.
Very large stones, those 3 centimeters (about one inch) or more in diameter, may require several ESWL treatments to break up completely or may produce such a large volume of fragments that they block the ureter. This condition is called "steinstrasse," (a German word meaning "street of stone")
Large struvite stones, because of their jagged shape, sometimes become lodged in positions or locations that make them difficult to treat effectively with shock waves.
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