Kidney stones are poorly soluble constituents, which are part of the urine, which precipitate there forming crystalline clusters of variable size. Their presence can damage the urinary tract and obstruct the normal flow of urine, resulting in a definite clinical picture kidney stones or urolithiasis.
Origin, composition, classification, incidence of kidney stones
To date, the incidence of kidney stones in Italy is 300 per 10 thousand inhabitants (3%). But what leads to such a widespread pathology? To understand this, it is important to clarify how these "pebbles" are formed in our urinary tract and what risk factors affect their formation.
The kidney is the main "purifier" of our body: its goal, in addition to maintaining proper hydration by regulating the elimination of water, is to regulate the concentration of elements important for the correct functioning of the body (mineral salts such as sodium, which we take with salt, or football, important for the bones and many other functions) and eliminate all that is in excess (residues of metabolism, drugs, etc.). The kidney performs these functions by producing urine: it will therefore be composed of water, calcium, potassium, residues and other substances.
Many factors can affect the kidney and therefore the composition of the urine, leading in this case to the formation of stones. They arise from constituents which, present at high concentrations and in some conditions, aggregate and fall in the urinary tract. The urinary tract begins with i kidney calyxes and the pelvis, a funnel-like structure that receives urine produced by the kidney, and they continue with the ureter, a "tube" about a foot long that connects the renal pelvis to the bladder, the real "reservoir" of urine.
Let's clarify what precipitation is with an example: imagine pouring a lot of sugar into a cup of coffee and then stirring. If there is too much sugar, we will find it on the bottom of the cup since, in proportion to the amount of coffee, it was in excessive doses to be dissolved. The excess of the substance (in this case, sugar) that will not be dissolved is the precipitate.
Like sugar in coffee, many substances are also dissolved in urine: some of them, if in excess, form precipitates that can be small, such as crystals urinary, or have larger dimensions and be real stones.
What is the fate of the calculations? Some are large and properties and hardly travel along the urinary tract; others are furniture and for this they cause the typical symptom of calculosis, that is renal colic.
The calculations consist of:
- Calcium salts: Make up the 70% of the calculations. I'm radiopaque, that is easily visible with conventional radiological examinations.
In particular we remember:
- Calcium oxalate (a salt formed by calcium and oxalic acid);
- Calcium phosphate (calcium is associated with phosphate and precipitates with it);
- Struvite (a substance composed of phosphate, magnesium and ammonium, a derivative of ammonia): they are more frequent in women and are diagnosed late, when they have reached an important size. They are rarely mobile and are often associated with urinary tract infections.
- Uric acid: a waste product of our metabolism. Uric acid stones are also called renella and are more common in males. They are typically as small as grains of sand and are often expelled without warning symptoms; however if they exceed 5mm they can obstruct the ureters. Not being visible on x-ray, they are defined radiolucent.
- Cystine: derives from the catabolism of cysteine, an amino acid. It is found in the urine in patients with impaired metabolism or cysteine absorption.
Causes of kidney stones
The formation of stones depends on some conditions. Some factors which favor stones because they cause an imbalance in the body that the kidney tries to correct by eliminating higher quantities of these substances.
• Increased urinary excretion of calcium. It may be due to:
– Hypercalciuria idiopathic: an increase in calcium eliminated by the kidney for reasons that are not better determined;
– Distal tubular acidosis, a kidney disease that causes the kidney to eliminate more calcium;
– Hyperparathyroidism: endocrine disease causing a noticeable increase in calcium in the blood (consequently the amount of calcium filtered by the kidney will increase);
– SupplyAn example is the excessive intake of milk, rich in calcium, due to gastric ulcer. In normal subjects this does not lead to a greater elimination, but in predisposed subjects (for example, patients with idiopathic hypercalciuria) this factor can further accelerate the formation of stones.
• Increased excretion of oxalic acid: for genetic causes, intestinal malabsorption or excessive intake;
• Increased excretion of uric acid: this happens if it is present in high quantities, for example in gout or due to some drugs;
Other factors, however, are not strictly dependent on renal excretion. Among them we remember:
- Chronic urinary obstruction: an obstruction of the urinary tract causes a stagnation of urine, which accumulates upstream of the obstruction. The accumulation facilitates precipitation phenomena.
- Urinary tract infections: in particular, the bacterium Proteus Mirabilis alters the urinary pH, making it less acidic, and raises the levels of ammonium, which is one of the constituents of struvite.
An increase in the aforementioned substances leads to stones due to two mechanisms:
• Supersaturation of some constituents of urine. There solubility of the constituents of the calculations depends on a fine chemical balance that can be altered by:
– Increased their concentration (which depends on the amount of these substances as well as the amount of urine in which they are dissolved)
– Increase in urinary crystals (usually present in small quantities);
– pH: its increase facilitates the formation of struvite and calcium stones; its reduction instead the formation of gravel.
• Alterations in urine composition favoring the precipitation of crystals: Normally in the urine there are substances that prevent the crystals from precipitating. A defect of these inhibitors facilitates their deposition, which in turn will trigger the precipitation of the dissolved elements until the formation of stones. Examples of inhibitors are the citrate, the Tamm-Horsfall protein and the inorganic pyrophosphate.
Risk factors for kidney stones
Some factors, although not directly causing stones, can predispose to its onset. Among them we recognize:
• Genetic causes;
• Age (the incidence increases between 35-40 years and 45-50 years);
• Reduced water intake (dehydration leads the kidney to reabsorb more water and produce more concentrated urine);
• Diet: excessive intake of calcium, animal proteins, fructose, oxalate, etc.
Symptoms of kidney stones
Smaller stones are eliminated asymptomatically; however, the presence of larger stones causes typical clinical manifestations of renal colic Which:
- Ache: the particular pain due to the obstruction of a kidney stone is called colic. Originates in lumbar, Yes radiates to the groin and it has a typical trend: it increases to a peak and then decreases, and then recurs (in medicine it is defined ache sinusoidal). The cause is the dilation upstream of the obstruction, which is followed by an attempt by the musculature to "push" the stone forward to eliminate it; muscle spasms stimulate painful nerve fibers. Often the renal colic are improperly defined as "kidney pain“, “kidney pain" or "kidney pain". In some sub-acute phases it is confused with backache of osteo-muscular origin or with gastritic or intestinal pain.
- Pollakiuria: or the increase in the frequency with which you go to urinate;
- Stranguria: the patient urinates with difficulty because he feels a strong burning;
- Hematuria: presence of blood in the urine. It is rarely visible to the "eye" (urine would be red), but more often only under the microscope;
- Lack of analgesic position, which is the position that a patient with severe pain seeks for relief. In case of colic, the patient fails to do so.
- Neurovegetative symptoms: during colic some nerve pathways are stimulated which cause:
- He retched
- Hydronephrosis: sometimes the stone, obstructing the exit of urine, causes its increase upstream of the obstruction. Most often this happens at the level of the ureter, which can dilate. The continued accumulation of urine over the long term involves the kidney which, like a sponge, swells and becomes enlarged.
Diagnosis of Nephrolithiasis
The first step is careful clinical evaluation symptoms (if any) accompanied by laboratory tests is instrumental.
• Laboratory tests allow to investigate any anomalies that could cause stones and its relapses.
- PTH dosage in 24 hours and vitamin D;
- Calcemia, uricaemia, phosphatemia, azotemia;
- Creatinine and electrolytes for kidney function;
- Dosage of calcium, uric acid, cystine and phosphates;
- Microscopic examination of the sediment will reveal crystals and hematuria;
• Renal ultrasound: it gives general indications on the presence of stones regardless of their composition, however it does not identify those that are too small.
• The direct radiography allows you to locate only the calculations radiopaque (of oxalate and calcium phosphate).
• Urography: it is not performed often as it could exacerbate the patient's pain, already in the midst of renal colic; however, it is effective in finding calculations radiolucent.
• CT scan: useful for identifying dilations of the urinary tract and localizing stones.
Therapy and natural remedies
What to do if kidney stones are found? Exist care for kidney stones? There care main for kidney stones is actually the prevention, as with most medical conditions.
What to eat:
Correcting some eating habits is an important help against kidney stones. Here are some tips:
- Take more citric acid, of which lemon juice is rich;
- Drink more water (2-3 L per day) to produce more urine and facilitate the expulsion of stones;
- Some herbal teas (based on fennel, dandelion, licorice and many others) help diuresis and prevention, however they should be taken with care in case of heart or kidney problems and are not a definitive therapy.
Foods to avoid
Here it is instead what not to eat:
- Foods rich in animal proteins, namely red meats;
- Foods rich in oxalate (spinach, beets, green tea ...);
- Foods rich in calcium and sodium;
- Excess of cola-based drinks, rich in phosphates.
- Seafood, anchovies, caviar and all foods containing uric acid.
- Disinfectants of the urinary tract in case of infections;
- Acidifying drugs or alkalizing urine (based on what alteration in pH caused the formation of the stone);
- NSAIDs and other pain relievers they are often used to relieve the patient's pain; for nausea and vomiting they are sometimes prescribed antiemetics.
- THE diuretics they are especially useful for calcium calculations.
There surgical therapy aims to shatter the stone after having localized it through a catheter inserted inside the ureter, with techniques called ureteroscopic endoscopic lithotripsy, in case the catheter is inserted starting from the urethra and then made up through the bladder and ureter, or percutaneous nephrolithotomy, if the ureter is reached by pricking the wall of the abdomen. Often these two techniques can be combined, especially in case of lithiasis of the renal pelvis. In other cases, the urologist surgeon can directly remove the stone throughpyelotomy or nephrotomy (i.e. the surgical incision of the renal pelvis or the kidney itself).
Transcutaneous or percutaneous lithotripsy
This recent technique allows calculations to be broken up by “bombarding” them with a series of short shock waves transmitted by the water in a tank in which the patient is immersed. This makes it easier to expel the crushed stones in the urine.
Kidney stones in pregnancy
Kidney stones in pregnancy is an event not to be underestimated. In fact, some treatments such as extracorporeal lithotripsy or percutaneous nephrolithotomy cannot be performed due to the possible damage that the fetus could have. Therapy is therefore carefully considered by specialists, and can be medical, and therefore conservative, or surgical.Tags: Urinary system Nephrology Urology