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Stones that form and accumulate in the kidneys are referred to as kidney stones. If they move into the ureter they are called ureteral stones. Kidney stones and ureteral stones form (nephrolithiasis) through the crystallization in supersaturated urine of "physiological" substances such as calcium, magnesium, phosphate, oxalate and uric acid. In the slow course of their growth they can entirely fill portions of a kidney and thus lead to functional impairment. Men are generally more affected by nephrolithiasis than women.


Kidney stones often do not cause symptoms and are only detected through targeted examination methods (e.g. ultrasound). The size, shape and position of the stone (also: concretion) are critical factors for nephrolithiasis symptoms. Small stones and granules can be flushed out of the body through increased fluid intake, without active medical intervention.

A pulling or pressing feeling in the flank area or hematuria (blood in the urine) are often an indication of kidney stones.

If kidney stones detach and enter the narrow portions of the ureter, they can get stuck there and - depending on their size - trigger renal colic via the resulting urinary obstruction. This can result in stabbing or dull pains in the kidney area or back, often accompanied by nausea, vomiting, and occasionally also fever. Sometimes blood is visible in the urine (hematuria). Renal colic pain is one of the most severe pains there is, therefore these colics require immediate medicinal or even urological-surgical treatment (see below).

Causes and Risks

Kidney stones are formed from the constituents of urine. Their development depends on many factors, e.g. dehydration, drinking habits, diet and physical inactivity. Those substances that are not dissolved in the urine, accumulate and crystallize into stones of different sizes and shapes. The reduction in function of the pyelocaliceal system (disturbed or delayed urine outflow) triggered by the stones often contributes to bacterial colonization, which in turn can lead to urinary tract infections. In extreme cases it can cause suppuration of the kidney (abscess formation) or even blood poisoning (urosepsis) with symptoms of urinary infection, high fever and chills, severe malaise, up to complete circulatory collapse. The possible urinary obstruction associated with this can lead over a prolonged period to damage of the affected kidney. If urinary obstruction exists on both sides, or diminished kidney function is already present, there is even a long-term threat of kidney failure (uremia).

Examination and Diagnosis

If kidney stones are suspected, a medical history interview and physical examination will usually be followed by blood and urine tests. Within the scope of the blood tests, levels of creatinine, potassium, phosphate, urea and uric acid will be determined in order to detect infections and analyze renal function. Examining the urine may verify traces of blood (hematuria). For further diagnosis of the kidneys and urinary tract - e.g. location and size of stones, readings on kidney discharge, evidence of urinary obstruction - other methods may be used such as ultrasound, computed tomography (CT) or X-ray contrast imaging (either as an intravenous pyelogram where the contrast medium is injected into a vein and excreted by the kidneys, or a retrograde pyelogram where the contrast agent is injected into the ureter from below through a fine plastic tube in the course of endoscopic bladder imaging).


Small kidney stones can flush out in the urine by themselves (spontaneous stone passage). To accomplish this, lots of liquids as well as physical activity are necessary. With kidney stones that consist entirely of uric acid, a medicinal dissolution (chemolitholysis) is possible. For this the patient must, over an extended period, take a drug that alters the pH (acid value) of urine. Uric acid stones can actually dissolve in the alkaline pH range. If this does not result in the spontaneous passage of a stone, it must be actively removed. A range of the most modern methods are available for this. In extracorporeal shock wave lithotripsy (ESWL), ureteral stones are crushed into small particles and can then exit naturally or be removed via further minimally invasive procedures. Percutaneous nephrolithotomy (PNL) enables the removal of large stones: here an endoscope is inserted through a small incision into the pyelocaliceal system, where using a laser probe or pneumatic shock waves the stones can be broken up (lithotripsy). Subsequently, the small stone pieces are flushed out of the kidney. The latest advances in this method allow the use of devices with a diameter of only 4 millimeters in some cases. Through the process of ureterorenoscopy stone removal (URS) it is now possible to enter the ureter or even the pyelocaliceal system with very thin rigid or flexible instruments under direct visual control, then to remove the kidney or ureteral stones surgically under endoscopic control. If the stones are too large for this, they can be crushed beforehand with laser lithotripsy.

In this method a Double-J ureteral stent or catheter is inserted in the ureter a few days before the ureteroscopy, to allow easier entrance to the pre-stretched ureter for the operation. Depending on the intra-operative results and existing residual stones, it may be necessary to leave the stent in for a few days or weeks after surgical stone removal, so that all stone fragments can exit without colic, and no scarring of the ureteral strictures occurs.

Course and Prognosis

If there is already a kidney stone in the medical history, the probability of a recurrence in the future is over 50 percent. This risk can be reduced, however, if the patient significantly increases his or her daily fluid intake and ensures sufficient physical exercise. The formation of stones is thus diminished due to the urine dilution. In this context it is also important to clarify the cause of stone formation. For this purpose a urine-specific metabolic examination is recommended, in which a detailed analysis of urine and blood levels is done. This is mainly needed for rare metabolic diseases such as cystinuria, because for this very special measures are later required.

Miscellaneous/Other Comments

The Department of Urology of the Medical Center - University of Freiburg has an established focus on "Minimally invasive techniques and stone therapy" and offers both modern and long-recognized methods for minimally invasive treatment of all urological organ systems and diseases as well as modern techniques of surgical therapy. Through continuous training of highly qualified doctors and nurses, particularly in the use of new technologies, maximum safety for the patient can be guaranteed.