Urinary stones are crystal aggregates which form and grow in urine. Urinary lithiasis is a very old disease: urinary stones have been found in a 7,000 years old mummy.
The treatment of urinary stones is ancient as well. From the "saxifraga" plant cooked in wine, used in the middle ages, to the modern extracorporeal lithotripsy with shock waves, mankind has been always troubled by urinary lithiasis. Normally, several different substances (often crystals)

are present in urine, in a complex solution. The main hypotheses on urinary stones formation are the following.
Supersaturation.
An excess of concentration above a specific limit leads to crystallization. The saturation threshold is dependent upon temperature and acidity (pH) of the solution. An example of this phenomenon can be observed adding salt to water. Beyond a certain amount, the salt will not dissolve in water anymore. When saturation limit of a substance in urine is exceeded, crystal nucleation and growth will occur. After a meal, an increased concentration of ossalate and calcium may occur in urine. During the night, when fluid intake is low, supersaturation may be reached. It is said that probably urinary stones form at night.  

Inhibitors: Even when high concentration and supersaturation are reached, in some patients crystallization doesn´t  occur. This is due to some natural substances which are present in urine, like some proteins, magnesium and citrate. These substances may interfere with crystallization. In certain patients there is a decreased concentration of these inhibitors of crystallization. Citrate and magnesium administration is used for urinary stones prevention.

Crystal retention Generally crystals are found in urine of healthy people, but only 10% of population will form urinary stones. Anatomic and biochemical factors can contribute to adhesion of small crystals to the urinary mucosa.

Matrix: matrix is an organic amorphous substance (a mucoprotein) which is present in urinary stones in highly variable proportion. Though the role is uncertain, some Authors have postulated that it can be involved in urinary stones formation.

Urinary stones are usually made of several different layers, that at section resemble the look of concentric growth of trees.
Most stones (70-90%) contain calcium, together with oxalate, phosphate, or carbonate. Struvite (magnesium ammonium phosphate) are 15-20% of all stones, and often they are due to urinary infection. Mostly they occur in women. Uric acid stones (5-10%) are related to hyperuricemia; these stones are radiolucent (they are not seen with plan x-rays) and often they can be treated with medical therapy. Cystine stones are rare (around 1%) and usually secondary to a congenital metabolic defect. The incidence of urinary stones is increasing in last decades. Bladder stones incidence, prevalent in the past centuries, is now decreasing in western countries, where an increment of upper urinary tract (kidney and ureters) stones is observed.
The chance of being diagnosed with urinary stones along life is 2.5-10%. About 20% of patients with urinary stones require admission to a hospital. The age at first diagnosis is between 20 and 50 years.  Every patient with at least one episode of urolithiasis should undergo periodic kidney ultrasound, for the high risk of stone recurrence (50% at 10 years).
There is geographic and dietary variety in the incidence of urinary lithiasis in different populations.  Which are risk factors for urinary stones?

*A diet rich with animal proteins and poor of vegetables and fibers, like the ones in western countries

*A high intake of sodium

*Low fluid intake, especially in warm and dry climates (for the risk of excess urinary concentration)

*Contrary to what people believe, a diet rich of calcium may prevent urinary stones.

Several diseases can be associated to an increased risk of stone formation, including some metabolic disorders, like renal tubular acidosis, hyperuricemia, primary hyperoxaluria, cystinuria, medullary sponge kidney. Hyperparathyroidism (hyperfunction of parathyroid glands), sarcoidosis, some tumors, especially of the blood (leukaemia, lymphoma), can all increase the risk of urinary stones.

However, the majority of urinary stones (70%) are calcium stones without apparent aetiology, with normal or increased urinary calcium concentration.
About 15-20% of urinary lithiasis is related to urinary infection, since the bacteria can alter the normal acidity of urine.An increased risk of stone forming is associated to immobilization, urinary tract obstruction, surgical urinary diversion, bowel surgery for obesity, and to some drugs therapy.

Symptoms and diagnosis

Urinary stones can cause different symptoms according to the site. A kidney stone not obstructing the urine flow, can be completely asymptomatic, or produce a mild flank pain.
The colic is due to a stone obstructing the passage of urine, in the kidney or the ureters, with painful overdistension cranial to the stone. In patients with a stone, the risk of having colic is 40-50 %. The colic pain is often very strong, intermittent, in the lumbar area or in the flank. There can be nausea and vomit. When the stone is in the ureters, the pain can irradiate toward the iliac region, to reach the labia or the scrotum. When the stone is in the distal ureter, it can mimic cystitis, with increased urinary frequency and urgency.
Haematuria (blood in the urine) can be present in 40% of cases. If there is a concomitant urinary infection, fever with chills may occur. It is important to remember that sometimes the urinary obstruction by the stone can be partial, and the patient may be asymptomatic. It is mandatory to undergo periodic ultrasound scan of the kidney, after a first episode of urolithiasis.
Usually ultrasound scan of the bladder and kidney is the first approach to urinary stones. Ultrasound scan is not invasive, not painful, performed through a probe on the abdomen. With the exam, the kidney

and the bladder can be visualized. Stones of the kidney, of the very first tract and last tract of the ureter can be diagnosed. The eventual distension (hydronephrosis)

of the kidney, due to obstruction of urine passage, can be easily seen.  However the whole ureter, which is a thin tube passing behind the bowel, is hard to identify by ultrasound.
Plan x-ray of the abdomen can show calcifications on the kidney area, or along the probable way of the ureter. Since more than 80% of stones contain calcium, they may be seen by plan x-ray. Nevertheless, small or along the iliac bone stones can be missed.
In these cases for decades urography has been the main test for urinary stones diagnosis. It is performed through I.V. injection of a contrast medium, containing iodine. Diagnosis of iodine contrast adverse reaction and severe renal failure are contraindications to urography. With urography all excretory way can be seen on a 2 dimension film. Size and site of the stones are diagnosed. Even radiolucent stones (uric acid, struvite, cystine) can be seen as a filling defect in the contrast.
In then last years urography has been gradually replaced by CT scan. Ct scan can be used without contrast medium, providing accurate information about the size and the site of the stone.When contrast medium is used, with last generation CT scan 3D imaging of excretory ways can be obtained.

The aim of medical therapy is to prevent new stones formation and the growth of already present stones. Only in selected case medical therapy can dissolve stones. In patients with pure acid uric stones, calcium free, (easily diagnosed because they are radiolucent), urine alkalization can dissolve even large stones. Urine is usually acid. Modifying the pH (a number which is inversely proportional to the acidity of a solution), acid uric stones can be dissolved in 3-6 months of therapy. The cheapest drug for urine alkalization is sodium carbonate. It is contraindicated in patients with hypertension (for increased intake of sodium). Urine pH should be maintained at 6.5-7, for 3-6 months.
Allopurinol, a drug used to decrease uric acid in blood, can be administered when hyperuricemia is present.
In patients with calcium stones, potassium citrate may decrease the risk of stone recurrence. When hypercalciuria is present, administration of thiazides (a group of diuretics) can be effective for stone prevention. An increased fluid intake is however essential in patients with urinary stones.
Even patients with large kidney stones can be asymptomatic, until the stones obstruct the passage of urine.  Occasionally haematuria or a dull, mild flank pain may occur.
When the first sign of a stone is a renal colic, the treatment should be aimed to relieve acute pain.  Non steroidal anti-inflammatory drugs can be useful, while the role of antispasmodic therapy is debatable.
When fever is present, antibiotic therapy should be started (quinolones, or cephalosporines are indicated).
According to the site and size of the stone, often the stone can be expelled spontaneously, with expectant approach, with increased fluid intake and analgesic therapy when required (tramadol drops can be a good option). The administration of alpha-blockers can increase the chance of spontaneous passage of the stone.
Frequently the colic is due to the passage of a stone along the ureter, the thin tube connecting the kidney and the bladder. Due to small calibre of the ureter, even a minute stone can be obstructing. 
The chance of spontaneous obstruction is highly depending on the size of the stone.
< 4 mm                        93%
4-6 mm                       50%
   7  mm                       35%
>8 mm                         0-5%
If a stone doesn´t pass within 2-3 weeks, the chance of spontaneous expulsion drops considerably. 
A ureter stone must be treated when:

1. There is a severe hydronephrosis
2. Doesn´t pass spontaneously within 2-3 weeks
3. There is fever not responding to antibiotic therapy
4. There is strong pain not responding to analgesics
5. The size is such that spontaneous passing is very unlikely to happen
6. In patients with single kidney or with bilateral ureteral stones

In case of hydronephrosis with fever and urinary infection, urine should be drained from the kidney before stone treatment. Urine can be drained through the excretory ways, with a thin ureteral catheter, or with a tube through the flank (percutaneous nephrostomy).
The ureteral catheter is introduced with a cystoscopy, with a fiber optic, through the urethra. The catheter is pushed upward until it reaches the kidney. Usually a double J stent is used: it is called like this, because at both ends of the catheter there are two pig-tails, to avoid displacement. The ureteral catheter stays completely inside the body, between the kidney and the bladder, thus by-passing the obstructing stone.
Another option is the emergency drainage of urine through a small tube placed inside the flank, directly into the kidney. The tube (nephrostomy) is fixed to the skin by a stitch, and the urine is collected in a bag. This is a temporary and fast way to obtain drainage of infected urine.
Urinary stone treatment can be performed with several techniques.
The least invasive approach to a stone is Extracorporeal Shock Wave Lithotripsy (ESWL)

A special device produces intermittent shock waves, that are transmitted to the body through a fluid medium (water, or a gel patch). The waves are focused on the stone by ultrasound and/or x-rays. According to size, site, and composition of the stone, multiple procedures may be needed to obtain a good fragmentation. The stone is not dissolved, but fragmented in smaller stones, that can be expelled through the ureter for their reduced size.

The limits of the procedure are related to the stone structure (very hard stone can´t be fragmented), size (stones larger than 20-25 mm are considered too large), or site (stones near the iliac bone may not be treated properly)
For stones of the lower calyx of the kidney, success rate is around 50-60%. For other kidney locations, the success is higher, about 80-90%.
Though the risk of renal haematoma is low, it is higher for patients with hypertension. Patients with severely impaired coagulation shouldn´t undergo ESWL.
Some Authors have reported an increased risk of new hypertension after ESWL, but the data are contradicting. Recently it has been suggested that ESWL might facilitate the onset of diabetes.
When kidney stones are too large for ESWL treatment, the technique of choice is percutaneous lithotripsy. With the patient in prone position, the excretory ways of the kidney are accessed with a needle through the flank. A fiber optic instrument is introduced and the stone is reached.

The stone is fragmented under vision, with ultrasound, laser, or mechanic energy. Major fragments are removed through the instrument. The operation requires general anaesthesia. Success rate is above 90%. Complications are rare, but they may involve renal bleeding.
Stones of the ureter can be treated with ESWL or with ureteroscopy (endoscopy). A thin fiberoptic instrument, about 3 mm in diameter, is introduced through the urethra, the bladder, and up into the ureter, until the stone is met. With the same forms of energy available for percutaneous lithotripsy, the stone is fragmented. The patient can be dismissed in the next 24 hours. The procedure is successful in 85-95% of cases.Open surgery is today very rare, and it is reserved to 2-3% of urinary stones. Usually patients with staghorn stones, filling all the kidney excretory ways, are candidates. In patients with large ureter stones, not responding to ESWL , after failure of ureteroscopy, a laparoscopic approach can be used.

Bladder stones are rarer, and usually they are related to chronic urinary retention, due to voiding obstruction, like in benign prostatic hyperplasia or in urethral strictures. Urinary infection and indwelling catheters are risk factors for bladder stones. Bladder stones can be treated with endoscopic approach, with a fiberoptic instrument through the urethra. Mechanical fragmentation is performed. Very large stones may require surgical approach for removal.