Stones

Stone formation occurs as a result of an imbalance between the solubility of salts and their crystallization. In the Western world, 70-80% of stones are composed of calcium oxalate. Ureteric stones form initially in a renal papilla from a small submucosal concretion. As the crystallization increases, it separates from the papilla and passes into the collecting system with the urine. Before they pass into the calyces, such stones are seldom symptomatic although they can be associated with recurrent urinary infections. Conversely, a staghorn renal calculus that fills the renal pelvis and calyces is formed within the collecting system. Such stones are often seen with urine chronically infected with Proteus mirabilis. This bacterium splits urea to ammonia, alkalinizes the urine and precipitates magnesium ammonia phosphate. This becomes calcified and the stone may form a complete cast of the collecting system.

Treatment

• Small kidney stones can be fragmented by extracorporeal shock wave lithotripsy (ESWL). The technique uses a machine to generate shock waves, which are focussed through the skin and body tissues onto the dense stones, leading to fragmentation. It requires analgesia and careful monitoring afterwards to ensure the stone fragments pass down the ureter satisfactorily.

• Direct access to the renal collecting system via a percutaneous tract can allow larger stones to be removed endoscopically - known as percutaneous nephrolitho-tomy (PCNL).

• Staghorn stones represent a surgical challenge. If there is minimal renal function, then a nephrectomy may be the best way of eradicating the stone and the recurring urine infections. If renal function is good, percutaneous removal of the stone (PCNL) can be attempted. Sometimes fragments remain and these can be removed using ureteroscopy and appropriate fragmentation techniques, such as the laser (see above), or ESWL. Any remaining fragments may act as a nucleus for new stone formation and will act as a reservoir for continuing infection.

• Patients with stones in the ureter usually present acutely, with severe loin pain ('renal colic'). The majority of these stones are <5 mm in diameter and will pass spontaneously. However, larger ureteric stones often require surgical intervention. Various techniques can be utilized, but ureteroscopy and fragmentation (using a laser) is the most widely used, along with ESWL in certain situations.

Figure 19.6. CT: renal cell carcinoma of the left kidney showing (a) pre- and (b) post-contrast images.

• The management of patients with a ureteric stone causing obstruction and in whom the urine becomes infected, represents a urological emergency. Urgent decompression of the infected and obstructed kidney is required by insertion of a percutaneous nephrostomy, or placement of a ureteric stent to 'bypass' the obstruction and allow drainage of the infected urine.

51 Tips for Dealing with Kidney Stones

51 Tips for Dealing with Kidney Stones

Do you have kidney stones? Do you think you do, but aren’t sure? Do you get them often, and need some preventative advice? 51 Tips for Dealing with Kidney Stones can help.

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