Stone disease of the urinary tract

Published on 11/04/2015 by admin

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37

Stone disease of the urinary tract

Introduction

Stone disease is second only to prostatic disease in the overall urological workload. Stones may occur in all parts of the urinary tract, including the pelvicalyceal system of the kidney, the ureter, the bladder and even sometimes the urethra. Stones most commonly provoke symptoms due to obstruction or by predisposing to urinary tract infections.

The pattern of stone disease has changed markedly over the last 150 years. Bladder stones were once common and were one of the few conditions successfully treated by surgery. ‘Cutting for stone’, or lithotomy (lithos = stone), was often performed by itinerant surgeons. They used a perineal approach, placing the patient in the manner still described as the lithotomy position.

Upper tract calculi are much more common than bladder calculi and the incidence is rising. Stones range from the uncommon staghorn calculus which fills the pelvicalyceal system, to small stones developing in the pelvicalyceal system that can migrate and obstruct the ureter. Acute ureteric obstruction causes severe pain and presents as the surgical emergency ureteric colic. Most stone disease is, however, asymptomatic or else presents non-urgently to the outpatient clinic.

In developed countries stone disease in childhood is now rare. It peaks in the 20s and 30s and declines slowly thereafter (Fig. 37.1). Males are affected two and a half times more often than females. There is also a high incidence of recurrent stones.

Pathophysiology of stone disease

Chemical composition

Stones are often formed from a mixture of chemical substances and minerals (e.g. calcium and oxalate) when their concentration exceeds their solubility in urine. Intermittent periods of super-saturation due to dehydration, following meals or medical conditions, can lead to the earliest phase of crystal formation. Lack of crystallisation inhibitors in the urine may also play a role in stone formation. Table 37.1 provides a simple chemical classification showing the relative frequency of stone types and their important clinical characteristics and aetiology. Calcium is present in approximately 80%, as oxalate or phosphate compounds or both. The aetiology of stone disease is multifactorial in most cases.

Mechanisms of stone formation

Other predisposing factors

A specific predisposing factor can be detected in a further minority of cases. These include chronic infection, urinary stasis and foreign bodies, and are summarised in Box 37.1.

Box 37.1   Predisposing factors in stone formation

• Idiopathic (most common)

• Stasis of urine, particularly when associated with infection—e.g. congenital abnormalities, hydronephrosis, chronic obstruction (e.g. benign prostatic hyperplasia, neurogenic bladder)

• Chronic urinary infection (urea-splitting organisms, e.g. Proteus, cause alkaline urine and the development of magnesium–ammonium–phosphate stones, typically the ‘staghorn’ calculi of the renal pelvis—see Fig. 37.2)

• Excess urinary excretion of stone-forming substances—e.g. idiopathic hypercalciuria (calcium stones), hyperparathyroidism (calcium stones), hyperoxaluria (oxalate stones), gout (uric acid stones), cysteinuria (cysteine stones), xanthinuria (xanthine stones)

• Foreign bodies—e.g. fragments of catheter tubing, self-inserted artefacts, parasites (schistosome ova), fragments of diseased tissue (e.g. renal papillary necrosis)

• Dietary—e.g. over-consumption of dairy or high calcium content in water

• Multifactorial—e.g. prolonged immobility, children in the developing world, multiple fractures and paralysis (skeletal decalcification)

Clinical features of stone disease

The clinical problem of discrete urinary stones should not be confused with calcification of the renal parenchyma, which can be a feature of tuberculosis and medullary sponge kidney. These and similar diseases can usually be diagnosed by their characteristic X-ray appearance.

The clinical presentation of stones depends on the size, morphology and site of the stone(s). Many cause no symptoms but represent a potentially serious problem. Other stones produce marked pathological effects which present with acute or chronic symptoms or are discovered incidentally on investigation of unrelated symptoms. The presentation of urinary tract stones is summarised in Box 37.2.

Box 37.2   Presentation of stones in the urinary tract

Urinary tract stones produce their injurious effects in three main ways:

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