Renal calculi

Aetiology

The subject is complex and the following represents a brief summary of current opinion.

Dietetic. Deficiency of vitamin A causes desquamation of epithelium. The cells form a nidus around which stone is deposited. From a study of economic conditions in places where stones are common, it is evident that the inhabitants do suffer dietary imbalance. It is uncertain whether this mechanism is of importance other than in the formation of bladder calculi.

Altered urinary solutes and colloids. Dehydration leads to an increased concentration of urinary solutes and tends to cause them to precipitate. It has been postulated that reduction of urinary colloids which adsorb solutes or mucoproteins which chelate calcium will also result in a tendency for stone components to come out of solution.

Decreased urinary citrate. The presence of citrate in urine, 300—900 mg/24 hours (1.6—4.7 mmol/24 hours) as citric acid, tends to keep otherwise relatively insoluble calcium phosphate and citrate in solution. The urinary excretion of citrate is under hormonal control and decreases during menstruation.

Renal infection. Infection favours the formation of urinary calculi. Both clinical and experimental stone formation are common when urine is infected with urea splitting streptococci, staphylococci and especially Proteus sp. The predominant bacteria found in the nuclei of urinary stones are staphylococci and Escherichia coli.

Inadequate urinary drainage and urinary stasis. Stones are liable when urine does not pass freely.

Prolonged immobilisation from any cause, e.g. paraplegia, is liable to result in skeletal decalcification and an increase in urinary calcium favouring the formation of calcium phosphate calculi.

Hyperparathyroidism leading to hypercalcaemia and hypercalciuria is found in 5 per cent or less of those who present with radio-opaque calculi. In cases of recurrent or multiple stones this cause should be eliminated by appropriate investigations (see Chapter 45). Hyperparathyroidism results in a great increase in the elimination of calcium in the urine. These patients ‘pass their skeletons in their urine’. A parathyroid adenoma should be removed before definitive treatment for the urinary calculi.

Randall’s plaque and microliths. Randall suggested that the initial lesion in some cases of kidney stone was an erosion at the tip of a renal papilla. Deposition of calcium on this erosion produced a lesion which has been called Randall’s plaque. It has further been shown that minute concretions (microliths) regularly occur in the renal parenchyma and Carr postulated that these particles are carried by lymphatics to the sub endothelial region where they may accumulate. Ulceration of the epithelium exposes the potential calculus to the urine with the result that a stone forms. The importance of Randall’s plaques and Carr’s microliths in most patients with stones is a matter for debate.

Types of renal calculus

Oxalate calculus (calcium oxalate) (Fig. 64.21). Oxalate stones are irregular in shape and covered with sharp projections which tend to cause bleeding. The surface of the calculus is discoloured by the pigments of altered blood. A calcium oxalate monohydrate stone is very hard and absorbs X-rays well; it is easy to see radiologically.

Phosphate calculus [usually calcium phosphate, although sometimes combined with ammonium magnesium phosphate (struvite)] is smooth and dirty white (Fig. 64.22). The stone tends to grow in alkaline urine especially when proteus organisms are present which split urea to ammonium. As a result, the calculus may enlarge to fill all or most of the renal collecting system forming a stag horn calculus (Fig. 64.22). Even a very large stag horn may be clinically silent for years until it signals its presence by causing intractable urinary infection or haematuria. Because they are large, phosphate calculi are usually easy to see on X-ray films.

Uric acid and urate calculi are hard, smooth and often multiple. Their colour varies from yellow to reddish brown and they sometimes have an attractive multifaceted appearance. Pure uric acid stones are radio lucent and appear on an excretion urogram as a filling defect, which can be mistaken for a transitional tumour of the upper urinary tract. In practice most uric acid stones contain some calcium so they cast a faint radiological shadow. In children mixed stones of ammonium and sodium urate are sometimes found. They are yellow soft and friable. They are radio lucent unless they are contaminated with calcium salts.

Cystine calculi are uncommon. They appear in the urinary tract of patients with a congenital error of metabolism which leads to cystinuria. Cystine crystals are hexagonal, translucent white and appear only in acid urine. Cystine stones are often multiple and may grow to form a cast of the renal pelvis and calyces. They are pink or yellow when first removed but they change colour to a greenish hue when exposed to air. Cystine stones are radio-opaque because of the sulphur that they contain, and they are very hard.

Xanthine calculi are extremely rare. They are smooth and round, brick red in colour and show lamellation on cross section.

Clinical features

Renal calculi are very common. Fifty per cent of patients present between the ages of 30 and 50 years. The male:female ratio is 4:3.

The symptoms are variable and the diagnosis sometimes remains obscure until the stone is discovered on a radiograph.

Silent calculus

Some stones, even large stag-horn calculi, cause no symptoms for long periods during which there is progressive destruction of the renal parenchyma. If the calculi are bilateral, uraemia may be the first indication of their presence; although secondary infection usually gives symptoms first.

Pain

Pain is the leading symptom in 75 per cent of people with urinary stone disease.

Fixed renal pain is located posteriorly in the renal angle (Fig. 64.23), anteriorly in the hypochondrium, or in both. It may be worse on movement, particularly on climbing stairs.

Ureteric colic is an agonising pain passing from the loin to the groin. Typically it starts suddenly causing the patient to move around trying in vain to find comfort. Strangury, the painful passage of a few drops of urine, may occur if the stone is in the intramural ureter. An attack of colic rarely lasts more than 8 hours. It is not associated with pyrexia, although the pulse rate usually rises as a reflex response to the severe pain.

Ureteric colic is often caused by a stone entering the ureter but it may also occur when a stone becomes lodged in the pelviureteric junction. The severity of the colic is not related to the size of the stone.

Abdominal examination. During an attack of ureteric colic there is rigidity of the lateral abdominal muscles but not, as a rule, of the rectus abdominis. Percussion over the kidney produces a stab of pain and there may be tenderness on gentle deep palpation. Hydronephrosis or pyonephrosis leading to a palpable swelling in the loin is rare.

Haematuria

  Haematuria is sometimes a leading symptom of stone disease and occasionally the only one. As a rule the amount of bleeding is small.

Pyuria

Infection is likely in the presence of stones and is particularly dangerous when the kidney is obstructed. As pressure builds in the dilated collecting system, organisms are injected into the circulation and a life-threatening septicaemia can quickly develop.

The mechanical effect of stones irritating the urothelium may cause pyuria even in the absence of infection.

Investigation of suspected urinary stone disease

Radiography

Calculi are easier to see if the bowel is empty and it is helpful to administer a vegetable laxative. The ‘scout’ film must show the kidney, ureters and bladder (a ‘KUB’ film). When a renal calculus is branched, there is no doubt about the diagnosis (Fig. 64.24). An opacity that keeps a constant position relative to the urinary tract during respiration is likely to be a calculus within it.

A doubtful opacity can sometimes be shown to be anterior to the vertebral bodies on a lateral radiograph and hence out side the urinary tract (Table 64.4); such is the finding with calcified mesenteric nodes and opacities within the alimentary tract.

Excretion urography

Excretion urography is the most useful investigation to establish the presence of a calculus. It also shows where the stone is and gives important information about the function of the other kidney.

Ultrasound scanning

Ultrasound scanning is of most value in locating stones for treatment by extracotporeal shock wave treatment (see below).