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
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).