Gallstones (cholelithiasis)
Gallstones are the most common biliary pathology. Indeed,
cholecystectomy is the commonest surgical procedure in the abdomen in the
Western world. Gallstones are classified according to their chemical composition
into cholesterol stones, mixed stones and pigment stones. Cholesterol stones
consist almost entirely of cholesterol and are often solitary (cholesterol
solitaire). Mixed stones account for 90 per cent of gallstones. Cholesterol is
the major component. Other components include calcium bilirubinate, calcium
phosphate, calcium carbonate, calcium palmitate and proteins. Usually they are
multiple, and they are often faceted. Pigment stones are most common in the Far
East and are composed almost entirely of calcium bilirubinate. They are mostly
small and multiple. Some are hard and coral-like, whereas others are soft and
really concretions of sludge rather than stones (Fig.
Gas
in gallstones
Rarely the centre of a stone may contain radiolucent gas in a triradiate
or biradiate fissure and this gives rise to characteristic dark shapes on a
radiograph — the ‘Mercedes Benz’ or ‘seagull’ signs.
Limey
bile
‘Lime-water’ bile is revealed on a plain radiograph (Fig. 54.5)
more clearly than if the gall bladder has been visualised by
cholecystography. The opacity is the result of the gall bladder becoming filled
with a mixture of calcium carbonate and calcium phosphate, usually the
consistency of toothpaste. The condition tends to occur when there is a gradual
obstruction of the cystic or common bile duct, for example due to chronic
pancreatitis or carcinoma of the pancreas. Organisms are rarely grown from the
emulsion.
Incidence
of gallstones
A ‘fat, fertile, flatulent, female of fifty’ is the classical
sufferer from symptomatic gallstones. Useful as this clinical memorandum is,
it should be tempered with the knowledge that cholelithiasis occurs in both
sexes from childhood to the centenarian. In men the disease tends to occur in
the older age groups at which point the incidence is equal to that of women.
Stones are rarer in Africa and in southern India, but not in north India.
Causal
factors in gallstone formation
The aetiology of gallstones is probably multifactorial. Factors
implicated are: (1) metabolic; (2) infective; and (3) bile stasis.
Cholesterol
and mixed stones
Metabolic
Cholesterol, insoluble in water, is held in solution by a detergent
action of bile salts and phospholipids with which it forms micelles (Fig. 54.31).
Bile containing cholesterol stones has an excess of cholesterol relative to
bile salts and phospholipids, thus allowing cholesterol crystals to form. Such
bile is termed ‘supersaturated’ or ‘lithogenic’. Bile cholesterol
increases with age and is raised in women, particularly those taking the
contraceptive pill, in obesity and by clofibrate — a drug used in the
treatment of certain hyperlipoproteinaemias. The concentration of bile salts
in bile is reduced by oestrogens, and also by factors which interrupt the
intrahepatic circulation of bile salts (e.g. ileal disease, resection or bypass
and cholestyramine therapy). These conditions are all associated with an
increased incidence of stones, but there are still some people with cholesterol
supersaturation who remain free of stones, suggesting that there are other
factors of importance.
Infection
The role of infection in causing stones is unclear. Often bile from
patients with gallstones is sterile, but organisms have been cultured from the
centres of gallstones: the radiolucent centre of many gallstones may represent
mucus plugs originally formed around bacteria (Moynihan’s aphorism: ‘A
gallstone is a tombstone erected to the memory of the organism within it’). Helicobacter
pylori antigens have been isolated within gall bladders containing stones.
Bile
stasis
Gall bladder contractility is reduced by oestrogens, in pregnancy and
after truncal vagotomy, situations in which the incidence of gallstones is
increased. Patients on long-term parenteral nutrition have a high incidence of
stones. Lack of good oral intake precludes the release of cholecystokinin, the
hormonal stimulant of gall-bladder contraction released from the duodenal mucosa.
Pigment stones are seen in patients with
haemolysis in which bilirubin production is increased. Examples are hereditary
spherocytosis, sickle cell anaemia, thalassaemia, malaria and mechanical
destruction of red cells by prosthetic heart valves. Pigment stones are found in
the ducts of patients with benign and malignant bile duct strictures. Pigment
stones in Oriental countries are associated with infestations of the biliary
tree by Clonorchis sinensis and Ascaris
lumbricoides. Escherichia coli is often found in the bile of these patients.
This bacterium produces the enzyme t3-glucuronidase which converts the bilirubin
into its unconjugated insoluble form. These stones are often present throughout
the biliary tree including the intrahepatic ducts.
Stones are found throughout the biliary tract and their complications
relate to obstruction of the cystic duct, of the intrahepatic radicals or of
the ampulla of Vater. Obstructive complications may be aggravated by the
presence of infection leading to cholangitis and abscess formation.
Nevertheless, gallstones can be asymptomatic; it is estimated that between 85
and 90 per cent of patients who have gallstones remain asymptomatic. In the UK
the prevalence of gallstones at the time of death is estimated to be 17 per cent
and possibly increasing. Thus, the mere presence of gallstones is not an
indication for a surgical approach. For this reason symptoms must be analysed
with care. A typical patient may fulfil Saint’s triad having gallstones,
diverticulosis of the colon and a hiatus hernia, yet with symptoms that cannot
be directly contributed to any of these. When considering management of a
patient with gastrointestinal symptoms it is important to take a specific
history and consider whether or not the pain from which the patient suffers is
typical or not of biliary tract disease.
Effects and complications of gallstones
• In the gall
bladder:
— Silent stones
— Chronic cholecystitis
— Acute cholecystitis
— Gangrene
— Perforation
— Empyema
— Mucocele
— Carcinoma
• In the bile ducts:
— Obstructive jaundice
— Cholangitis
— Acute pancreatitis
• In the intestine:
— Acute intestinal obstruction (‘gallstone ileus)