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Figure 21.20 Microscopy shows three layers in the wall of hydatid cyst. Inbox in the right photomicrograph shows a scolex with a row of
hooklets.

MORPHOLOGIC FEATURES. Hydatid cyst grows predispose an individual to hepatic drug injury such as pre-
slowly and may eventually attain a size over 10 cm in existing liver disease, aging, female sex and genetic inability
diameter in about 5 years. E. granulosus generally causes to perform a particular biotransformation.
unilocular hydatid cyst while E. multilocularis results in HEPATOTOXICITY. Toxic liver injury produced by drugs
multilocular or alveolar hydatid disease in the liver. and chemicals may virtually mimic any form of naturally-
The cyst wall is composed of 3 distinguishable zones— occurring liver disease. In fact, any patient presenting with CHAPTER 21
outer pericyst, intermediate characteristic ectocyst and inner liver disease or unexplained jaundice is thoroughly
endocyst (Fig. 21.19): questioned about history of drug intake or exposure to
1. Pericyst is the outer host inflammatory reaction chemicals. Hepatotoxicity from drugs and chemicals is the
consisting of fibroblastic proliferation, mononuclear cells, commonest form of iatrogenic disease. Severity of
eosinophils and giant cells, eventually developing into hepatotoxicity is greatly increased if the drug is continued
dense fibrous capsule which may even calcify. after symptoms develop.
2. Ectocyst is the intermediate layer composed of Among the various inorganic compounds producing
characteristic acellular, chitinous, laminated hyaline hepatotoxicity are arsenic, phosphorus, copper and iron.
material (Fig. 21.20). Organic agents include certain naturally-occurring plant
3. Endocyst is the inner germinal layer bearing daughter toxins such as pyrrolizidine alkaloids, mycotoxins and
cysts (brood-capsules) and scolices projecting into the bacterial toxins. The synthetic group of organic compounds
lumen. are a large number of medicinal agents. In addition, exposure
Hydatid sand is the grain-like material composed of to hepatotoxic compounds may be occupational,
numerous scolices present in the hydatid fluid. Hydatid environmental or domestic that could be accidental,
fluid, in addition, contains antigenic proteins so that its homicidal or suicidal ingestion. The Liver, Biliary Tract and Exocrine Pancreas
liberation into circulation gives rise to pronounced In general, drug reactions affecting the liver are divided
eosinophilia or may cause anaphylaxis. into two main classes:
1. Direct or predictable, when the drug or one of its
CHEMICAL AND DRUG INJURY metabolites is either directly toxic to the liver or it lowers
the host immune defense mechanism. The adverse effects
HEPATIC DRUG METABOLISM. The liver plays a central occur in most individuals who consume them and their
role in the metabolism of a large number of organic and hepatotoxicity is dose-dependent e.g. carbon tetrachloride.
inorganic chemicals and drugs which gain access to the body
by inhalation, injection, or most commonly, via the intestinal 2. Indirect or unpredictable or idiosyncratic, when the
tract. The main drug metabolising system resides in the drug or one of its metabolites acts as a hapten and induces
microsomal fraction of the smooth endoplasmic reticulum hypersensitivity in the host. In many instances, drug
of the liver cells via P-450 cytochrome and cytochrome hepatotoxicity is associated with appearance of
reductase enzyme systems. Other steps involved in the drug autoantibodies to liver-kidney microsomes (i.e. anti-LKM2)
metabolism are its conjugation with an endogenous mole- directed against cytochrome P450 enzyme. The hepato-
cule, its active transport from the hepatocytes and ultimately toxicity by this group does not occur regularly in all
its excretion in the bile or in urine depending upon the individuals and the effects are usually not dose-related e.g.
molecular weight of the substance. A number of risk factors acetaminophen.