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Hydatid disease

Etiology:
Hydrated disease in man is caused by the larval stage of Taeniae Echinococcus (T Granulosa). This cystode completes its life cycle in two hosts. The definitive host is dog in whose intestine, large or adult worm is found. The intermediate host is sheep, occasionally man, in whom the egg enters the intestine either by contact with infested dog or from the contaminated food. Parts of Africa, Australia and Mediterranean come under region of high incidence.

Pathology:
Structure of cyst:
  • Wall of cyst:
    Usually wall of the cyst contains germinal epithelium, which secretes externally a fluid that is covered into the laminated membrane and internally the hydatid fluid. Starting from outside to inside the layers are:
    • Adventitia: (Pseudocyst) formed by the reactive fibroses in the surrounding tissues
    • Laminated membrane: (Ectocyst) is multilayered and impervious to noxious agents
    • Germinal Epithelium: is a single layer of cells. Proliferation of these cells produces brood capsules which, keep attached to the germinal layer by pedicles. Within the wall of brood capsule develop 5 to 20 scolices (head of future worms)
  • Content of cysts:
    • Hydatid fluid: is secreted by the germinal cells. It is watery and slightly alkaline. It produces anaphylactic reaction if it escapes into the tissues (by spontaneous rupture of cells or by operation)
    • Hydatid sand: is formed by the disintegrated brood capsules which get detached and fall into the cavity of cyst
    • Daughter cysts: it is the replica of the mother cysts with all layers. It develops from the brood capsule that gets detached and fall in the cavity of mother cyst. This undergoes degeneration following the damage of laminated membrane
  • Development of Hydatid Cyst:
    In duodenum the egg ruptures and liberates the hexacanth embryo. The embryo penetrates intestinal wall and then reaches to the liver via the portal vein. Embryo is caught in the liver filter and hence changes to a larva. This cystic larva is called hydatid cyst. If the embryo escapes the liver filter then it is arrested in lung capillaries where it forms the cyst. If by chance the embryo escapes now also from the lungs, then it enters the systemic circulation to any organ (brain, kidney, muscles, bones etc.) and forms the cyst. The ratio of the presence of hydatid cyst is as follows:
    Liver: 80%
    Lungs: 15%
    Other foci: 5%


Complications:
Rupture:
  • Liver cyst: may rupture into biliary duct, peritoneal cavity, GIT, Pleural cavity etc
  • Lung cyst: it may burst into pleural cavity or bronchus
Infection and suppuration: Repeated infections cause adhesions between adventitia and cystic wall, making enucleation difficult. An infected hepatic cyst may rupture directly into lung tissue through adhered subphrenic and pleural space causing hepatobronchial fistula
Calcification: following death of parasites, calcification may occur
Anaphylactic reactions: may result in urticaria, fever etc.
Investigations:
X-rays: (straight) for calcification
Ultrasonography
CT scans
Allergic tests (Casoni’s Intradermal Test): A wheal formation on skin following intradermal injection of small amount of hydatid fluid
Serological test: include Indirect Agglutination Test and Complement Test
Blood count: shows Eosinophilia

Clinical signs:
  • Pain in the upper right quadrant
  • Palpable mass with secondary infection
  • Tenderness of liver and hepatomegaly
  • Hydatid thrill
  • Spiking temperature
  • Jaundice (if it ruptures in biliary duct) and biliary colic
  • Urticaria and vomiting
Treatment:
MEBENDAZOLE is the treatment of choice.
Surgical treatment:
Drainage of cyst cavity and then closure of the cavity on drainage.

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This article has been written by Dr. M. Javed Abbas.
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00:55 06/02/2003