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Hydatid Cyst of the Liver

Epidemiology

  • More common in rural regions
  • Endemic in the Mediterranean, Middle East, South America, China

Etiology

  • Zoonotic infection caused by the tapeworm Echinococcus
    • E. granulosus – causes cystic echinococcosis (most common)
    • E. multilocularis – causes alveolar echinococcosis

Life cycle of E. granulosus

Definitive host – dog

  • Ingests infected sheep offal
  • E. granulosus develops in the dog’s intestine into a parasite – released eggs, which are passed in the dog faeces

Intermediate hosts – humans (and sheep/cattle)

  • Ingest crops contaminated by dog faeces and eggs
  • Egg hatches inside small intestine of human – releases larva that moves through the circulatory system
    • Especially liver (through portal vein) and lungs
  • Once in the organ, larva develops into a cyst

Pathophysiology

3 layers of the cyst 
  • Adventitia (pseudocyst) – an inseparable fibrous tissue due to reaction of the liver to the parasite
  • Laminated membrane (ectocyst) – formed of the parasite itself; contains hydatid fluid
  • Germinal epithelium – only living part lining the cyst (endocyst). This layer secretes hydatid fluid, brood capsules with scolices (heads of future worms)

Disease course

  • Parasite may die and cyst eventually calcifies
  • Commonly cyst enlarges an is palpable per abdomen
  • Rupture into biliary tree – most common
  • May cause complications e.g. jaundice due to pressure over biliary tree
  • Rupture into peritoneal cavity – anaphylactic reaction, life threatening shock
  • Secondary infection – causes suppuration and septicaemia
  • Secondary cysts in lung, spleen, mesentery
  • Hepatic dysfunction
  • Disseminated abdominal hydatidosis after silent rupture

Clinical features

  • Can be asymptomatic
  • Palpable liver with classical thrill (hydatid thrill) – elicited by 3 finger test
  • Jaundice and pain
  • Features of anaphylaxis
  • Discomfort in right upper quadrant, dyspepsia, weight loss, fatigue, vomiting
  • Occasionally – splenomegaly, pleural effusion, cholangitis, fever
  • Water lily sign – following intrabiliary rupture, gas enters into cyst causing partial collapse of cyst wall

Investigations

  • US diagnostic – shows rosettes of daughter cysts, double contoured membranes, calcification of cyst wall
  • XR – calcification
  • CT abdomen
  • Water lily sign   – following intrabiliary rupture, gas enters into cysts causing partial collapse of cyst wall
  • Serologic tests – ELISA, latex agglutination
  • Liver function tests
  • MRI – to visualise biliary tree in case of jaundice
  • ERCP – endoscopic retrograde cholangio-pancreatography

Treatment

Drugs

  • Albendazole – ovicidal/larvicidal. 4 week cycles with 2 week drug free interval
  • Praziquantel – 60mg/kg with albendazole
  • Mebendazole – 600mg daily for 4 weeks

PAIR – Puncture, Aspiration, Injection, Reaspiration

  • Done under US/CT guidance
  • Cyst punctured under local anaesthesia and fluid is aspirated
  • Radiopaque dye is injected to visualise any communication present
  • Scolicidal agent injected into cyst and after 20 minutes reaspiration is done
    • Scolicidal agents – alcohol, hypertonic saline, hydrogen peroxide

Surgery

  • Laparoscopic pericystectomy and liver resection – gold standard therapy
  • Fluid aspirated and scolicidal agent injected
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