Liver micro

• Infection with hydatid cyst usually occurs in childhood but manifests in adult life.
• The clinical manifestations of hydatid cyst infection are related to the deposition of the hydatid cysts in various organs, with the most common site being the liver (60-70%, right lobe) or lung (20%).
• Other organs affected by hydatid cyst infection include kidney, muscle, spleen, soft tissue, brain, bone, and others.
• Hydatid cysts can grow up to 5-10 cm in size within the first year and can survive for years or even decades, without any symptoms.
• Few patients with hydatid cyst infection may develop symptoms, which may be attributed to factors such as pressure effect of enlarging cyst, obstruction, secondary bacterial infection, and hypersensitivity due to the release of various allergens from the cyst.
• The outcome of hydatid cyst infection depends on the cyst size and location.
• Younger children are more associated with extrahepatic cysts in the lungs, brain, etc.
• Man acts as an intrasual intermediate host for herbivores, serving as a dead end.
• Bes are the infective form of Echinococcus.
• Cyst wall consists of three layers: Outer pericyst (host derived), middle ectocyst, and inner endocyst.
• Van, a human, acquires the infection by ingestion of food contaminated with dog's feces containing Echinococcus granulous eggs.
• In the duodenum, the embryo or oncosphere of Echinococcus is released, which penetrates the intestinal wall, enters the portal circulation, and is carried to the liver (60-70% of cases) or rarely to other organs.
• Although majority of embryo are destroyed by host immune response, few escape and develop into fluid filled bladder-like cyst called as hydatid cysts.
• The adult worms sexually mature and self-fertilize to produce eggs which are passed in feces and are infective to man.
• Hydatid cyst is a fluid-filled bladder-like cyst, with an average size of 5-8 cm.
• Pathogenicity is related to the deposition of the hydatid cysts (larval form of the parasite) in various organs.
• Man is a dead end, as dogs do not feed on human viscera and therefore the cycle stops there.
• Dogs acquire infection by consuming the contaminated viscera of intermediate hosts such as sheep, which contain hydatid cysts.
• The hydatid cyst (larva) transforms into an adult worm in the dog's intestine.
• This stage is infective to dogs and other definitive hosts.
• Brood capsule: The inner side of the endocyst gives rise to the brood capsule which contains a number of protoscolices (future head)

  • Hydatid fluid: It is a clear, pale yellow-colored fluid, which is antigenic, toxic, and anaphylactic

  • Hydatid sand: Some of the brood capsules and protoscolices break off and get deposited at the bottom as hydatid sand

  • Fate: The hydatid cyst may undergo—(i) spontaneous resolution, or (ii) rupture of the cyst, which may lead to either formation of secondary cysts (carried to other organs) or an anaphylactic reaction to the hydatid fluid antigens.
• Cystic Echinococcosis, also known as Hydatid Disease, is caused by Echinococcus granulosus, also called dog tapeworm.
• Cystic Echinococcosis is a tissue cestode that exists in three morphological forms: adult worm, larva, and egg.
• The adult worm of Cystic Echinococcosis resides in the dog's intestine and measures 3-6 mm long.
• The adult worm of Cystic Echinococcosis has a head, neck, and strobila (body) comprising three proglottids/segments.
• The larva of Cystic Echinococcosis is called hydatid cyst and is the pathogenic form, producing cystic lesions in the liver and other viscera of man and other herbivores.
• The eggs of Cystic Echinococcosis are the infective form, consisting of an embryo with six hooklets surrounded by an embryophore.
• The eggs of Cystic Echinococcosis are morphologically similar to Taenia eggs.
• US is the imaging method of choice for the diagnosis of hydatid disease.
• Hydatid fluid microscopy: Fluid aspirated from a surgically removed hydatid cyst can be subjected to direct mount or staining with acid-fast staining-detects brood capsules and protoscolices.
• Histological examination: Surgically removed cysts can be subjected to histopathological stains like hematoxylin and eosin (H & E) to demonstrate the three layers of the cyst wall and attached brood capsules.
• Antibody detection: A two-step approach-first, a more sensitive screening test such as ELISA (using B2t antigen) or DIGFA (dot immunogold filtration assay) is carried out.
• If found positive, should be confirmed with a more specific test such as a immunoblot (western blot), which is the most specific serological method; detects antibodies to hydatid cyst fluid antigen or antigen B fragment.
• Imaging methods such as X-ray, USG, CT scan, MRI, etc can be performed.
• Ultrasound guided (USG) helps in determining the exact location of cyst, size of cyst, number of cysts, and activity (active or dormant).
• USG is used to monitor the response to treatment.
• The membranes of hydatid cyst may be detached and floating within the cyst cavity, a condition known as the water-lily sign.
• Computed tomography (CT) scan is superior to USG to detect smaller cysts, and extrahepatic cysts, and to differentiate hydatid cyst from other cystic lesions.
• Magnetic resonance imaging (MRI) has a higher contrast resolution, which makes cysts clearer, but poorly detects the calcified cysts.
• Molecular methods, such as polymerase chain reaction (PCR) targeting mitochondrial DNA, have been developed for the diagnosis of hydatid cyst.