Hydatid Disease and Cyst Management Quiz

Hydatid Diseases

• Hydatid diseases, also known as echinococcosis, are zoonotic diseases.
• Humans contract the disease from dogs.
• The disease is common in sheep-grazing areas globally.
• The causative agents are Echinococcus granulosus, Echinococcus multilocularis, and Echinococcus oligarthrus.

Echinococcus Granulosus

• This is a tapeworm, and a hermaphrodite.
• It resides in the canine's ileum.
• It has a head and three segments.
• The terminal segment contains eggs.
• The head has hooks/suckers.
• It is one of the smallest tapeworms (3-6 mm in length).
• The three proglottids (sections) include an immature first section, a mature second section, and a gravid third section containing eggs.

Hydatid Disease Life Cycle

• The definitive host is usually a dog that consumes organs containing hydatid cysts (e.g., sheep liver).
• The intermediate host (sheep or human) ingests vegetables contaminated with dog feces containing eggs.
• Larvae exit the eggs in the duodenum, and then travel to the liver, lungs, brain, or other organs via the bloodstream, where they develop into cysts.
• The cysts have three layers: outer fibrous layer (host origin), laminated layer (parasite origin), and inner nucleated germinal layer (for generating protoscoleces).
• Protoscoleces (baby tapeworms) bud from the germinal layer, filling the hydatid cyst.
• Cysts can rupture into adjacent organs/the peritoneal cavity.
• Older cysts have a higher risk of daughter cyst formation, which is a complication factor for recurrence.
• The life cycle is completed when dogs consume the entrails of slaughtered sheep.

Hydatid Disease Pathogenesis

• Hydatid cysts act as space-occupying lesions, putting pressure on adjacent tissue.
• Cyst fluid contains parasite antigens that sensitize the host.
• Cyst rupture can lead to anaphylaxis.
• Cyst rupture can also spread protoscoleces widely.
• Cysts can form fistulas (tunnels) into adjacent organs.
• Large fluid-filled (unilocular) cysts contain free scoleces and numerous daughter cysts (called "hydatid sand" which is diagnostically important).

Clinical Features

• Hydatid disease can be asymptomatic.
• Symptoms may be due to pressure effects causing swelling, including abdominal pain, dyspepsia (indigestion), and vomiting.
• Mechanical effects can occur in adjacent organs, such as liver enlargement, and lung cysts eroding into bronchi.
• Lung collapse and cerebral cysts causing headaches/neurological signs are also possible.
• Allergic reactions (causing urticaria or anaphylaxis) can occur due to cyst fluid antigens entering the bloodstream.
• Complications include anaphylaxis/dissemination (rupturing into peritoneum, pleura, pericardium, bronchioles), obstructive jaundice, and bacterial infection leading to abscesses.

Hydatid Diagnosis

• Diagnosis is based on microscopic examination (brood capsules with multiple protoscoleces) or histopathology (detection of cyst layers).
• Aspiration of the cyst fluid is not done when the cyst is inside the body to prevent spillage.
• The Casoni/Asten skin test uses injecting sterile hydatid fluid intradermally, and an immediate reaction within 20 minutes indicates a positive result. However, the test is unreliable because it can remain positive after the cyst has been removed.

Hydatid Investigations

• Imaging plays a key role for detection (X-rays, ultrasonography, CT scan/MRI).
• Ultrasounds can help distinguish cysts (well-circumscribed) from simple cysts, identify multivesicular cysts ("cartwheel sign"), or detect "split-wall sign" due to endo- and ectocyst separation.
• Serology (detection of antibodies to germinal membrane) includes the following:
• Immunoelectrophoresis (IE)
• Complement fixation test (CFT)
• Indirect hemagglutination test (IHT)
• ELISA

Treatment

• Surgical approaches vary, from total resection (e.g., pericystectomy or hepatectomy) to minimal invasive approaches (e.g., percutaneous cyst aspiration) or laparoscopic procedures for hepatic hydatid cysts.
• The choice depends on the patient's condition, number/location of cysts, surgeon's experience, and intensive-care unit availability.
• Conservative management is sometimes used for unfit elderly patients with small, asymptomatic, calcified cysts.
• Surgery is the primary treatment.
• Medical treatment includes preoperative albendazole/mebendazole to reduce spillage complications or for poor surgical candidates/widely disseminated disease.
• Protoscolicidal agents (e.g., hypertonic saline, cetrimide, H2O2, ethanol, silver nitrate) are sometimes injected into the cyst. Formalin can cause biliary damage and isn't typically recommended.