A variety of agents have been used as protoscolicides in patients with cystic echinococcosis. No single agent has been proven to be completely safe and effective. Certain factors can increase problems associated with their use.
Problem
Cause
dilution of agent
large cyst incompletely drained
insufficient volume of agent used
small volume in a large cyst
failure to penetrate and reach parasite
presence of honeycombing or daughter cysts
insufficient duration of action
require at least 15 minutes of contact before being drained
drainage into biliary tract, with risk of chemical sclerosing cholangitis
large hepatic cyst in contact with biliary system; formalin should not be used due to high risk of toxicity
where:
• If the cyst is spherical then the volume can be calculated. If the amount of fluid can be estimated on ultrasound, then the amount of dilution of the agent can be calculated.
Choice of protoscolicide - agents effective and relatively safe:
(1) 15-20% hypertonic saline
(2) 70-95% ethanol
(3) 0.5% cetrimide
Choice of protoscolicide - agents not recommended:
(1) formalin (due to toxicity)
(2) hydrogen peroxide (unstable)
The aspirate from a hepatic cyst should be examined for bile, which serves as the marker for contact with the biliary system. These can either be drained surgically or treated with the least toxic protoscolicide.
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