Hydatid Cyst - Causes, Pathogenesis, Clinical findings, Laboratory Diagnosis and Treatment.

Hydatid Cyst:

Hydatid cyst is a fluid-filled cyst present most commonly in the liver. other sites where hydatid cyst may develop include lungs, brain and other organs (where oncosphere settles, discussed here in life cycle). It contains fluid and from the inner side of the cyst number of brood-capsules develop. With in each brood capsule, thousands of protoscolices are developed. ( to find out what are
protoscolices and brood capsule click here )

Cause:

The causative agent of hydatid cyst is Echinococcus granulosus ( see the life cycle of Echinococcus granulosus).

Pathogenesis:

Echinococcus granulosus is responsible for the formation of a unilocular cyst. Cyst contains thousands of individual protoscolices as well as many daughter cysts. Cysts act as space-occupying lesion and put pressure on adjacent tissues.
Cyst fluid contains parasite antigen which may sensitize the host. The dangerous anaphylactic reaction takes place if the cyst ruptures spontaneously or during surgical procedures.

Clinical Findings:
1. It may be asymptomatic.
2. If present in the liver, it may induce hepatitis and hepatic dysfunction
3. lung cyst may erode into the bronchus which induces bloody sputum
4. Cerebral cyst induces headache and focal neurologic symptoms
5. Superficial cyst causes visible swelling.
6. Ruptured cyst causes severe anaphylactic shock and localized or generalized secondary echinococcosis.

Laboratory Diagnosis:
1. Specimen:
Blood, serum, cysts enucleated surgically.

2. Microscopy:
A cyst is observed under a microscope for the presence of brood capsules containing multiple protoscolices.
although an accurate diagnosis may be made by withdrawing only a few ml of hydatid fluid by exploratory cyst puncture, it is not advised due to the risk of anaphylactic shock.

3. Blood Examination.
may reveal eosinophilia (increased number of eosinophils)

4. Serology
a. Precipitin reaction
b. complement fixation test
c. flocculation test
d. Hemagglutination test.

5. Casoni's Reaction:
Procedure;
0.2 ml of hydatid fluid is injected intradermally into a suspected patient. In positive reaction A wheal is produced in about 15 minutes, surrounded by a concentric red zone, which later disappears with the wheel.

6. Radiology
Owing to saline contents, the cyst is relatively opaque and casts a characteristic circular shadow with a sharp outline.

hydatid cyst (containing daughter cysts)  in the right lobe of liver

Treatment:
1. surgical removal of cyst:
extreme care must be exercised to prevent the release of protoscolices during surgery. protoscolicidal agent, for example, hypertonic saline should be injected into the cyst to kill the organisms and to prevent accidental dissemination.
In inoperable cases, either mebendazole (drug of choice) or Albendazole is given.