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 causitive agent of hydatid cyst is Echinococcus Granulosus ( see life cycle of echinococcus granulosus).

Pathogenesis:

Echinococcus granulosus is responsible for formation of unilocular cyst. Cyct 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 contain parasite antigen which may sensitize the host. Dangerous anaphylactic reaction takes place if cyst ruptures spontaneously or during surgical procedures.

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

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

2. Microscopy:
Cyst is observed under 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 eosinophills)

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, sorrounded by a concentric red zone, which later diappears with the wheal.

6. Radiology
Owing to saline contents, cyst is relatively opaque and casts a characteristic circular shadow with 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 release of protosclices 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.