Hydatid cyst is commonly found in: September 2005
**Core Concept**
Hydatid cyst, also known as echinococcosis, is a parasitic infection caused by the Echinococcus tapeworm. This parasitic disease is characterized by the formation of fluid-filled cysts in various organs, most commonly the liver and lungs.
**Why the Correct Answer is Right**
The correct answer is liver because the Echinococcus tapeworm is primarily ingested by dogs and other canines, which then excrete the eggs in their feces. Humans become infected by ingesting contaminated water, food, or soil containing the eggs. Upon ingestion, the eggs hatch into larvae that penetrate the intestinal wall and migrate to the liver via the bloodstream, where they form cysts. The liver is the most common site for hydatid cyst formation due to its rich blood supply and the fact that it is the first organ encountered by the migrating larvae.
**Why Each Wrong Option is Incorrect**
* **Option A:** The lungs are a secondary site for hydatid cyst formation, but they are not the most common location. This option is incorrect because it underestimates the prevalence of liver involvement.
* **Option B:** The spleen is an uncommon site for hydatid cyst formation, and it is not typically associated with this parasitic infection. This option is incorrect because it is not a recognized site for hydatid cyst formation.
* **Option C:** The kidneys are not typically involved in hydatid disease, and this option is incorrect because it is not a recognized site for hydatid cyst formation.
**Clinical Pearl / High-Yield Fact**
The liver is the most common site for hydatid cyst formation due to its rich blood supply and the migratory pattern of the Echinococcus tapeworm larvae.
**Correct Answer: B. Lungs.**