Hydatid cysts are most commonly found in which organ?

• A. Liver
• B. Brain
• C. Spleen
• D. Heart

Answer: (A)

The main idea is that hydatid cysts from Echinococcus infections favor the liver because the parasite’s oncosomes reach the liver first via the portal circulation and the liver acts as the primary filter. After ingestion, the oncospheres cross the intestinal wall and enter the portal vein, so they lodge in hepatic tissue and form cysts there in the majority of cases. If some oncospheres escape this first-pass filter, they can travel to the lungs and form cysts there, which is why the lungs are the next most common site. Involvement of the brain, heart, or spleen is much less frequent because fewer organisms reach those tissues and the conditions there are less favorable for cyst development. This distribution—liver as the most common site, followed by the lungs, with other organs rarely affected—reflects the path the parasite takes through the body.