**Core Concept**
Hydatid cysts, caused by the parasite *Echinococcus granulosus*, require a treatment approach that balances the risk of rupture and anaphylaxis with the need to remove the cyst. The treatment of choice depends on the size, location, and number of cysts, as well as the patient's overall health.

**Why the Correct Answer is Right**
Percutaneous drainage, also known as PAIR (puncture, aspiration, injection, and re-aspiration), is a minimally invasive procedure that involves puncturing the cyst with a needle, aspirating its contents, and then injecting a scolicidal agent to kill any remaining parasites. This approach is preferred for uncomplicated cases, as it reduces the risk of complications associated with surgical excision. The scolicidal agent used is usually a hypertonic saline solution or a formaldehyde-based solution. The procedure is often performed under ultrasound guidance to ensure accurate placement of the needle and to monitor the aspiration process.

**Why Each Wrong Option is Incorrect**
**Option A:** Excision of cyst is a more invasive procedure that is typically reserved for cases where percutaneous drainage is not feasible or has failed. It carries a higher risk of complications, such as anaphylaxis and recurrence.
**Option C:** Conservative management is not a recommended approach for hydatid cysts, as it may lead to cyst growth and rupture, resulting in severe complications.
**Option D:** None is incorrect, as percutaneous drainage is a recognized and effective treatment option for hydatid cysts.

**Clinical Pearl / High-Yield Fact**
The PAIR procedure is most effective when performed in the early stages of the disease, before the cyst has undergone significant calcification or has ruptured. This approach can reduce the risk of complications and improve outcomes.

**✓ Correct Answer: B. Percutaneous drainage**