Which is true regarding hydatid cyst of lung –
**Core Concept**
Hydatid cyst of the lung is a parasitic infection caused by Echinococcus granulosus, characterized by the formation of cystic structures within the lung tissue. This condition arises when the parasite's eggs are ingested, leading to the development of larvae that form cysts in the lung.
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of hydatid cyst formation. The Echinococcus granulosus parasite releases oncospheres, which then develop into protoscoleces within the cyst. The cyst wall is composed of a laminated layer, a nucleated layer, and a germinal layer, which contains the brood capsules and the oncospheres. The cysts can grow and rupture, leading to anaphylactic reactions and potentially life-threatening complications.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the pathophysiology of hydatid cyst formation.
**Option B:** This option is incorrect because the cyst wall is not primarily composed of fibrotic tissue; rather, it has distinct layers of laminated, nucleated, and germinal tissue.
**Option C:** This option is incorrect because the cysts do not typically cause bronchiectasis, although they can cause obstructive symptoms if they grow large enough to compress bronchi.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of hydatid cyst of the lung is the presence of a "hydatid ring" or "hydatid wheel" sign on chest radiographs, which is caused by the calcification of the cyst wall.
**Correct Answer: D.**