**Core Concept**
The Azzopardi effect is a characteristic histopathological feature observed in small cell carcinoma of the lung, where DNA from necrotic tumor cells is deposited on the walls of blood vessels. This phenomenon is a result of the interaction between the necrotic cells and the vascular endothelium.

**Why the Correct Answer is Right**
The Azzopardi effect is a result of the breakdown of DNA from the necrotic tumor cells, which then interacts with the vascular endothelium, leading to the deposition of DNA on the vessel walls. This is due to the presence of endonucleases that break down the DNA, which is then phagocytosed by the endothelial cells, resulting in the characteristic pattern seen on histopathological examination. The Azzopardi effect is a key diagnostic feature of small cell carcinoma of the lung.

**Why Each Wrong Option is Incorrect**
**Option A:** Psammoma bodies are concentrically laminated calcifications seen in papillary thyroid carcinoma, not small cell carcinoma of the lung.
**Option C:** Button collar lesions are a characteristic feature of basal cell carcinoma of the skin, not small cell carcinoma of the lung.
**Option D:** Necrotic diathesis is a term used to describe the presence of necrosis in tissues, but it is not a specific histopathological feature associated with small cell carcinoma of the lung.

**Clinical Pearl / High-Yield Fact**
The Azzopardi effect is a key diagnostic feature of small cell carcinoma of the lung, and its presence should raise suspicion for this malignancy, particularly in patients with a history of smoking.

✓ Correct Answer: B. Azzopardi effect