**Question:** Gangrene of intestine is seen in all the following conditions, except

A. Ischaemic necrosis due to arterial occlusion
B. Gangrene due to venous insufficiency
C. Gangrene due to perforation of intestine
D. Gangrene due to chemical or thermal injury

**Core Concept:**
Gangrene is a condition where tissues die due to lack of oxygen and nutrients, most commonly caused by arterial occlusion, venous insufficiency, or perforation. There are two types of gangrene: ischaemic (arterial) and pyogenic (bacterial). The latter is typically seen in cases of perforation, chemical or thermal injury, or septic embolism.

**Why the Correct Answer is Right:**
Gangrene due to perforation of intestine (option C) is an example of pyogenic gangrene, as it arises from a breach in the intestinal wall allowing bacteria to enter the peritoneal cavity and cause systemic infection. This type of gangrene is not typically caused by arterial or venous insufficiency, making it the correct answer to exclude.

**Why Each Wrong Option is Incorrect:**

A. Ischaemic necrosis due to arterial occlusion (option A) is a common cause of gangrene, particularly in elderly patients with atherosclerosis. This is not the correct answer to exclude.

B. Gangrene due to venous insufficiency (option B) is a rare cause of gangrene due to inadequate blood flow in the affected area, resulting in hypoxia and cellular death. This is not the correct answer to exclude.

C. Gangrene due to chemical or thermal injury (option D) is a type of pyogenic gangrene caused by direct damage to the tissues, often resulting from chemical or thermal agents. This is not the correct answer to exclude.

**Clinical Pearl:**
In cases of suspected gangrene, it is essential to evaluate for the underlying cause, as different treatments are required for ischaemic (arterial) and pyogenic (bacterial) gangrene. For example, ischaemic gangrene may require revascularization, while pyogenic gangrene requires antibiotic therapy and debridement of necrotic tissue. A thorough clinical examination and appropriate investigations are crucial in determining the type of gangrene and guiding appropriate management.