A plain X ray abdomen is performed in case of small bowel obstruction. Small bowel would be called dilated if its diameter is more than:
**Core Concept**
The normal diameter of the small bowel is typically less than 2.5 cm. Dilatation is observed when the diameter exceeds this value due to obstruction. This dilatation can be visualized on an X-ray, indicating the presence of a small bowel obstruction.
**Why the Correct Answer is Right**
The correct answer is based on the radiological criteria for small bowel dilatation. A diameter of more than 2.5 cm is considered dilated, indicating that the bowel is obstructed. This is because the normal peristalsis is disrupted, leading to accumulation of gas and fluid, causing the bowel to dilate. The dilated bowel loops can be visualized on an X-ray, which is a crucial diagnostic tool in cases of suspected small bowel obstruction.
**Why Each Wrong Option is Incorrect**
* **Option A:** A diameter of 1.5 cm is considered normal, not dilated. Therefore, this option is incorrect.
* **Option B:** A diameter of 3.5 cm is indeed dilated, but the question asks for the threshold value, not the range. Therefore, this option is incorrect.
* **Option C:** A diameter of 2 cm is not dilated, as it is less than the threshold value of 2.5 cm. Therefore, this option is incorrect.
**Clinical Pearl / High-Yield Fact**
In cases of small bowel obstruction, the small bowel dilatation is usually preceded by a transition zone, where the dilated bowel meets the normal bowel. This transition zone is a crucial radiological finding that helps in diagnosing small bowel obstruction.
**Correct Answer: C. 2.5 cm**