**Question:** While examining radiographs and angiograms of a 52-year-old patient, a physician is trying to distinguish the jejunum from the ileum. He has observed that the jejunum has:

A. Smooth contour and lack of mesenteric fat
B. Thickened wall with increased mesenteric fat
C. Short and wide mesentery
D. Thickened wall with increased mesenteric fat

**Correct Answer:** D. Thickened wall with increased mesenteric fat

**Core Concept:** Distinguishing jejunum from ileum is important in radiography and angiography as it helps in accurate diagnosis of various gastrointestinal conditions. Jejunum and ileum are the two parts of the small intestine, with jejunum being the more proximal and ileum being the more distal segment.

**Why the Correct Answer is Right:** The correct answer, D, is based on the key anatomical differences between the jejunum and ileum. The jejunum has a thicker wall due to its rapid transit time, while the ileum has a thinner wall due to its slower transit time. Additionally, the jejunum has a smooth contour and lacks mesenteric fat, while the ileum has a widened and wavy appearance with a presence of mesenteric fat.

**Why Each Wrong Option is Incorrect:**

A. Jejunum, with its smooth contour and absence of mesenteric fat, does not exhibit these characteristics.
B. Thickening of the ileum wall is not a distinguishing feature between jejunum and ileum, as both segments have a similar wall thickness.
C. Although the jejunum has a short and wide mesentery, this feature is not specific to jejunum and can also be seen in ileum.
E. Thickening of the jejunum wall is incorrect because the jejunum has a thicker wall due to its rapid transit time, not thickening.

**Clinical Pearl:**

Understanding the differences between jejunum and ileum is essential for accurate interpretation of abdominal imaging studies. Jejunum and ileum can both have thickened walls due to inflammation or mass lesions, but the presence of mesenteric fat and the absence of mesenteric fat are significant distinguishing features between the two.