**Core Concept:** Jejunal diverticulum is a small pouch-like outpouching of the jejunal wall, usually found in the ileocaecal region. It is a congenital anomaly and is associated with the Meckel's diverticulum.

**Why the Correct Answer is Right:** Jejunal diverticulum is usually a small outpouching of the jejunal wall, which is a rare congenital anomaly. It is often considered a developmental remnant of Meckel's diverticulum, a more common entity that arises from the embryonic yolk sac and is lined by both small and large intestinal mucosa. The correct answer (D) refers to the fact that jejunal diverticulum is a small pouch-like structure within the jejunal wall, which is a characteristic feature of the condition.

**Why Each Wrong Option is Incorrect:**

A. This option incorrectly states that jejunal diverticulum is a type of Meckel's diverticulum. While they share a similar embryological origin, jejunal diverticulum is a distinct entity with its own characteristics.

B. This answer incorrectly suggests that jejunal diverticulum is a type of Meckel's diverticulum. As mentioned above, they are distinct entities with different embryological origins and clinical presentations.

C. This answer incorrectly associates jejunal diverticulum with the caecum or colon. Jejunal diverticulum is a pouch within the jejunal wall, thus it is unrelated to the caecum or colon.

**Clinical Pearl:** In clinical practice, jejunal diverticulum should be differentiated from Meckel's diverticulum, which can lead to complications like bleeding, obstruction, and perforation. Understanding the unique features of jejunal diverticulum helps in appropriate diagnosis and management of the condition.