**Core Concept**
Intussusception is a medical emergency characterized by the telescoping of a portion of the intestine into another adjacent portion, leading to bowel obstruction and potentially life-threatening complications. This condition is most commonly seen in children, but it can also occur in adults.

**Why the Correct Answer is Right**
Intussusception is frequently associated with a lead point, which is a mass or lesion that initiates the telescoping process. The most common lead points in children are lymphoid hyperplasia and intussusception itself. However, in adults, the lead points are more likely to be neoplastic, such as a gastrointestinal tumor. The mechanism involves the prolapse of the intussusceptum (the portion of the intestine that invaginates) into the intussuscipiens (the surrounding portion of the intestine), leading to bowel obstruction and ischemia.

**Why Each Wrong Option is Incorrect**
**Option A:** Viral gastroenteritis is not a direct cause of intussusception, although it may be a preceding condition that leads to the development of lymphoid hyperplasia.
**Option B:** Meckel's diverticulum is a possible lead point for intussusception, but it is not the most common association.
**Option C:** Gastrointestinal malignancies are a possible cause of intussusception in adults, but they are not the most frequently associated condition.

**Clinical Pearl / High-Yield Fact**
Intussusception is a classic example of a "lead point" causing a mechanical obstruction, and it's essential to identify the underlying cause, whether it's a tumor, a Meckel's diverticulum, or lymphoid hyperplasia.

**Correct Answer:** D.