Which of the following is a classic hallmark sign associated with intussusception in infants?

Intussusception involves the telescoping of one intestinal segment into another, causing lymphatic and venous obstruction. Knowledge of gastrointestinal manifestations is critical to identify life-threatening ischemia and bowel necrosis in infants presenting with sudden abdominal pain and stool changes. Choice A rationale Projectile vomiting is a characteristic clinical finding of hypertrophic pyloric stenosis, not intussusception. It results from gastric outlet obstruction due to muscular thickening, occurring without the presence of bile, typically seen in infants aged three to six weeks. Choice B rationale Severe diarrhea typically indicates infectious gastroenteritis or malabsorption syndromes. In intussusception, the bowel is obstructed by the invagination process, which usually prevents the passage of normal diarrheal stools as the intestinal lumen becomes physically blocked and compressed. Choice C rationale Currant-jelly stools contain a mixture of blood and mucus, occurring as the compressed intestinal mucosa sheds. This classic hallmark reflects venous congestion and ischemia within the intussusceptum, indicating a high risk for impending bowel perforation and necrosis. Choice D rationale Bilious vomiting suggests a distal intestinal obstruction but is not specific to intussusception. While it can occur as the condition progresses, it lacks the diagnostic specificity of the vascular-related stool changes that define the classic clinical presentation.