## Why "Intussusception with ileocolic telescoping" is right The concentric ring or "target" sign (marked **A**) on transverse ultrasound is the hallmark diagnostic finding of intussusception. This appearance results from telescoping of the proximal bowel segment (usually ileum) into the distal segment (colon), creating concentric layers of mucosa, submucosa, and muscle. The clinical presentation—a 14-month-old (peak age 6 months–2 years) with intermittent colicky pain, vomiting, lethargy, and a RUQ mass—combined with the target sign on USG is pathognomonic for intussusception. Ileocolic intussusception accounts for ~90% of cases and is the most common cause of intestinal obstruction in infants. (Nelson 21e Ch 358; Bailey & Love 28e) ## Why each distractor is wrong - **Acute appendicitis with perforation**: Does not produce a concentric ring sign on USG. Appendicitis presents with focal RLQ tenderness and a dilated, non-compressible appendix; the target sign is specific to intussusception. - **Mesenteric lymphadenitis from viral gastroenteritis**: Causes enlarged mesenteric lymph nodes on USG but does not produce the characteristic target sign. While viral prodrome may precede intussusception, lymphadenitis alone does not cause the telescoping appearance. - **Hirschsprung disease with enterocolitis**: Presents with abdominal distension, explosive diarrhea, and fever in a neonate/young infant; does not produce a target sign. Diagnosis is by contrast enema (transition zone) and rectal biopsy, not by the imaging finding shown. **High-Yield:** The target sign on transverse USG is diagnostic of intussusception; ileocolic type is most common (~90%) in infants 6 months–2 years; lethargy can be the predominant feature and should not delay diagnosis. [cite: Nelson 21e Ch 358; Bailey & Love 28e]
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