Hallmark Clinical Sign of Intussusception in Infants
The hallmark clinical sign of intussusception in an infant is sudden, loud crying with drawing up of the knees to the chest (Option C), representing the characteristic intermittent, crampy abdominal pain that occurs with this condition.
Classic Clinical Presentation
The most distinctive feature of intussusception is intermittent, colicky abdominal pain that manifests as sudden episodes of intense crying with the infant drawing their knees up to the chest, followed by periods of relative calm between episodes 1, 2. This intermittent pattern reflects the telescoping bowel causing episodic obstruction and pain 2.
- Most patients present with this intermittent abdominal pain as the primary symptom 2
- The pain episodes are crampy in nature and may progress to bloody stools and lethargy 1
- This presentation is unusual in the first 3 months of life, with peak incidence between 3 months to 5 years 1, 2
Why Other Options Are Not the Hallmark
Option A (Rigid, board-like abdomen): This finding suggests peritonitis from perforation, which is a late complication rather than a hallmark presenting sign 2.
Option B (Vomiting green bile): While bilious vomiting can occur with intussusception as obstruction progresses, it is not the hallmark sign and occurs later in the disease course 3, 2. Nonbilious emesis is actually more common initially 2.
Option D (Sausage-shaped mass in lower left quadrant): While a palpable sausage-shaped abdominal mass is part of the classic triad, it is found in only a minority of cases and is not consistently present 2, 4. The location is also typically in the right upper quadrant, not the left lower quadrant 4.
The Classic Triad (Rarely Complete)
The traditional triad of intussusception includes 2, 5:
- Intermittent abdominal pain (most common)
- Currant jelly stools (bloody stools - occurs later)
- Sausage-shaped abdominal mass (inconsistently present)
However, this complete triad is uncommon in actual clinical practice 2. The intermittent crying with knee drawing remains the most consistent early finding.
Critical Atypical Presentations
Lethargy should be considered a fifth cardinal symptom and may be a significant presenting feature, especially in younger infants who cannot communicate pain effectively 5. Altered mental status can occur even without obvious abdominal findings 2, 5.