What is the cause of acquired intestinal obstruction in a 5-year-old child presenting with abdominal distension, stenosis, and a gush of liquid and stool on physical examination (PR)?

Acquired Hirschsprung Disease (Chagas Disease)

The acquired form of this condition—presenting with abdominal distension, rectal stenosis, and gush of liquid stool on digital rectal examination—is caused by Trypanosoma cruzi (option b), the etiologic agent of Chagas disease.

Clinical Reasoning

This clinical presentation describes Hirschsprung disease or a Hirschsprung-like condition:

• Abdominal distension with stenosis on PR examination followed by a gush of liquid stool is the pathognomonic finding for functional or anatomic distal obstruction 1
• The "gush sign" occurs when the examining finger passes through a stenotic/spastic segment, releasing accumulated proximal contents 1
• In a 5-year-old child, this presentation suggests either congenital Hirschsprung disease presenting late or an acquired megacolon 2, 3

Etiology of Acquired Forms

Congenital Hirschsprung disease results from absent ganglion cells in the myenteric plexus, but the question specifically asks about the acquired type:

Trypanosoma cruzi (Chagas Disease) - The Correct Answer

• T. cruzi causes Chagas disease, which leads to destruction of the myenteric plexus neurons throughout the GI tract 1
• This results in acquired megacolon and megaesophagus with clinical features identical to congenital Hirschsprung disease 1
• The parasitic infection causes chronic denervation, producing functional obstruction with proximal dilation 1
• Endemic in Latin America, but cases occur worldwide due to migration 1

Why Other Options Are Incorrect

• Ascaris (option a): Causes mechanical obstruction from worm bolus, not stenosis with megacolon 1
• T. pallidum (option c): Causes syphilitic strictures but extremely rare in children and doesn't produce this specific presentation 1
• Salmonella (option d): Causes acute gastroenteritis or typhoid fever, not chronic stenosis with megacolon 4

Diagnostic Approach in This Patient

When encountering this presentation, systematically evaluate:

• History: Endemic area exposure (Chagas), previous surgeries (adhesions), chronic constipation since birth (congenital Hirschsprung) 1
• Physical examination: Assess for visible peristalsis, degree of distension, and perform careful digital rectal exam noting sphincter tone and the "gush sign" 1, 5
• Laboratory tests: Complete blood count, electrolytes, and Chagas serologies (T. cruzi IgG) if acquired form suspected 1, 4
• Imaging: Plain radiographs show dilated bowel loops; contrast enema demonstrates transition zone 5, 2
• Definitive diagnosis: Rectal suction biopsy to assess for ganglion cells (absent in both congenital and Chagas-related disease) 2, 3

Critical Pitfalls to Avoid

• Don't dismiss chronic symptoms as simple constipation in a 5-year-old—this warrants investigation for organic pathology 2, 3
• Don't confuse incomplete obstruction with gastroenteritis—the gush of liquid stool after stenosis is obstruction, not diarrhea 5
• Consider geographic history—failure to ask about Latin American exposure may miss Chagas disease 1
• Recognize that congenital Hirschsprung can present late (even at 5 years) if the aganglionic segment is short 2, 3