✅ Model Answer:
• String sign – long, narrow stricture in the terminal ileum (fibrostenotic).
• Skip lesions – areas of normal bowel interspersed with diseased segments.
• Cobblestoning – thickened, nodular mucosa with deep fissures.
• Fistulas – abnormal connections (enterocutaneous, enteroenteric).
• Diagnosis: Crohn disease (ileal stricturing phenotype – Montreal B2).

✅ Model Answer:
• String sign: A long, narrow, thread-like column of barium passing through a strictured segment of bowel.
• Mechanism: Transmural inflammation → fibrosis → luminal narrowing → stricture.
• Location: Most commonly in the terminal ileum (though can occur anywhere).
• Significance: Indicates a fibrostenotic stricture – a complication of Crohn disease (Montreal B2 phenotype).
• Clinical correlation: Presents with obstructive symptoms (crampy abdominal pain, nausea, vomiting, distention).
• Management: Requires endoscopic balloon dilation or surgical strictureplasty/resection.

✅ Model Answer:
• Skip lesions: Areas of normal bowel mucosa interspersed with areas of diseased, inflamed mucosa.
• Significance: This discontinuous pattern of involvement is a hallmark of Crohn disease (unlike ulcerative colitis, which is continuous from the rectum proximally).
• Pathophysiology: Transmural inflammation affects patches of bowel, leaving intervening segments unaffected.
• Location: Can involve any part of the GI tract (mouth to anus).
• Clinical: May present with symptoms from each affected segment (diarrhea, pain, bleeding).

✅ Model Answer:
• Cobblestoning: A radiographic appearance of the mucosa with raised, nodular islands of mucosa separated by deep, linear ulcers/fissures.
• Mechanism: Transmural inflammation causes submucosal edema and fibrosis → mucosa becomes thickened and raised. Deep fissuring ulcers between these islands create the cobblestone appearance.
• Significance: Highly characteristic of Crohn disease.
• Appearance on barium study: Irregular, nodular filling defects with barium tracking into deep fissures.
• Associated with: Stricturing and penetrating disease.

✅ Model Answer:
• Gastrointestinal: Chronic diarrhea (may be bloody), abdominal pain (often right lower quadrant), nausea, vomiting, anorexia.
• Growth: Failure to thrive, weight loss, delayed puberty, short stature.
• Systemic: Fatigue, fever, malaise.
• Extraintestinal: Perianal disease (fistulas, abscesses, skin tags), oral aphthous ulcers, erythema nodosum, pyoderma gangrenosum, arthritis, uveitis, primary sclerosing cholangitis.
• Examination: Abdominal tenderness, palpable mass (thickened bowel), perianal fistula/fissure.
• Laboratory: Anemia, elevated CRP/ESR, hypoalbuminemia, elevated fecal calprotectin.

✅ Model Answer:
• Paris classification is used to phenotype pediatric IBD:
- A: Age at diagnosis (A1a: <10 years; A1b: 10-17 years; A2: 17-40 years).
- L: Location (L1: ileal; L2: colonic; L3: ileocolonic; L4a: upper GI proximal to ligament of Treitz; L4b: upper GI distal to ligament of Treitz).
- B: Behavior (B1: non-stricturing, non-penetrating; B2: stricturing; B3: penetrating).
- p: Perianal disease modifier (p: if present).
• Example: This patient (terminal ileal stricture, perianal fistula) = A1b, L1, B2p.

✅ Model Answer:
• Diagnosis: To detect and characterize small bowel involvement (which is common in Crohn).
• Assessment of extent and severity: To identify skip lesions, strictures, fistulas, and mucosal disease.
• Differentiation from ulcerative colitis: Small bowel involvement is the key differentiator (UC is limited to the colon).
• Pre-operative planning: To define the anatomy before surgical resection.
• Monitoring: To assess response to therapy or detect complications.
• Modalities: MR enterography (preferred, no radiation), CT enterography, small bowel follow-through (barium), capsule endoscopy.

✅ Model Answer:
• Medical therapy (for inflammatory strictures):
- Exclusive enteral nutrition (EEN) – 6-8 weeks (reduces inflammation).
- Corticosteroids (prednisone) – short-term for acute inflammation.
- Biologics (anti-TNF: infliximab, adalimumab) – can reduce inflammation and prevent progression.
- Immunomodulators (azathioprine, methotrexate).
• Endoscopic therapy:
- Balloon dilation – for short, non-fibrotic strictures (<5 cm).
• Surgical therapy (for fibrostenotic strictures):
- Strictureplasty (Heineke-Mikulicz, Finney) – for multiple strictures.
- Segmental resection (ileocecectomy) – for isolated terminal ileal stricture.
- Laparoscopic approach is preferred.

✅ Model Answer:
• Musculoskeletal: Peripheral arthritis (Type I – pauciarticular, associated with colonic disease), axial arthritis (ankylosing spondylitis, sacroiliitis).
• Dermatologic: Erythema nodosum (painful nodules on shins), pyoderma gangrenosum (ulcerative lesions), oral aphthous ulcers.
• Ocular: Uveitis (anterior), episcleritis.
• Hepatobiliary: Primary sclerosing cholangitis (PSC), fatty liver, gallstones.
• Renal: Nephrolithiasis (oxalate stones), obstructive uropathy.
• Growth: Failure to thrive, delayed puberty, short stature.
• Perianal: Fistulas, abscesses, fissures, skin tags.
• Vascular: Thromboembolism, vasculitis.

✅ Model Answer:
• This is a fibrostenotic stricture causing partial obstruction.
• Next steps:
1. Assess severity: Clinical exam, abdominal X-ray (obstruction series).
2. If partial obstruction: NPO, IV fluids, NG tube decompression.
3. Evaluate for surgical intervention:
- If fibrotic (string sign on imaging, no response to medical therapy) → surgery is indicated.
- Options: Strictureplasty (if multiple strictures) or ileocecal resection.
4. If medical therapy is still appropriate: Trial of exclusive enteral nutrition (EEN) or biologic therapy (infliximab) to reduce inflammation (if not purely fibrotic).
5. Referral to pediatric gastroenterology and pediatric surgery.

✅ Model Answer:
• MR enterography:
- Preferred modality in children (no ionizing radiation).
- Assesses mural thickening, strictures, fistulas, and extramural complications (abscesses).
- Can evaluate the entire small bowel.
- Provides functional information (peristalsis, contrast enhancement).
- Excellent for monitoring disease activity.
• Barium studies (small bowel follow-through):
- Higher radiation exposure (now less commonly used).
- Excellent luminal detail (mucosal pattern, strictures, fistulas).
- Limited in assessing extramural disease (abscesses).
• Current practice: MR enterography is the preferred first-line imaging for pediatric Crohn disease.

✅ Model Answer:
• Perianal fistula is a penetrating complication of Crohn disease (Montreal B3p).
• Management:
1. Medical:
- Anti-TNF therapy (infliximab or adalimumab) – first-line for perianal fistulizing Crohn disease.
- Immunomodulators (azathioprine, methotrexate) – used in combination with anti-TNF.
- Metronidazole or ciprofloxacin – for acute infection/abscess (adjunctive).
2. Surgical:
- Seton placement – for drainage of acute abscess.
- Fistulotomy – for low simple fistulas.
- Advancement flap – for complex fistulas.
3. Multidisciplinary: Gastroenterology + colorectal surgery + radiology (MRI pelvis for assessment).