A 35-year-old man from Mumbai with a 3-year history of Crohn disease (currently on azathioprine) presents with acute onset of severe abdominal pain, fever (38.5°C), and abdominal distension. On examination, the abdomen is rigid with rebound tenderness in the right lower quadrant. Bowel sounds are absent. Laboratory findings: WBC 16,000/μL, hemoglobin 8.5 g/dL, albumin 2.8 g/dL. CT abdomen shows a dilated small bowel loop with wall thickening and free air under the diaphragm. What is the most likely acute complication?

Question

Accepted Answer

A. Perforation with peritonitis. ## Diagnosis: Perforation with Peritonitis

### Clinical Presentation of Perforation

**Key Point:** The presence of free air under the diaphragm is pathognomonic for bowel perforation and is the most critical finding in this case.

### Clinical Features Supporting Perforation

| Finding | Significance |
|---------|-------------|
| **Acute severe abdominal pain** | Peritoneal irritation from leaked bowel contents |
| **Rigid abdomen with rebound tenderness** | Peritonitis (acute inflammation of peritoneum) |
| **Fever (38.5°C)** | Systemic inflammatory response to bacterial translocation |
| **Absent bowel sounds** | Ileus secondary to peritonitis |
| **Free air under diaphragm (CT)** | **Diagnostic of perforation** |
| **Elevated WBC (16,000)** | Acute bacterial infection |
| **Low albumin (2.8)** | Chronic malnutrition from IBD |

### Pathophysiology of Perforation in Crohn Disease

```mermaid
flowchart TD
  A[Crohn Disease: Transmural Inflammation]:::outcome --> B[Deep ulceration penetrates muscularis propria]:::action
  B --> C[Fistula formation or perforation]:::decision
  C -->|Fistula| D[Enterocutaneous or enterovesical fistula]:::outcome
  C -->|Perforation| E[Free air + peritonitis]:::urgent
  E --> F[Acute abdomen: rigid, rebound, fever]:::urgent
  F --> G[Surgical emergency: resection required]:::action
```

**High-Yield:** Crohn disease causes **transmural inflammation**, which predisposes to both fistulization and perforation. Ulcerative colitis, being mucosal, rarely perforates except in toxic megacolon.

### Why This Is Perforation, Not Other Complications

**Clinical Pearl:** The **free air under the diaphragm** is the gold standard imaging finding for perforation. This is not present in obstruction, fistula, or uncomplicated toxic megacolon.

### Management
- **Immediate surgical consultation** (exploratory laparotomy)
- **Broad-spectrum antibiotics** (cover gram-negative and anaerobes)
- **Fluid resuscitation** and correction of electrolytes
- **Resection of perforated segment** (usually ileocecal region in Crohn disease)
- **Temporary ileostomy** may be required if extensive disease

**Warning:** Perforation in IBD is a surgical emergency with high mortality if not managed promptly. Medical management alone is contraindicated.

![Inflammatory Bowel Disease diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3000.webp)

Answer

B. Enterocutaneous fistula

Answer

C. Toxic megacolon

Answer

D. Intestinal obstruction without perforation

Explanation

Diagnosis: Perforation with Peritonitis

Clinical Presentation of Perforation

Clinical Features Supporting Perforation

Pathophysiology of Perforation in Crohn Disease

Why This Is Perforation, Not Other Complications

Management

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Finding	Significance
Acute severe abdominal pain	Peritoneal irritation from leaked bowel contents
Rigid abdomen with rebound tenderness	Peritonitis (acute inflammation of peritoneum)
Fever (38.5°C)	Systemic inflammatory response to bacterial translocation
Absent bowel sounds	Ileus secondary to peritonitis
Free air under diaphragm (CT)	Diagnostic of perforation
Elevated WBC (16,000)	Acute bacterial infection
Low albumin (2.8)	Chronic malnutrition from IBD