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?

Explanation

## 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.