A 72-year-old woman with no prior abdominal surgery presents with progressive abdominal distension, constipation, and colicky pain for 5 days. On examination, she is afebrile but tachycardic (HR 110/min), abdomen is massively distended with absent bowel sounds. Plain abdominal X-ray shows a hugely dilated colon (diameter 12 cm) with a transition zone at the rectosigmoid junction and no small bowel dilatation. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Analysis This patient presents with **acute colonic obstruction** with the following features: - No prior abdominal surgery (rules out adhesions as primary cause) - Progressive distension, constipation, colicky pain over 5 days - Massively dilated colon (12 cm — far exceeds normal 5–6 cm) - Transition zone at rectosigmoid (suggests distal obstruction) - Absent bowel sounds (suggests ileus or complete obstruction) - Tachycardia (sign of physiological stress) ## Differential Diagnosis of Colonic Obstruction | Cause | Frequency | Age | Presentation | Key Features | |-------|-----------|-----|--------------|---------------| | **Colorectal cancer** | 60% | > 50 years | Progressive, left-sided | Transition zone, no prior surgery | | **Sigmoid volvulus** | 10–15% | Elderly | Acute, recurrent | "Bird's beak" on imaging | | **Diverticulitis** | 10% | > 50 years | Fever, LLQ pain | Pericolonic inflammation | | **Adhesions** | 5% | Prior surgery | Acute or subacute | History of laparotomy | | **Ischemic colitis** | 5% | Elderly, cardiac disease | Bloody diarrhoea + pain | Segmental involvement | ## Management Algorithm for Acute Colonic Obstruction ```mermaid flowchart TD A[Acute colonic obstruction]:::outcome --> B{Signs of perforation?}:::decision B -->|Yes: fever, peritonitis, free air| C[Emergency surgery]:::urgent B -->|No| D[CT abdomen + IV contrast]:::action D --> E{Cause identified?}:::decision E -->|Cancer / volvulus / stricture| F[Therapeutic intervention]:::action F --> G{Resectable?}:::decision G -->|Yes| H[Surgical resection]:::action G -->|No| I[Stent or colostomy]:::action E -->|Pseudo-obstruction / Ogilvie| J[Conservative management + neostigmine]:::action D --> K{Perforation on CT?}:::decision K -->|Yes| L[Emergency laparotomy]:::urgent K -->|No| M[Proceed with definitive management]:::action ``` ## High-Yield: **CT abdomen with IV contrast is the gold standard next step** because it: 1. **Identifies the cause** — cancer, volvulus, diverticulitis, stricture, ischemia 2. **Assesses for perforation** — free air, abscess, peritoneal signs 3. **Evaluates tumour resectability** — staging (if malignancy) 4. **Guides therapeutic strategy** — surgery vs. endoscopic stenting vs. conservative management ## Key Point: **In colonic obstruction without prior surgery, malignancy must be ruled out.** A transition zone at the rectosigmoid in an elderly patient is highly suspicious for colorectal cancer. CT is essential to confirm the diagnosis and stage the disease before any intervention. ## Clinical Pearl: The **absence of small bowel dilatation** rules out small bowel obstruction and confirms the obstruction is at or distal to the ileocaecal valve. The **massive colonic dilatation (12 cm)** indicates significant obstruction and risk of caecal perforation (caecal diameter > 12 cm has high perforation risk). ## Warning: ~~Rectal tube insertion~~ alone is inadequate because it does not address the underlying cause (likely cancer) and delays diagnosis. ~~Nasogastric tube and observation~~ is inappropriate because the obstruction is colonic (NGT decompresses small bowel only) and the patient needs urgent diagnosis to prevent perforation. [cite:Sabiston Textbook of Surgery 21e Ch 46; Harrison 21e Ch 298]