A 58-year-old woman with a history of stage III colorectal cancer (treated with chemotherapy 6 months ago) presents with acute-onset severe abdominal pain, vomiting, and abdominal distension over 12 hours. On examination, she is febrile (38.5°C), tachycardic (110 bpm), and has localized tenderness in the left lower quadrant with guarding. Bowel sounds are absent. Plain abdominal X-ray shows dilated small and large bowel loops with air-fluid levels. CT abdomen with IV contrast shows a transition point at the sigmoid colon with proximal bowel dilation, and there is focal wall thickening and pericolonic stranding at the transition zone. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Malignant Obstruction Due to Recurrent Colorectal Cancer ### Key Clinical Features **Key Point:** A patient with prior colorectal cancer presenting with mechanical obstruction at the site of the original tumor (sigmoid colon) strongly suggests recurrent/residual malignancy causing obstruction. The acute presentation with peritoneal signs (guarding, fever) suggests impending strangulation or perforation. ### Radiological Findings Indicating Malignancy | Finding | Significance | |---------|-------------| | Transition point at sigmoid colon | Matches site of original tumor | | Focal wall thickening at transition | Suggests malignant infiltration | | Pericolonic stranding | Indicates local inflammation/invasion | | Proximal bowel dilation | Obstruction distal to transition point | | Both small and large bowel dilation | Left-sided colonic obstruction | ### Pathophysiology of Malignant Obstruction 1. **Mechanism:** Tumor growth → progressive luminal narrowing → mechanical obstruction 2. **Timing:** Can occur at recurrence (months to years after initial treatment) 3. **Risk:** Chemotherapy does not eliminate all cancer cells; residual/recurrent disease is a known complication 4. **Presentation:** Often acute because the narrowing is fixed and progressive ### Clinical Pearl **Clinical Pearl:** Malignant obstruction accounts for 10–15% of mechanical bowel obstructions overall, but in patients with prior colorectal cancer, recurrence must be the first consideration when obstruction occurs at or near the original tumor site. The presence of fever and peritoneal signs suggests impending perforation or strangulation, which are surgical emergencies. ### High-Yield Facts **High-Yield:** In a patient with prior colorectal cancer, mechanical obstruction at the original tumor site is recurrent malignancy until proven otherwise. CT imaging with contrast showing focal wall thickening and stranding is highly suggestive of malignant infiltration rather than simple adhesions or other benign causes. ### Mnemonic **Mnemonic:** **RECUR** — Recurrent cancer, Exact site of prior tumor, CT shows wall thickening, Urgent presentation with peritoneal signs, Requires surgical evaluation. ### Management Considerations **Tip:** Malignant obstruction typically requires surgical intervention (bypass or resection) rather than conservative management. Palliative approaches (stent placement, bypass) may be considered depending on performance status and extent of disease. Emergency surgery is indicated if there are signs of perforation or strangulation (fever, peritonitis, elevated lactate).