A 68-year-old man with a history of abdominal surgery 10 years ago presents to the emergency department with acute onset colicky abdominal pain, abdominal distension, and vomiting. On examination, he has visible peristaltic waves and a palpable abdominal mass. Plain abdominal radiograph shows multiple dilated small bowel loops with air-fluid levels and a transition point in the pelvis. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with classic signs of **mechanical small bowel obstruction** (SBO): colicky pain, vomiting, distension, visible peristalsis, and radiographic evidence of dilated loops with a transition point. The history of prior abdominal surgery makes adhesions the most likely etiology. However, the presence of a **palpable abdominal mass** is a red-flag finding that raises concern for **closed-loop obstruction or strangulation**, mandating urgent CT evaluation before committing to either conservative management or immediate surgery. ## Why CT Abdomen with IV Contrast is the Best Next Step **Key Point:** A palpable abdominal mass in the setting of SBO is a warning sign for **closed-loop obstruction**, which carries a high risk of strangulation and bowel ischemia. Current guidelines (EAST, WSES) recommend **CT abdomen/pelvis with IV contrast** as the investigation of choice when: - A palpable mass is present - Closed-loop obstruction is suspected - Strangulation cannot be excluded clinically CT provides critical information: 1. **Confirms** the diagnosis and identifies the transition point 2. **Detects strangulation** (bowel wall thickening, pneumatosis, mesenteric edema, lack of enhancement) 3. **Identifies the etiology** (adhesion, hernia, volvulus, malignancy) 4. **Guides surgical planning** if operative intervention is needed **High-Yield:** Plain radiograph alone is insufficient to exclude strangulation. CT has a sensitivity of ~83% and specificity of ~93% for detecting strangulation in SBO (Maglinte et al.; Frager et al.). A palpable mass on examination is an independent predictor of the need for surgery and strangulation risk. Importantly, the patient is NOT described as having peritonitis, hemodynamic instability, or frank signs of bowel necrosis — thus immediate laparotomy without CT is premature. **Clinical Pearl:** Conservative management (Option D) is appropriate for **uncomplicated adhesive SBO** in a hemodynamically stable patient with NO alarming features. However, this patient has a **palpable abdominal mass** — a finding that mandates CT before defaulting to watchful waiting, as it may represent a closed-loop segment requiring urgent surgery. CT will determine whether surgery is needed and guide the operative approach. ## Why Other Options Are Incorrect - **Option A (Immediate laparotomy):** Premature without CT confirmation; strangulation has not been confirmed clinically (no peritonitis, no hemodynamic instability described), and CT will guide whether surgery is truly needed and help plan the approach. Rushing to the OR without imaging risks unnecessary surgery or an inadequately planned procedure. - **Option C (Barium follow-through):** Contraindicated in acute complete SBO; barium can worsen obstruction and is not used in the acute setting. Water-soluble contrast (Gastrografin) may be used therapeutically in adhesive SBO but is not the best next step here. - **Option D (Conservative management):** Appropriate for uncomplicated SBO, but the palpable mass is an alarming feature that must be evaluated with CT first before committing to watchful waiting. [cite: WSES Guidelines for SBO 2017; Sabiston Textbook of Surgery, 20th ed., Ch 45; Harrison's Principles of Internal Medicine, 21st ed.; EAST Practice Management Guidelines for SBO]