A 42-year-old woman from Delhi presents with acute-onset severe abdominal pain, vomiting, and abdominal distension for 6 hours. She has no prior surgical history. On examination, she is febrile (38.5°C), tachycardic (110 bpm), and has marked abdominal tenderness with guarding. Contrast-enhanced CT abdomen shows a twisted loop of small bowel with a 'whirl' sign, mesenteric edema, and areas of non-enhancing bowel wall. What is the most likely diagnosis?

Explanation

## Imaging Diagnosis: Small Bowel Volvulus with Strangulation **Key Point:** The 'whirl' sign on CT — a twisted mesentery with swirling vessels around the obstruction site — is pathognomonic for volvulus. Combined with signs of strangulation (fever, peritoneal signs, non-enhancing bowel wall), this is a surgical emergency. ### Pathophysiology & Clinical Features **High-Yield:** Volvulus occurs when a loop of bowel twists on its mesentery, causing: 1. **Mechanical obstruction** (luminal narrowing) 2. **Vascular compromise** (mesenteric vessels twisted → ischemia) 3. **Strangulation** (if untreated → transmural necrosis) Unlike adhesions, volvulus presents with: - **Sudden onset** (not gradual) - **Severe pain** (not colicky) - **Signs of peritonitis** (fever, guarding, rebound tenderness) - **Elevated inflammatory markers** (WBC, lactate) ### CT Imaging Features of Volvulus | Feature | Significance | |---------|-------------| | **Whirl sign** | Twisted mesentery with spiral vessels (pathognomonic) | | **Transition zone** | Abrupt narrowing at twist site | | **Mesenteric edema** | Indicates vascular compromise | | **Non-enhancing bowel wall** | Transmural ischemia / strangulation | | **Free fluid** | May indicate perforation or peritonitis | | **Collapsed distal bowel** | Mechanical obstruction | **Clinical Pearl:** The 'whirl' sign is best seen on axial CT images at the level of the twist. Look for the mesenteric vessels spiraling around the obstruction site — this is virtually diagnostic of volvulus. ### Distinguishing Volvulus from Other Obstructions ```mermaid flowchart TD A[Small Bowel Obstruction]:::outcome --> B{Imaging findings?}:::decision B -->|Whirl sign + twisted mesentery| C[Volvulus]:::action B -->|Stepladder pattern + no transition| D[Adhesion]:::action B -->|Target sign + intussusceptum| E[Intussusception]:::action C --> F{Signs of strangulation?}:::decision F -->|Yes: fever, peritonitis, non-enhancing wall| G[Strangulation - URGENT SURGERY]:::urgent F -->|No: stable vitals, enhancing wall| H[Simple volvulus - Elective surgery]:::action ``` **Mnemonic: VOLVULUS Red Flags** - **V**isceral ischemia (non-enhancing bowel) - **O**nset sudden (not gradual) - **L**oop twisted (whirl sign) - **V**ascular compromise (mesenteric edema) - **U**rgent surgery needed - **L**oss of bowel wall enhancement - **U**nstable vitals (fever, tachycardia) - **S**trangulation signs (peritonitis) ### Why Surgery is Urgent Strangulation (evidenced by non-enhancing bowel wall and peritoneal signs) means: - Transmural necrosis is occurring - Risk of perforation and sepsis - Mortality increases significantly if surgery delayed >6 hours - **Operative management**: detorsion ± resection of necrotic segment **High-Yield:** Non-enhancing bowel wall on contrast-enhanced CT is the most specific imaging sign of strangulation and mandates immediate surgical intervention. [cite:Harrison 21e Ch 297; Robbins 10e Ch 17]