A 72-year-old woman from Delhi presents with acute onset severe left lower abdominal pain, abdominal distension, and absolute constipation for 3 days. She has a history of chronic constipation and neurological disease (Parkinson's). On examination, she is afebrile, blood pressure 130/80 mmHg, and has mild abdominal tenderness with palpable abdominal mass in the left lower quadrant. Plain abdominal radiograph shows a single massively dilated loop of colon in the left abdomen with a characteristic "bird's beak" appearance at the rectosigmoid junction. What is the most likely radiographic diagnosis?

Explanation

## Clinical Diagnosis: Sigmoid Volvulus ### Pathognomonic Radiographic Signs **High-Yield:** Sigmoid volvulus is diagnosed by the combination of: 1. **Single massively dilated colonic loop** (often >10 cm) 2. **"Coffee bean" or "omega" sign** — the twisted loop appears as a bean or omega shape 3. **"Bird's beak" sign** — abrupt narrowing at the point of torsion (rectosigmoid junction) 4. **Transition zone** — dilated proximal colon to collapsed distal rectum 5. **Absence of haustra** in the dilated loop (due to stretching) ### Risk Factors for Sigmoid Volvulus **Mnemonic: CONSTIPATION** - **C**hronic constipation - **O**lder age (>65 years) - **N**eurological disease (Parkinson's, spinal cord injury, Chagas disease) - **S**edentary lifestyle - **T**rophy of colon (megacolon) - **I**nstitutionalized patients - **P**sychiatric medications (anticholinergics) - **A**bdominopelvic adhesions - **T**ropical regions (endemic in Africa, Middle East, India) - **I**diopathic megacolon - **O**bstruction history - **N**arrow pelvis **Clinical Pearl:** Sigmoid volvulus accounts for 5–10% of large bowel obstructions in Western countries but up to 50% in parts of Africa and India due to dietary factors and chronic constipation. ### Radiographic Comparison: Volvulus Types | Feature | Sigmoid Volvulus | Cecal Volvulus | Toxic Megacolon | |---------|------------------|-----------------|------------------| | **Location** | Left lower abdomen | Right lower abdomen | Diffuse colon | | **Shape** | Coffee bean / omega | Kidney bean | Diffusely dilated | | **Bird's beak** | At rectosigmoid | At ileocecal valve | Absent | | **Haustra** | Absent in dilated loop | Absent in dilated loop | Preserved initially | | **Transition zone** | Sharp, at torsion site | Sharp, at torsion site | Gradual | | **Associated findings** | Chronic constipation | Adhesions, prior surgery | Toxic colitis (IBD, C. difficile) | | **Systemic toxicity** | Mild (unless strangulated) | Mild (unless strangulated) | SEVERE (fever, leukocytosis, sepsis) | ### Management Algorithm for Sigmoid Volvulus ```mermaid flowchart TD A[Sigmoid volvulus on plain film]:::outcome --> B{Signs of strangulation?}:::decision B -->|Yes: fever, peritonitis, elevated lactate| C[Urgent surgery: resection]:::urgent B -->|No: stable patient| D[Attempt decompression]:::action D --> E{Method of decompression}:::decision E -->|Flexible sigmoidoscopy| F[Success in 60-80%]:::action E -->|Rectal tube placement| G[Success in 40-50%]:::action F --> H{Recurrence risk?}:::decision H -->|High| I[Elective sigmoid colectomy]:::action H -->|Low| J[Conservative management]:::action G --> K[If failed: surgical decompression]:::action ``` **Key Point:** Flexible sigmoidoscopy with decompression is the first-line treatment for uncomplicated sigmoid volvulus (success rate 60–80%). However, recurrence occurs in 40–50% of cases, so elective sigmoid colectomy is recommended after successful decompression, especially in elderly patients with recurrent episodes. ### Why "Bird's Beak" is Pathognomonic The "bird's beak" sign represents the **point of torsion** where the sigmoid colon twists on its mesentery. At this site: - The bowel wall is compressed by the twisted mesentery - Abrupt transition from dilated proximal to collapsed distal bowel - On contrast enema, appears as a sharp, tapered narrowing (not gradual like in stricture) **Warning:** Do NOT confuse sigmoid volvulus with toxic megacolon. Toxic megacolon occurs in the context of severe colitis (ulcerative colitis, Crohn's disease, C. difficile infection) and presents with systemic toxicity (fever, sepsis), whereas sigmoid volvulus in an uncomplicated case is often afebrile.