## Most Common Site of Large Bowel Obstruction **Key Point:** The sigmoid colon is the most common site of large bowel obstruction, accounting for 40–60% of all colonic obstructions. ### Anatomical Distribution of LBO Sites | Site | Frequency | Common Causes | |------|-----------|----------------| | **Sigmoid colon** | 40–60% | Volvulus, carcinoma, diverticulitis | | Rectum | 10–20% | Carcinoma, stricture | | Descending colon | 10–15% | Carcinoma, adhesions | | Splenic flexure | 5–10% | Carcinoma, rare | | Hepatic flexure | 5% | Carcinoma | | Cecum | 10–15% | Carcinoma, rarely volvulus | ### Why the Sigmoid Colon Is Most Vulnerable 1. **Anatomical narrowing:** The sigmoid has the smallest luminal diameter of the colon, predisposing to obstruction. 2. **Increased intraluminal pressure:** Laplace's law dictates that smaller-diameter segments generate higher wall tension; this favors obstruction and perforation risk. 3. **Redundancy and mobility:** The sigmoid is long and redundant, making it prone to volvulus (twisting). 4. **High prevalence of pathology:** Carcinoma, diverticulitis, and volvulus all preferentially affect the sigmoid. **High-Yield:** Sigmoid volvulus is the most common cause of LBO in **developing countries** (including India); colorectal carcinoma is most common in **developed countries**. Both occur at the sigmoid. ### Clinical Correlation **Mnemonic:** **SCARF** — Sites of Colorectal obstruction (in order of frequency): - **S** — Sigmoid (most common) - **C** — Cecum - **A** — Ascending colon - **R** — Rectum - **F** — Flexures (splenic and hepatic) **Clinical Pearl:** A patient with acute LBO and a history of constipation, straining, or prior episodes of abdominal pain should raise suspicion for sigmoid volvulus, especially in elderly or institutionalized patients.
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