## Anatomical Distribution of Colorectal Carcinoma **Key Point:** The sigmoid colon and rectum are the most common sites of colorectal carcinoma, accounting for 50–60% of all cases globally and in the Indian population. ### Frequency by Site | Anatomical Site | Frequency (%) | Notes | |---|---|---| | Rectum | 20–25% | Most frequent single site; easier to detect on digital rectal exam | | Sigmoid colon | 25–30% | Second most common; accessible on sigmoidoscopy | | Rectosigmoid junction | 5–10% | Often grouped with rectum and sigmoid | | Descending colon | 10–15% | Less common than left-sided lesions | | Caecum and ascending colon | 15–20% | Right-sided lesions; often present late | | Transverse colon | 5–10% | Uncommon | | Splenic and hepatic flexures | 2–5% | Rare | **High-Yield:** Left-sided lesions (rectum + sigmoid + descending) account for ~60% of colorectal cancers. Right-sided lesions (caecum + ascending) account for ~20%. This distribution is consistent across most populations, including India. ### Clinical Significance of Site **Rectosigmoid Lesions (Most Common):** - Accessible on digital rectal examination and sigmoidoscopy - Present with altered bowel habits, tenesmus, blood in stool - Earlier detection possible due to accessibility - Better prognosis when detected early **Right-Sided Lesions (Caecum/Ascending Colon):** - Wider luminal diameter → lesions grow larger before causing obstruction - Often present at advanced stage (T3/T4) - May present with anemia rather than bleeding - Higher risk of perforation - Worse prognosis due to late presentation **Clinical Pearl:** In India, the distribution mirrors global patterns, with left-sided (rectosigmoid) lesions being more common. However, a shift toward right-sided lesions has been noted in some developed populations, possibly due to screening practices. **Mnemonic: LEFT-SIDED LESIONS ARE COMMON (LSL-AC):** - **L** — Lesions on left side (rectum, sigmoid, descending) are most common - **E** — Earlier detection (accessible, cause symptoms early) - **F** — Frequently present with altered bowel habits and bleeding - **T** — Tenesmus and urgency are common symptoms **S** — Sigmoid and rectum account for >50% of all colorectal cancers - **I** — In India, distribution follows global pattern - **D** — Descending colon is less common than sigmoid - **E** — Early-stage detection is more likely for left-sided lesions - **D** — Distal lesions (right-sided) present late with advanced disease **A** — Ascending colon (right-sided) lesions are less common - **C** — Caecal lesions present with anemia, not bleeding [cite:Robbins 10e Ch 17]
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