Colonoscopy: What Is Examined, What Is Found, and Why It Matters

Colonoscopy examines the entire large intestine (colon) and rectum using a flexible, lighted colonoscope with a camera. It is the gold standard for colorectal cancer (CRC) screening and diagnosis.

Anatomy Visualized

• Rectum (12–15 cm)
• Sigmoid colon
• Descending colon
• Splenic flexure
• Transverse colon
• Hepatic flexure
• Ascending colon
• Cecum (landmarks: ileocecal valve, appendiceal orifice)
• Terminal ileum (intubated in ~95% for complete exam)

Findings and Interventions

• Polyps: Adenomatous (tubular, villous, tubulovillous) — precancerous; removed by polypectomy (snare, cold forceps). Serrated polyps (SSL, TSA) — also precancerous.
• Cancer: Biopsied; tattooed for surgical localization.
• Inflammation: Ulcerative colitis, Crohn’s colitis, infectious, ischemic, diversion.
• Diverticulosis: Colonic outpouchings; bleeding source.
• Angioectasias: Vascular lesions; bleeding.
• Hemorrhoids: Internal (graded I–IV); banding possible during scope.

Quality Metrics

• Cecal intubation rate >95% (screening).
• Adenoma detection rate (ADR) ≥25% (men), ≥15% (women) — key quality indicator.
• Withdrawal time ≥6 minutes (careful inspection).
• Bowel prep adequacy (Boston Bowel Prep Scale ≥2 per segment).

Screening Guidelines (US)

• Average risk: start at 45 (USPSTF, ACS); options: colonoscopy q10y, FIT annually, Cologuard q3y, CT colonography q5y, flexible sig q5y.
• Higher risk (family history, IBD, genetic syndromes): earlier, more frequent.

Colonoscopy prevents CRC by detecting and removing adenomas before malignant transformation.