Colorectal and Anorectal Disorders
This domain covers colorectal cancer screening and polyp surveillance, hereditary syndromes, and benign anorectal disease. The exam favors interval decisions and anatomy-based diagnosis.
Screening and polyp surveillance
- Average risk: start colonoscopy at 45 years; options are colonoscopy every 10 years, annual FIT, stool DNA testing or CT colonography every 5 years.
- Adenoma surveillance (US Multi-Society Task Force): 1-2 tubular adenomas under 10 mm, 7-10 years; 3-4 adenomas or any adenoma 10 mm or larger, or villous or high-grade histology, 3-5 years; 5 or more adenomas or any adenoma 10 mm or larger with high-grade dysplasia, 3 years. Complete clearance is assumed.
- Serrated polyps: sessile serrated lesions 10 mm or larger or with dysplasia increase risk; serrated polyposis syndrome requires surveillance intervals of 1-3 years.
Hereditary syndromes
- Lynch syndrome: Amsterdam II or Bethesda criteria, universal tumor testing for mismatch repair deficiency or microsatellite instability, germline confirmation. Colonoscopy every 1-2 years from age 20-25; aspirin may reduce cancer risk.
- Familial adenomatous polyposis: APC mutation, hundreds of polyps; prophylactic colectomy in late teens to early twenties; screen for duodenal adenomas with a side-viewing endoscope.
Anorectal disease
- Hemorrhoids: internal above the dentate line, painless bleeding; grades I-IV. Grade I-II respond to fiber and topical therapy; grade III-IV need rubber band ligation, stapled hemorrhoidopexy or surgery.
- Anal fissure: severe pain with defecation; most heal with fiber and topical nitrates or calcium channel blockers; chronic or recurrent cases managed with botulinum toxin or lateral internal sphincterotomy.
- Perianal abscess: painful swelling with fever; treat with urgent incision and drainage. Fistula-in-ano: describe by Parks classification; Goodsall rule applies to anterior and posterior tracts relative to the dentate line.
- Anal squamous cell carcinoma is HPV-associated; treat with chemoradiotherapy (mitomycin plus 5-fluorouracil) rather than abdominoperineal resection.
Worked example
A 58-year-old has three tubular adenomas of 6, 8 and 12 mm, all completely removed. This is high-risk: the 12 mm adenoma and total count of three place him in the 3-year surveillance group. Document complete clearance and repeat colonoscopy in 3 years.
Traps
- Using a 10-year interval after an advanced adenoma.
- Missing that sessile serrated lesions proximal to the splenic flexure carry disproportionate risk.
- Treating an acute perianal abscess with antibiotics alone.
- Offering surgery first-line for anal squamous carcinoma.