Lower GI — 5-min cram sheet

Lower GI — 5-min cram sheet

_Built from the lower-gi disease index. Deck-faithful._

Buzzword → answer (the vignette reflex)

• Pseudopolyps / lead-pipe colon on barium (loss of haustration) → Ulcerative Colitis
• Backwash ileitis (≤ 25 cm of ileocaecal valve) → Ulcerative Colitis
• Skip lesions + cobblestone + string sign on barium + creeping fat → Crohn's Disease
• Non-caseating sarcoid-like granulomas / transmural inflammation → Crohn's Disease
• pANCA positive → UC (over CD); ASCA positive, pANCA negative → CD
• Colon "carpeted" with hundreds–thousands of polyps, APC on 5q21 → FAP
• Right colon/proximal, mucinous, lymphocytic infiltrate, MSI-H, younger age → Lynch (HNPCC)
• Mucocutaneous pigmentation (lips/buccal/palms/soles) + arborising smooth-muscle-core hamartoma → Peutz-Jeghers
• Scalloping of the liver capsule on CT → Pseudomyxoma Peritonei (pathognomonic)
• Cannonball hepatic nodules / apple-core sign on barium enema → Colorectal Cancer
• Kulchitsky cells of crypts of Lieberkühn, at the tip of the appendix → Appendiceal Carcinoid
• Periumbilical pain migrating to RIF / McBurney's point → Acute Appendicitis
• Painless bright-red bleeding, dripping/squirting on defecation → Internal Haemorrhoids
• Posterior-midline linear ulcer, "more pain, less bleeding" + sentinel pile → Anal Fissure
• Midline pits ~5 cm posterior to anus + protruding hairs ("jeep disease") → Pilonidal Sinus
• Painless bleeding + currant-jelly stool in a child, Tc-99m pertechnetate scan → Meckel's Diverticulum
• Saint's triad = diverticulosis + hiatus hernia + gallstones → Diverticular Disease

Endoscopy / histology / imaging → diagnosis

Criteria / staging / scores at a glance

• Truelove & Witts (severe UC): > 6 stools/day + blood +++, fever > 37.5 °C, HR > 90, ESR > 30 mm/hr, Hb < 10 g/dL, albumin < 30 g/L. (Mild < 4/day, Moderate 4–6, Severe > 6.)
• Massive LGIB: ≥ 4 U blood/24 h, instability + shock, Hb ≤ 6 g/dL, bleeding > 3 days, rebleed within 1 week.
• UC definitive path: diffuse, continuous from rectum, no skip lesions, no deep fissures, no transmural sinus tracts/granulomas.
• CD definitive path: terminal-ileum inflammation, fistulas/sinus tracts, serositis, fat-wrapping, transmural lymphoid aggregates, non-necrotising granulomas, skip lesions, linear ulcers, cobblestone.
• Hinchey (complicated diverticulitis): I pericolic/mesenteric abscess · II pelvic/retroperitoneal abscess · III purulent peritonitis · IV faecal peritonitis. (I–II → drainage; III–IV → surgery.)
• Internal haemorrhoid grades: I enlarged, no prolapse (bleeding only) · II prolapse reduces spontaneously · III needs manual reduction · IV irreducible.
• Parks (anal fistula): 1 Intersphincteric (commonest) · 2 Transsphincteric (2nd) · 3 Suprasphincteric · 4 Extrasphincteric (NOT cryptoglandular).
• St James's MRI (anal fistula): 0 normal · 1 simple intersphincteric · 2 intersphincteric + abscess/track · 3 transsphincteric · 4 transsphincteric + abscess/track in ischiorectal fossa · 5 supralevator/translevator.
• Goodsall's rule: anterior to transverse anal line → straight radial tract; posterior → curved, opens midline posteriorly. Exceptions (complex): anterior openings > 3 cm from margin, or multiple openings.
• Montreal — UC extent: E1 proctitis · E2 left-sided (to splenic flexure) · E3 extensive/pancolitis. CD: Age A1 ≤ 16, A2 17–40, A3 > 40 · Location L1 terminal ileum, L2 colon, L3 ileocolon, L4 upper GI · Behaviour B1 non-stricturing/non-penetrating, B2 stricturing, B3 penetrating, "p" = perianal.
• Toxic megacolon: colon > 5.5 cm (X-ray > 5 cm, thin-walled gas-filled with mucosal islands); transverse colon; mortality 15–25%; urgent subtotal colectomy + Brooke if not resolved in 48 h.
• TNM (CRC) — T: Tis in situ · T1 submucosa · T2 muscularis propria · T3 subserosa · T4 visceral peritoneum. N: N0 none · N1 1–3 nodes (N1a 1, N1b 2–3, N1c tumour deposits, no +ve nodes) · N2 ≥ 4 (N2a 4–6, N2b ≥ 7) · N3 high-tie nodes. M: M1a one organ · M1b > 1 organ/peritoneum.
• pT layers (inner→outer): mucosa → submucosa → muscularis propria → subserosa → peritoneal elastic lamina → mesothelium. pT1 submucosa · pT2 MP · pT3 subserosa · pT4 perforates peritoneum.
• Stage grouping: 0 Tis (polyp removal) · I T1/T2 N0 (surgery) · IIA T3N0, IIB T4aN0, IIC T4bN0 (surgery) · III any node+ (surgery + adjuvant chemo) · IVA M1a, IVB M1b (chemo + biologics ± rectal RT).
• Modified Dukes' + 5-yr survival: A (T1N0) 95% · B1 (T2N0) ~85% · B2 (T3/T4N0, through MP) 80% · C1 (node+, apical node −) ~60% · C2 (apical node +) ~30% · D (M1) 5%.
• Rectal cancer by TNM: T1N0 → local excision; T1–2N0 → transabdominal; T3N0 or any T + N1/N2 → pre-op chemoradiotherapy → surgery.
• Anterior resection by height (from anal verge): ~11–15 cm (upper 3rd, above peritoneal reflection) → AR · ~7–11 cm (middle) → LAR · < 7 cm (lower, pelvic floor) → ULAR.
• Colonic resection by site: caecum/ascending → right hemicolectomy · hepatic flexure → extended right · splenic flexure → extended left · descending → left hemicolectomy · sigmoid → sigmoidectomy. Marginal safe zone = 2 cm.
• Rectal margins: Distal (DRM) + Circumferential (CRM).
• Adenoma malignant potential (highest→lowest): high-grade dysplasia > villous architecture > size (> 2 cm) > multiple. (74% of adenomas < 1 cm → 1% invasive cancer; 35% of adenomas > 2 cm show malignant change.)
• ACG family-history screening: single 1st-degree dx ≥ 60 yr → colonoscopy every 10 yr from age 45; single 1st-degree < 60 yr OR ≥ 2 relatives → age 40 (or 10 yr before youngest's dx), repeat every 5 yr.
• UK National Screening: age 50–74 offered FIT; positive → colonoscopy; negative → repeat every 2 yr.
• Average-risk screening: start FOBT (gFOBT guaiac needs 3-day red-meat elimination, vit C < 250 mg/day, no NSAIDs 7 days; FIT uses antibodies to human Hb, no diet restriction, very good sensitivity; annual US / 2-yearly UK / 3-yearly Holland); starts age 50 or 60.
• Anal cancer risk: HPV-16 very high (18/31/33/35 moderate); HIV; tobacco 5-fold; benign anal pathology (fistula/fissure/haemorrhoid) does NOT increase risk.
• Appendiceal perforation risk: extremes of age, immunosuppression, diabetes, previous abdominal surgery.
• Alvarado (MANTRELS, /10): Migratory RIF pain 1 · Anorexia 1 · Nausea/vomiting 1 · Tenderness RIF 2 · Rebound 1 · Elevated temp 1 · Leukocytosis (WBC ≥ 10×10⁹/L) 2 · Shift to left 1. → < 3 low (discharge/observe); 4–6 imaging; ≥ 7 appendicectomy.
• Pediatric Appendicitis Score (PAS, /10): RLQ tenderness 2 · cough/hopping/percussion RLQ 2 · all others 1. → 1–3 negative; 4–7 further testing; 8–10 positive.
• AIR score: adds CRP to WBC/neutrophilia; better than Alvarado in adults.
• ATLS shock class: I < 750 mL / < 15% / HR < 100 · II 750–1500 / 15–30% / HR > 100 (orthostatic) · III 1500–2000 / 30–40% / HR > 120 (reduced SBP, UO 10–20) · IV > 2000 / > 40% / HR > 140 (supine hypotension, UO < 10).
• Ileal pouch configs: J (2 loops, most popular, linear stapler) · S (3 loops, long spout → evacuation difficulty) · W (4 loops, larger reservoir → less frequency). Pouch 10–20 cm.
• Ileostomy: end Brooke's spout ≥ 4 cm above skin, acts in 48 h; Kock = 30 cm reservoir, emptied by catheter.
• Nigro regime (anal SCC): 5-FU + mitomycin (or 5-FU + cisplatin) + RT; obvious residual → APR.
• APR indications: tumour involves pelvic floor / external sphincter, poorly-differentiated low rectal cancer, or < 1 cm from dentate line.
• Vogelgram (sporadic adenoma-carcinoma): APC/MCC loss → K-ras → DCC loss → p53 loss → carcinoma. (APC/MCC/DCC/p53 = tumour suppressors; K-ras = oncogene.)
• UC surgery indications (emergency): acute severe colitis failing IV steroids, toxic megacolon/impending perforation, perforation, massive haemorrhage, total obstruction from stricture.

Discriminators that decide questions

1. UC vs Crohn's — UC: mucosa + submucosa only, diffuse/continuous from rectum, pseudopolyps, lead-pipe colon, crypt abscesses, resection curative. Crohn's: transmural, segmental skip lesions, cobblestones/string sign, deep fissures + fistulas + granulomas, perianal disease, resection recurrence common.
2. FAP ("gatekeeper") vs HNPCC/Lynch ("caretaker") — FAP: APC (5q21), adenoma-carcinoma sequence, thousands of typical tubular/villous adenomas, 100% cancer by 40–45. HNPCC: MSH2/MLH1 (MMR → MSI), fewer often-sessile polyps, mucinous adenocarcinoma + lymphocytic infiltrate, right colon/younger.
3. Right- vs left-sided diverticula — Right: Asian, congenital, true (all layers), solitary. Left: Western, acquired, false (pseudodiverticula, pulsion), multiple; sigmoid highest pressure (up to 90 mmHg, 9× normal).
4. Internal vs external haemorrhoids — Internal: above dentate line, transitional + columnar epithelium, painless bright-red bleed. External: below dentate line, squamous epithelium, thrombosed = painful throbbing mass.
5. Blood–stool relation localises the source — mixed with faeces → proximal to sigmoid; on surface of faeces → rectum/anal canal; on toilet paper → anal-skin (fissure, external haemorrhoids); separate from faeces (± mucus, urge to defecate) → rectal cancer, diverticular disease, UC, polyp. (↑ urea:creatinine ratio hints UGIB.)