Built from GI Lecture 28 (LOs 1–4). Close notes. Fill from memory. Reveal only after a genuine attempt.

LO 1

ON EXAM — Crohn (mouth-to-anus, transmural, skip lesions, non-caseating granulomas, cobblestone, strictures/fistulas, terminal ileum, smoking WORSENS) vs UC (rectum+continuous, mucosa/submucosa only, crypt abscesses, toxic megacolon, PSC, smoking PROTECTS)

Crohn vs UC — side-by-side

Feature	Crohn Disease	Ulcerative Colitis
Location
Pattern (continuous/skip?)
Depth of inflammation
Gross: mucosal pattern
Gross: wall thickness
Histology buzzword
Typical stool
Classic complications
Smoking effect
Curative surgery possible?
Th response (Th1 vs Th2)
Classic serology

Crohn gross pathology — 5 buzzword findings

Mucosal surface pattern

Creeping fat

String-sign (on barium study)

Wall thickness

Most common segment

Crohn histology — 4 key findings

Transmural inflammation involves

Granulomas — type

Granuloma presence (% of biopsies)

Crypt architecture distortion

UC gross pathology

Starts at ______ and extends proximally

Pseudopolyps (what are they?)

Backwash ileitis means

Depth of ulcers

UC histology

Classic finding (neutrophil aggregates in crypts)

Chronicity marker on biopsy

Granulomas present?

Extraintestinal manifestations of IBD

Eye (2)

Joint (axial + peripheral)

Skin (2)

Liver — strongest UC association

Kidney (Crohn) — stone type

Biliary (Crohn)

🪤 TRAP: PSC is strongly associated with UC (not Crohn). Oxalate kidney stones are a Crohn issue (fat malabsorption → Ca binds fat → oxalate free to be absorbed).

LO 1

ON EXAM — toxic megacolon, severe UC complications, IBD-associated colon cancer (different from sporadic: dysplasia first, flat not polypoid, p53 early / APC late, biannual surveillance starting 8 years after diagnosis)

Severe UC complications — 4

Toxic megacolon — diameter

Toxic megacolon risk

Fulminant colitis features

Long-term malignancy

IBD-associated colon cancer — vs sporadic

Feature	Sporadic CRC	IBD-associated CRC
Precursor lesion
Gross appearance
Sequence (APC/p53 order)
Multifocal?
Location bias

Surveillance — IBD with long-standing colitis

Start colonoscopy _______ after diagnosis

Interval

If PSC + UC, start when?

Strongest risk factors (3)

When would you offer colectomy?

Refractory / fulminant UC

Toxic megacolon not responding

High-grade dysplasia or CRC

LO 2

ON EXAM — C. difficile pathogenesis (toxins A/B), risk factors (antibiotics + PPIs + hospital), pseudomembranous colitis (volcano lesions), diagnosis (PCR + EIA), treatment (oral vanco/fidaxomicin, NOT metronidazole first-line)

C. difficile microbiology

Organism (gram stain/morphology)

Anaerobic or aerobic?

Spore-forming?

Reason spores matter

Toxins — the real weapons

Toxin A = __________ (enterotoxin)

Toxin B = __________ (cytotoxin, more potent)

Molecular mechanism

Hypervirulent strain

Risk factors

Highest-risk antibiotic class 1

Class 2

Class 3

Class 4

Non-antibiotic med risk

Patient risk

Pseudomembranous colitis

Endoscopic finding

Microscopic "volcano" lesion

Composition of pseudomembrane

Diagnostic testing comparison

Test	What it detects	Sens/Spec profile
Stool PCR (NAAT for tcdB)
Stool GDH antigen
Stool toxin EIA

Treatment

First episode, non-severe

Severe / fulminant

Recurrent (≥2nd)

When to give FMT

⚠️ Metronidazole is NO LONGER first-line for C. diff — use oral vancomycin or fidaxomicin. Stop inciting antibiotic if possible.

LO 3

ON EXAM — false diverticulum vs true, sigmoid predilection, painless lower GI bleed (diverticulosis) vs LLQ pain + fever (diverticulitis), Hinchey classification, NO colonoscopy in acute diverticulitis

True vs false diverticulum

True diverticulum — definition

True diverticulum — examples

False diverticulum — definition

Colonic diverticula are _____ (true/false)

Pathophysiology

Weak point (why vasa recta)

Most common location

Why sigmoid (LaPlace's law)

Low-fiber Western diet — mechanism

Diverticulosis vs diverticulitis

Feature	Diverticulosis	Diverticulitis
Symptoms
Classic presentation
Lab findings
Best imaging
Treatment

Complications

Painless hematochezia source

Perforation → peritonitis

Abscess (Hinchey)

Fistula — most common type

Stricture → obstruction

Hinchey classification

Stage	Description
I
II
III
IV

Management

Uncomplicated (mild)

Complicated (abscess > 4 cm)

Hinchey III/IV

When to do colonoscopy

🪤 TRAP: Do NOT do colonoscopy during acute diverticulitis (perforation risk). Wait 4–6 weeks after recovery to rule out cancer.

LO 4

ON EXAM — tubular vs villous adenoma (villous = worst), serrated pathway, APC→KRAS→p53 (CIN) vs MMR/MSI (Lynch), right- vs left-sided CRC, iron-deficiency anemia in older males = CRC until proven otherwise

Polyp classification by malignant potential

Polyp type	Malignant potential	Key feature
Hyperplastic polyp
Tubular adenoma
Tubulovillous adenoma
Villous adenoma
Sessile serrated (SSA/P)
Hamartomatous (juvenile, PJ)

Risk features for malignancy in adenoma

Feature 1 — size

Feature 2 — histology

Feature 3 — dysplasia grade

Villous adenoma — clinical

Classic electrolyte syndrome

Typical symptom

CRC molecular pathways

Pathway	% of sporadic CRC	Mutations (in order)	Classic polyp precursor
Chromosomal instability (CIN)
Microsatellite instability (MSI)

Classic adenoma-carcinoma sequence — mutations

Earliest loss (initiation)

Then (progression)

Then (malignant conversion)

Late (metastasis)

Right-sided vs left-sided CRC

Feature	Right (ascending/cecum)	Left (descending/sigmoid)
Presentation
Growth pattern
Often detected via
Obstruction?

Hereditary CRC syndromes

FAP — gene / inheritance / polyp count

Lynch (HNPCC) — gene family / pattern

Lynch extracolonic cancers (top 2)

Peutz-Jeghers — gene / findings

CRC screening basics

Average-risk start age (USPSTF)

Colonoscopy interval

FIT test interval

Tumor marker for surveillance

🪤 TRAP: Iron-deficiency anemia in a man > 50 = colon cancer until proven otherwise. Right-sided CRC bleeds occultly; left-sided obstructs early.

LOs 1–4

Q1: Crohn vs UC — histology

A 24-year-old man with chronic RLQ pain, diarrhea, perianal fistula, and iron deficiency undergoes colonoscopy. Terminal ileum biopsy shows transmural lymphoid aggregates and a non-caseating granuloma. Diagnosis?

A) Ulcerative colitis
B) Crohn disease
C) Intestinal TB
D) Behçet disease
E) Ischemic colitis

Correct Answer: B

Crohn disease — terminal ileum involvement, transmural inflammation, fistula, non-caseating granuloma. UC spares the terminal ileum (except backwash ileitis), is mucosa-limited, and never causes granulomas. TB causes caseating granulomas.

Q2: UC complication

A 39-year-old woman with 12-year history of UC presents with fever, severe abdominal distention, and bloody stools. AXR: transverse colon dilated to 8 cm. Which complication?

A) Fistula formation
B) Toxic megacolon
C) Terminal ileitis
D) Diverticulitis
E) Colonic volvulus

Correct Answer: B

Toxic megacolon = colonic dilation > 6 cm + systemic toxicity. Risk of perforation is high. Stop anti-motility agents, aggressive resuscitation, IV corticosteroids; colectomy if failing.

Q3: IBD extraintestinal — PSC

A 32-year-old man with long-standing UC develops pruritus and elevated ALP. MRCP: "beaded" intra- and extra-hepatic bile ducts. Diagnosis and antibody?

A) Primary biliary cholangitis; AMA
B) Primary sclerosing cholangitis; p-ANCA
C) Autoimmune hepatitis; ANA
D) Hepatocellular carcinoma; AFP
E) Cholangiocarcinoma; CA 19-9

Correct Answer: B

PSC — characteristic "onion-skin" fibrosis, beaded ducts on MRCP, strongly associated with UC, positive p-ANCA in ~70%. Increased risk of cholangiocarcinoma.

Q4: C. diff — treatment

A 65-year-old woman 5 days post-op on ceftriaxone develops 10 watery stools/day, WBC 18k, Cr stable. Stool PCR and toxin EIA positive. Best initial treatment?

A) IV metronidazole monotherapy
B) Oral vancomycin OR oral fidaxomicin
C) IV vancomycin
D) Loperamide
E) Rifaximin

Correct Answer: B

Current first-line for non-severe initial C. diff = oral vancomycin OR oral fidaxomicin. Fidaxomicin has lower recurrence. IV vanco does NOT penetrate colonic lumen. Loperamide is contraindicated.

Q5: Diverticulitis management

A 62-year-old woman presents with 3 days of LLQ pain, fever 38.5 °C, WBC 14k. CT: inflamed sigmoid diverticula with small pericolonic abscess (3 cm). Best management?

A) Emergent colectomy
B) Outpatient observation alone
C) IV antibiotics + bowel rest; CT-guided drainage if abscess enlarges
D) Colonoscopy during acute episode
E) Barium enema

Correct Answer: C

Hinchey Ib (pericolonic abscess) → IV antibiotics (cipro + metronidazole or pip-tazo) and bowel rest. Drain abscess if > 4 cm. Colonoscopy is CONTRAINDICATED in acute diverticulitis (perforation risk); do it 4–6 weeks later.

Q6: Villous adenoma

A 68-year-old man has copious watery mucoid diarrhea, K 2.8, and a 4-cm rectal mass. Biopsy: polyp composed of long finger-like projections of dysplastic epithelium. Which lesion carries the HIGHEST risk of malignant transformation?

A) Hyperplastic polyp
B) Tubular adenoma
C) Tubulovillous adenoma
D) Villous adenoma
E) Juvenile polyp

Correct Answer: D

Villous adenoma — highest malignant potential (> 30% when > 4 cm). Can cause secretory/hypokalemic diarrhea (McKittrick-Wheelock syndrome). Hyperplastic polyps have no malignant potential.

Q7: CRC — classic adenoma-carcinoma sequence

Which is the EARLIEST and most common mutation in the classic chromosomal instability pathway of sporadic CRC?

A) KRAS
B) p53
C) APC (tumor suppressor)
D) DCC / SMAD4
E) MLH1/MSH2 (MMR)

Correct Answer: C

APC loss is the earliest event (initiation → small adenoma). Sequence: APC → KRAS → p53. MMR mutations (MLH1/MSH2) define the Lynch/MSI pathway (serrated precursor or Lynch syndrome).

Q8: Right-sided CRC presentation

A 72-year-old man presents with fatigue; labs: Hgb 8.2, MCV 72, ferritin 9. No overt GI bleeding. Most likely diagnosis/location?

A) Left-sided CRC, obstructing
B) Right-sided CRC (occult GI bleed, iron-deficiency anemia)
C) Gastric ulcer
D) Hemorrhoids
E) Diverticular bleed

Correct Answer: B

Right-sided CRC typically presents with iron-deficiency anemia from chronic occult bleeding; the wide cecal lumen tolerates bulky exophytic ("fungating") growth without obstruction. Left-sided CRC tends to obstruct (napkin-ring) and present with change in bowel habits.

Q9: Lynch syndrome

A 45-year-old woman has colon cancer; her mother had endometrial cancer at 48 and her uncle had a right-sided colon cancer at 52. Germline testing shows a pathogenic MSH2 mutation. Which additional cancer is she most at risk for?

A) Osteosarcoma
B) Endometrial and ovarian cancer
C) Medullary thyroid cancer
D) Pheochromocytoma
E) Glioblastoma

Correct Answer: B

Lynch syndrome (HNPCC) — autosomal dominant MMR gene mutation (MLH1, MSH2, MSH6, PMS2). Endometrial cancer is the 2nd most common after colon cancer (lifetime risk up to 60%). Also ovarian, gastric, small bowel, urothelial.

Q10: IBD surveillance

A 35-year-old woman with 8-year history of pancolitis UC and newly diagnosed PSC asks about colon cancer screening. What is the recommended strategy?

A) FIT every year starting now
B) Colonoscopy every 10 years starting at age 50
C) Surveillance colonoscopy now and every 1–2 years thereafter
D) CT colonography every 5 years
E) No additional screening needed

Correct Answer: C

Surveillance colonoscopy every 1–2 years after 8 years of pancolitis (or 15 years of left-sided colitis). If PSC is present, start surveillance at the time of PSC diagnosis and continue annually (highest risk group).

Intestinal Path Case Review — Active Recall