Lectures 19–20: Intestinal Pathology I & II
HoyaDocs — GI Block | USMLE Step 1 Preparation
Lectures 19–20 — Overview
Intestinal Pathology I & II · HoyaDocs GI Block
Page Summaries
True vs. pseudo diverticula · Meckel diverticulum (Rule of 2's) · Hirschsprung disease (RET mutation)
Practice Qs: Q1–Q3
Hernia · Adhesions · Volvulus · Intussusception · Ischemic complications
Practice Qs: Q4–Q6
Thrombosis vs. embolism · Watershed areas · Patchy hemorrhagic mucosa · Bloody diarrhea
Practice Qs: Q7–Q9
4 phases of absorption · Diarrhea types · Celiac: HLA-DQ2/DQ8 · Villous atrophy · Gluten-free diet
Practice Qs: Q10–Q12
Crohn (skip lesions, transmural, granulomas) · UC (continuous, mucosa only, crypt abscesses) · Cancer risk
Practice Qs: Q13–Q16
Pseudo-diverticula · Sigmoid colon · Low-fiber diet · Diverticulitis complications
Practice Qs: Q17–Q18
Nonneoplastic vs. neoplastic · Hyperplastic · Hamartomatous syndromes (Peutz-Jegher, Juvenile) · Tubular adenoma
Practice Qs: Q19–Q22
APC/b-catenin pathway · MSI pathway · FAP · Lynch syndrome · Anal canal tumors
Practice Qs: Q23–Q26
Official Learning Objectives Map
LO 1 — Congenital Anomalies & Diverticula
Meckel Diverticulum · Hirschsprung Disease · HoyaDocs GI Block
- LO 1a: Distinguish between congenital and acquired diverticula of the small intestine
- LO 1b: Characterize the pathogenesis of Meckel diverticulum, potential complications, and clinical implications
- LO 1c: Characterize the pathogenesis of Hirschsprung disease and describe its clinical and pathologic features
▼ True vs. Pseudo Diverticula
⭐ A diverticulum is a pouch-like outpouching of the intestinal wall. The distinction between true and pseudo comes down to which layers are involved.
📌 Classification
| Feature | True Diverticulum | Pseudo (False) Diverticulum |
|---|---|---|
| Wall layers | All 3 layers (mucosa, submucosa, muscularis) | Mucosa and submucosa only |
| Origin | Congenital (developmental failure) | Acquired (increased intraluminal pressure) |
| Example | Meckel diverticulum | Colonic diverticulosis (LO 6) |
| Clinical significance | Can contain ectopic gastric/pancreatic tissue | Diverticulitis if inflamed; more common |
🔬 Meckel Diverticulum
Pathogenesis: Failure of the vitelline (omphalomesenteric) duct to regress during fetal development. This duct normally connects the developing gut to the yolk sac and should disappear by week 7 of gestation.
Everything about Meckel comes in 2's:
- 2% of the general population
- Within 2 feet of the ileocecal valve
- 2 inches long
- Symptomatic by age 2
- 2 types of ectopic tissue: gastric and pancreatic
Complications:
- GI bleeding — ectopic gastric mucosa secretes acid → ulceration of adjacent ileum → painless rectal bleeding (most common complication in children)
- Obstruction — can act as a lead point
- Volvulus — intestines can wrap around the diverticulum
- Intussusception — rare lead point for telescoping
- Diverticulitis — inflammation mimics appendicitis
- Meckel scan (technetium-99m pertechnetate) detects ectopic gastric mucosa
- Most common cause of painless lower GI bleed in children <2 years
- Located on the antimesenteric border of the ileum
- Meckel diverticulitis presents with RLQ pain identical to appendicitis. Always consider Meckel in a child presenting with "appendicitis" if the appendix is normal at surgery.
- Meckel is a true diverticulum (all 3 layers) — unlike colonic diverticula which are pseudo-diverticula.
▼ Hirschsprung Disease (Congenital Aganglionic Megacolon)
⭐ Defined as congenital aganglionic megacolon — the name tells you everything: it's congenital, there are no ganglion cells (aganglionic), and it leads to a dilated colon (megacolon).
🔬 Pathogenesis
Failure of neural crest cells to migrate to the wall of the colon → absence of ganglion cells in the myenteric (Auerbach's) and submucosal (Meissner's) plexuses of the affected segment.
- Gene: Loss-of-function mutation in RET (receptor tyrosine kinase) — causes a migration arrest or premature death of ganglion cells. Responsible for most familial cases and ~15% of sporadic cases.
- Result: Aganglionic segment → no peristalsis → functional obstruction → dilation of the innervated segment proximal to the aganglionic zone → megacolon
- Association: Down syndrome (trisomy 21)
🩺 Clinical Features
- Presentation: Failure to pass meconium within 48 hours of birth (first "baby poop") + abdominal distension
- Key anatomic point: The rectum is always affected — the aganglionic segment always begins at the internal anal sphincter and extends proximally for a variable length
- Diagnosis: Histologic confirmation by rectal biopsy (absence of ganglion cells on H&E); the aganglionic region is grossly normal (the dilated part looks diseased but is actually the innervated segment)
| Feature | Details |
|---|---|
| Symptoms | Failure to pass meconium, constipation, abdominal distension |
| Physical exam | Distended abdomen; explosive release of stool on rectal exam |
| Diagnosis | Rectal suction biopsy (absence of ganglion cells) |
| Treatment | Surgical resection of aganglionic segment |
⚠️ Complications
- Enterocolitis — most feared; bacterial overgrowth proximal to the obstruction → inflammatory colitis → potentially fatal
- Perforation — surgical emergency
- Peritonitis — from perforation
- The dilated portion (megacolon) is the normal, innervated segment proximal to the blockage — NOT the aganglionic segment.
- The aganglionic rectosigmoid segment is grossly normal in appearance but functionally obstructed. Biopsy the narrow (aganglionic) zone to confirm diagnosis.
🧠 Testing Your Understanding!
Testing Your Understanding — LO 1, Question 1
A 3-week-old infant presents with abdominal distension and has not passed stool since birth. Rectal examination produces an explosive release of stool and gas. Biopsy of the rectosigmoid region shows absence of ganglion cells. What is the underlying molecular defect, and why does the proximal colon dilate while the rectal biopsy site appears grossly normal?
Consider: neural crest cell migration, RET signaling, which segment is actually obstructed vs. dilated
The RET receptor tyrosine kinase normally guides neural crest cell migration into the bowel wall. Without RET signaling, ganglion cells fail to populate the rectosigmoid (and sometimes more proximal segments). The aganglionic zone has no peristalsis → functional obstruction. The normal innervated colon proximal to the blockage dilates as stool backs up, creating the classic megacolon. The aganglionic segment itself appears grossly normal (hence biopsy is the diagnostic gold standard).
LO 2 — Intestinal Obstruction
Hernia · Adhesions · Volvulus · Intussusception · HoyaDocs GI Block
- LO 2a: List the differential diagnosis for intestinal obstruction and identify risk factors for each type
- LO 2b: Describe the pathologic processes and features; correlate with potential complications (ischemia, infarction)
▼ Overview: Functional vs. Physical Obstruction
⭐ Intestinal obstruction can be functional (e.g., Hirschsprung — no propulsive force) or physical (mechanical barrier). Physical obstructions carry a risk of ischemia/infarction if vascular supply is compromised.
- Functional obstruction: Normal anatomy, but no effective peristalsis (Hirschsprung, ileus)
- Physical obstruction: Mechanical barrier — Hernia, Adhesions, Volvulus, Intussusception
- Key complication: Luminal and/or vascular compromise → ischemia → infarction → perforation → sepsis
▼ Hernia
⭐ A hernia is a weakness or defect in the abdominal wall that allows the intestine (or omentum) to protrude through.
📌 Key Features
- Cause: Weakness/defect in the abdominal wall → bowel loops or omentum herniate through
- Common locations: Inguinal region (most common overall), umbilical, incisional (prior surgery site), femoral
- Risk factors: Prior abdominal incisions, increased intra-abdominal pressure (obesity, pregnancy, coughing), congenital defects
- Critical complication: Incarceration → Strangulation → pressure in the herniated pouch impairs blood flow → ischemia → infarction (surgical emergency)
- Strangulation = compromised blood supply to herniated bowel
- Signs: severe pain, tenderness, non-reducible hernia, signs of bowel obstruction
- Requires urgent surgical repair
▼ Adhesions
⭐ Adhesions are fibrous bands that form between bowel loops and surrounding structures, limiting normal intestinal movement.
📌 Key Features
- Cause: Fibrous connections between bowel loops, abdominal wall, or organs after peritoneal injury
- Risk factors: Prior abdominal surgery (#1 cause), peritoneal infection, endometriosis, inflammatory conditions
- Effect: Restricts normal intestinal movement → kinking → obstruction → risk of ischemia
- Key point: You do NOT need surgery to develop adhesions — any inflammatory process can cause them
- While post-surgical adhesions are most common, they can also form from endometriosis, PID, appendicitis, and other inflammatory conditions. Think beyond OR patients.
▼ Volvulus
⭐ Volvulus is twisting of a loop of bowel around its mesenteric point of attachment — causing both luminal obstruction AND vascular compromise.
📌 Key Features
- Most common site: Sigmoid colon — it hangs by itself and has a relatively loose mesenteric attachment, making it prone to twisting
- Second most common: Cecum
- Effect: Luminal AND vascular compromise → features of obstruction (distension, pain) + infarction if prolonged
- Imaging: Classic "coffee bean" sign on plain radiograph (sigmoid volvulus)
- Treatment: Endoscopic decompression; surgical resection if gangrenous
▼ Intussusception
⭐ Intussusception is the telescoping of a proximal segment of bowel into a distal segment, dragging the mesentery along with it.
📌 Key Features
- Common in: Children (most common cause of bowel obstruction in infants); often idiopathic or following viral illness (Peyer's patch hypertrophy as lead point)
- Most common location: Ileocecal junction (where SI meets LI) — difference in peristaltic waves creates the telescoping
- Lead point in adults: Always suspect a mass (polyp, tumor) acting as lead point in adults — higher malignancy concern
- Effect: Compression of mesenteric vessels → ischemia → potential tissue necrosis
- Classic triad: Colicky abdominal pain + currant-jelly stools (blood + mucus) + palpable "sausage-shaped" mass
- Barium or air enema is both diagnostic AND therapeutic in children
- In adults, always look for a lead point (cancer until proven otherwise)
▼ Comparison Table: Physical Obstructions
| Type | Mechanism | High-Risk Population | Vascular Compromise? | Key Complication |
|---|---|---|---|---|
| Hernia | Bowel protrudes through wall defect | Post-op, obese, elderly | Yes (strangulation) | Strangulation → infarction |
| Adhesions | Fibrous bands restrict movement | Post-surgical (most common cause of SBO) | Possible (kinking) | Small bowel obstruction |
| Volvulus | Bowel twists on mesentery | Elderly, chronic constipation | Yes (torsion of vessels) | Infarction → perforation |
| Intussusception | Telescoping of proximal into distal bowel | Children 6 mo–3 yr (idiopathic); adults (mass) | Yes (mesenteric compression) | Necrosis, perforation |
- Adhesions are the #1 cause of small bowel obstruction (SBO) in adults with prior abdominal surgery. Hernias are the #1 cause in those without prior surgery.
- Volvulus most commonly affects the sigmoid colon, NOT the small intestine.
🧠 Testing Your Understanding!
Testing Your Understanding — LO 2, Question 1
A 6-month-old boy is brought to the ER with intermittent colicky abdominal pain, vomiting, and passage of red, jelly-like stools. Ultrasound shows a "target sign." His pediatrician notes he had a URI 2 weeks ago. What is the diagnosis, what is the most likely lead point, and how does this differ from the same diagnosis in a 55-year-old adult?
Consider: Peyer's patches, lymphoid tissue as lead point, malignancy risk in adults
In children, intussusception is often idiopathic or follows viral illness — reactive lymphoid hyperplasia (Peyer's patches) acts as the lead point. The ileocecal junction is the most common site. In adults, intussusception has a pathologic lead point in ~90% of cases (polyp, lipoma, lymphoma, adenocarcinoma), so workup must rule out malignancy. Management in children: air/barium enema (diagnostic + therapeutic). Adults often require surgery.
LO 3 — Vascular / Ischemic Bowel Disease
Bowel Infarction · Thrombosis vs. Embolism · Watershed Areas · HoyaDocs GI Block
- LO 3a: Discuss the risk factors for bowel infarction
- LO 3b: Distinguish between thrombotic and embolic etiologies; describe pathologic features
- LO 3c: Describe a patient with ischemic bowel disease; discuss potential complications
▼ Causes & Risk Factors
⭐ Ischemic bowel disease results from reduced blood flow to the intestinal wall — just like ischemic heart disease, it can be thrombotic or embolic in origin.
📌 Etiologies
| Mechanism | Details | Risk Factors |
|---|---|---|
| Arterial Embolism | Embolus from heart or proximal aorta lodges in mesenteric artery (usually SMA) | A-fib, valvular disease, recent MI, aortic atherosclerosis |
| Arterial Thrombosis | In-situ clot on atherosclerotic mesenteric artery | Atherosclerosis, hypercoagulable states |
| Venous Thrombosis | Mesenteric venous thrombosis → back-pressure ischemia | Hypercoagulable states (Factor V Leiden, malignancy, OCP use) |
| Non-occlusive (Shock) | Systemic hypotension → splanchnic vasoconstriction → mucosal ischemia | Cardiogenic shock, septic shock, major surgery |
🗺️ Watershed Areas — Most Vulnerable Sites
Watershed areas receive blood supply from the most distal branches of two arterial systems and are therefore most at risk when perfusion drops:
- Splenic Flexure — watershed between SMA and IMA (most vulnerable in hypotension)
- Rectosigmoid Junction — watershed between IMA and internal iliac
- Splenic flexure + rectosigmoid = classic watershed areas
- In a post-aortic surgery patient with bloody diarrhea → suspect ischemic colitis at the splenic flexure (IMA may have been sacrificed)
▼ Pathology & Clinical Presentation
⭐ The depth of injury depends on how long and how severe the ischemia is — from mucosal only (reversible) to transmural (life-threatening).
🔬 Histology
- Gross: Patchy distribution; hemorrhagic, congested, dusky-purple discoloration of bowel wall
- Mucosa: Hemorrhagic, ulcerated
- Key histologic finding: Coagulative necrosis of the bowel wall (ghost outlines of cells preserved)
- Pseudomembranes may form in severe colitis
- Mucosal ischemia: "Withering villi" — mucosal surface sloughs off first since it has the highest metabolic demand
🩺 Clinical Presentation
- Sudden onset crampy abdominal pain (often out of proportion to exam)
- Left lower quadrant pain (splenic flexure/sigmoid involvement)
- Bloody diarrhea (new onset of blood in stool)
- Nausea, vomiting
- Signs of shock if severe (tachycardia, hypotension)
⚠️ Complications
- Perforation → peritonitis → septic shock (major surgical emergency)
- Stricture — fibrosis during healing of ischemic segment
- Death — mesenteric ischemia has high mortality if full-thickness infarction occurs
- Classic Step 1 phrase for acute mesenteric ischemia: pain out of proportion to physical exam findings. The abdomen may be soft early on, even with severe ischemia.
- Elevated lactate is a key lab clue (anaerobic metabolism from ischemic gut).
🧠 Testing Your Understanding!
Testing Your Understanding — LO 3, Question 1
A 72-year-old man with a history of atrial fibrillation (on warfarin, but INR subtherapeutic) develops sudden, severe periumbilical pain, vomiting, and bloody diarrhea. His abdomen is soft with mild tenderness. Lactate is 6.2 mmol/L. What is the most likely diagnosis and mechanism? Which bowel segment is most at risk, and why?
Consider: embolic source, SMA territory, watershed zones, lactate significance
A-fib causes stasis and thrombus formation in the left atrium → embolism → SMA occlusion (the SMA comes off at a favorable angle for emboli). The small bowel and right colon (SMA territory) are most at risk acutely. The elevated lactate reflects anaerobic metabolism from ischemic bowel — a key prognostic marker. Pain out of proportion to exam is the classic early presentation. If untreated → bowel necrosis → perforation → septic shock with high mortality.
LO 4 — Malabsorption & Celiac Disease
4 Phases of Absorption · Diarrhea Types · Celiac Pathogenesis · HoyaDocs GI Block
- LO 4a: Discuss the pathogenesis of celiac disease and correlate with specific HLA types
- LO 4b: Describe a possible clinical scenario for a patient presenting with celiac disease
- LO 4c: Characterize the pathologic findings of celiac disease
- LO 4d: List extra-intestinal clinical manifestations
▼ Malabsorption Overview
⭐ Malabsorption = defective absorption of nutrients. At least one of four physiologic phases must be impaired.
📌 The 4 Phases of Absorption
| # | Phase | Location | Process | If Impaired |
|---|---|---|---|---|
| 1 | Intraluminal Digestion | Lumen | Proteins, carbs, fats broken down from large forms by enzymes (pancreatic lipase, proteases) | Steatorrhea, azotorrhea; seen in pancreatic insufficiency |
| 2 | Terminal Digestion | Brush border (SI) | Disaccharides and peptides broken down further by brush border enzymes (disaccharidases, peptidases) | Lactase deficiency → osmotic diarrhea |
| 3 | Transepithelial Transport | Enterocytes | Nutrients transported across and processed in small intestinal cells | Celiac disease → villous atrophy → reduced surface area |
| 4 | Lymphatic Transport | Lacteals | Chylomicrons transported into lymphatics | Lymphatic obstruction (Whipple's disease, lymphangiectasia) |
💧 Types of Diarrhea — Critical Step 1 Distinction
| Type | Mechanism | Key Feature | Example |
|---|---|---|---|
| Secretory | Active secretion of water/electrolytes into lumen | Does NOT stop with fasting; isotonic stool | Cholera, VIPoma |
| Osmotic | Unabsorbed solutes draw water into lumen osmotically | Stops with fasting; caused by nutrients in lumen | Lactase deficiency, laxative use |
| Malabsorptive | Nutrient passes completely through unabsorbed | Steatorrhea (greasy, foul-smelling, floating stools) | Celiac disease, pancreatic insufficiency |
| Exudative | Inflammation causes purulent/bloody stools | Does NOT stop with fasting; may be bloody | IBD, infectious colitis |
▼ Celiac Disease (Gluten-Sensitive Enteropathy)
⭐ Celiac disease is an immune-mediated disorder triggered by gluten ingestion in genetically susceptible individuals (HLA-DQ2 and HLA-DQ8).
🔬 Pathogenesis
- Gluten is digested into Gliadin (the immunogenic component)
- Gliadin stimulates the intestinal epithelium to produce IL-15
- IL-15 drives proliferation of CD8+ intraepithelial lymphocytes → direct epithelial damage
- Gliadin also crosses into the lamina propria and is deamidated by tissue transglutaminase (tTG)
- Deamidated gliadin binds to HLA-DQ2 or HLA-DQ8 on APCs → T cell activation → cytokine production → villous injury
- B cells produce anti-tTG IgA antibodies (and anti-endomysial Ab) — used for serologic diagnosis
- When gliadin activates the APC/T cell cascade, auto-antibodies against tissue transglutaminase in the epithelial cells are a downstream result. Anti-tTG is the best initial serologic test.
🧪 Diagnosis & Pathologic Findings
Serologic testing (non-invasive, done first):
- IgA anti-tissue transglutaminase (anti-tTG) — best initial test
- IgA anti-endomysial antibodies (highly specific)
- If IgA deficient → use IgG anti-tTG or IgG anti-DGP
- Absence of HLA-DQ8 and HLA-DQ2 essentially rules out celiac disease
Tissue biopsy (definitive — performed if serology positive):
| Histologic Finding | Significance |
|---|---|
| Villous atrophy | ↓ absorptive surface area → malabsorption |
| Crypt hyperplasia | Compensatory elongation of crypts |
| ↑ Intraepithelial CD8+ lymphocytes | >25 per 100 enterocytes is abnormal; driven by IL-15 |
| ↑ Plasma cells in lamina propria | Seen in fully developed disease |
🩺 Clinical Features & Extra-intestinal Manifestations
GI symptoms: Chronic diarrhea, bloating, abdominal distension, weight loss, fatigue, steatorrhea
Extra-intestinal manifestations (especially in children):
- Dermatitis herpetiformis — intensely pruritic papulovesicular rash on extensor surfaces; IgA deposits at the dermal-epidermal junction; pathognomonic for celiac
- Arthritis — joint pain, especially in children
- Iron-deficiency anemia — duodenum/proximal jejunum (iron absorption site) is damaged
- Osteoporosis — calcium malabsorption
- Neurologic symptoms — ataxia, peripheral neuropathy ("gluten ataxia")
- Infertility in women
- Short stature in children
Treatment: Strict gluten-free diet (avoidance of wheat, barley, rye) — may reduce long-term cancer risk
Long-term risk: Increased risk of malignancy — particularly T-cell lymphoma (enteropathy-associated T-cell lymphoma, EATL) and small bowel adenocarcinoma
- Both cause villous atrophy and malabsorption, but celiac is immune-mediated (gluten trigger, HLA-DQ2/DQ8, anti-tTG positive) while tropical sprue is infectious (occurs in tropical regions, responds to antibiotics + folate).
- Celiac does NOT improve with antibiotics; it requires lifelong gluten avoidance.
🧠 Testing Your Understanding!
Testing Your Understanding — LO 4, Question 1
A 28-year-old woman presents with 6 months of watery diarrhea, bloating, and fatigue. She reports her diarrhea continues even when she fasts. Her CBC shows iron-deficiency anemia. She also complains of a pruritic rash on her elbows. IgA anti-tTG is markedly elevated. Small bowel biopsy shows villous atrophy with crypt hyperplasia. What type of diarrhea does she have? What is the diagnosis? Explain the pathogenesis connecting gluten to villous atrophy.
Consider: diarrhea classification, malabsorptive vs. secretory features, gliadin → IL-15 → CD8+ lymphocytes → villous injury, dermatitis herpetiformis
The diarrhea is malabsorptive — nutrient passes through unabsorbed, causing steatorrhea. (Note: it does not stop with fasting since inflammation and impaired transport persists.) Pathogenesis: dietary gluten → gliadin fragment → stimulates IL-15 production → CD8+ intraepithelial lymphocyte proliferation → direct epithelial damage. Gliadin also crosses into lamina propria, deamidated by tTG → presented on HLA-DQ2/DQ8 → T cell activation → cytokine storm → villous atrophy. The pruritic rash is dermatitis herpetiformis (IgA deposits at the DEJ), pathognomonic for celiac. Treatment: strict gluten-free diet.
LO 5 — Inflammatory Bowel Disease (IBD)
Crohn Disease · Ulcerative Colitis · Comparison · HoyaDocs GI Block
- LO 5a: Define Crohn disease; list characteristic histologic features, symptoms, and potential complications
- LO 5b: Define ulcerative colitis; list defining pathologic and clinical features
- LO 5c: Compare and contrast Crohn disease vs. ulcerative colitis
- LO 5d: Describe potential complications of UC including risk of carcinoma; discuss dysplasia and colitis-associated neoplasia
▼ IBD Overview
⭐ IBD is a chronic condition arising from complex interactions between intestinal microbiota and host immunity. Exact etiology unknown. Two diseases fall under this category: Crohn Disease and Ulcerative Colitis.
- Both are immune-mediated with relapsing-remitting course
- Both associated with extraintestinal manifestations: arthritis, uveitis, skin lesions (pyoderma gangrenosum, erythema nodosum), liver disease (primary sclerosing cholangitis — more common in UC)
- Triggers: Stress, cigarettes (Crohn), diet, infections
- Key difference in cancer risk: UC has significantly higher colorectal cancer risk vs. Crohn
▼ Crohn Disease
⭐ Crohn disease can involve any part of the GI tract from mouth to anus, causes transmural inflammation, and characteristically shows skip lesions.
📍 Distribution
- Any part of GI tract — mouth to anus; most commonly terminal ileum, ileocecal valve, and cecum
- Skip lesions — segments of diseased bowel separated by areas of normal mucosa ("cobblestone" appearance from linear ulcers and submucosal edema)
- Does NOT begin in the rectum (contrast with UC)
🔬 Pathology
- Transmural inflammation — involves all layers of bowel wall (mucosa through serosa)
- Fibrosis — transmural fibrosis can lead to strictures
- Non-caseating granulomas — pathognomonic when present (only ~60% of cases); distinguish from TB (which is caseating)
- Ulcerations, fissures, fistulas — deep linear fissures can form fistulas to adjacent organs (enteroenteric, enterovesical, enterocutaneous, perianal)
- Acute histology: Neutrophilic infiltrate, crypt destruction, may see crypt abscesses
- Chronic histology: Lymphocytic infiltrate, granulomas, crypt branching and distortion
🩺 Clinical Features & Complications
- Symptoms: Intermittent diarrhea (non-bloody or mildly bloody), abdominal pain and cramping, fever, weight loss; triggered by stress, cigarettes, certain foods
- Right lower quadrant pain — terminal ileum involvement mimics appendicitis
- Complications:
- Strictures → small bowel obstruction (fibrosis)
- Fistulas (perianal fistulas highly characteristic)
- Abscesses
- Malabsorption (terminal ileum damage → B12 and bile acid malabsorption)
- Colorectal cancer (lower risk than UC)
- Kidney stones (oxalate stones — fat malabsorption → fatty acids bind calcium → free oxalate absorbed)
▼ Ulcerative Colitis (UC)
⭐ UC is a continuous mucosal inflammation beginning in the rectum and extending proximally; it is limited to the colon and rectum and never involves the small intestine (except "backwash ileitis").
📍 Distribution
- Always begins in the rectum and extends proximally (retrograde) in a continuous fashion
- Limited to colon and rectum — never involves small bowel (except backwash ileitis at the terminal ileum in pancolitis)
- Pancolitis = entire colon involved (highest cancer risk)
🔬 Pathology
- Mucosal and submucosal inflammation only — NOT transmural (key contrast with Crohn)
- Crypt abscesses — neutrophils fill and distend crypts; pathognomonic (though also seen in Crohn)
- Crypt distortion — branching, irregular gland architecture from chronic injury
- Pseudopolyps — islands of regenerating mucosa surrounded by ulcerated areas; seen grossly
- Red ulcers in the affected intestine
- No granulomas (contrast with Crohn)
🩺 Clinical Features
- Attacks of bloody diarrhea with stringy mucoid material — classic presentation; symptoms may persist days to months
- First episode often associated with psychological stress
- Tenesmus (sensation of incomplete evacuation), urgency
🎗️ Complications & Cancer Risk
- Primary Sclerosing Cholangitis (PSC) — fibro-obliterative disease of bile ducts; strongly associated with UC (not Crohn); patients may present with elevated ALP and bilirubin
- Toxic megacolon — severe transmural inflammation (acute complication) → colonic dilation >6cm → perforation risk
- Colorectal carcinoma — significantly elevated risk, proportional to:
- Duration of disease
- Extent of colitis (pancolitis highest risk)
- Degree of histologic dysplasia
- Colitis-associated dysplasia: Low-grade dysplasia → high-grade dysplasia → adenocarcinoma; surveillance colonoscopy mandatory every 1-2 years after 8-10 years of disease
- Histologic dysplasia features: Loss of mucin, nuclear crowding, nuclear enlargement and hyperchromasia, architectural disarray
- PSC is strongly associated with UC, not Crohn. When you see elevated ALP + biliary strictures + IBD, think UC + PSC.
- PSC itself significantly increases the risk of cholangiocarcinoma.
▼ Crohn Disease vs. Ulcerative Colitis — Master Comparison
| Feature | Crohn Disease | Ulcerative Colitis |
|---|---|---|
| Location | Any part of GI tract (mouth to anus); most common: terminal ileum, ileocecal valve | Colon and rectum ONLY |
| Pattern | Skip lesions (discontinuous) | Continuous, starts in rectum |
| Rectum involvement | Often spared | Always involved (100%) |
| Depth of inflammation | Transmural (all layers) | Mucosa and submucosa only |
| Granulomas | Yes (non-caseating; ~60%) | No |
| Crypt abscesses | Occasional | Classic, common |
| Gross appearance | Cobblestone mucosa, fissures, fistulas | Pseudopolyps, red ulcers, friable mucosa |
| Fistulas/Strictures | Yes (transmural fibrosis) | Rare |
| Bloody diarrhea | Intermittent, less prominent | Classic; bloody + mucoid |
| Cancer risk | Slightly increased | Significantly increased (pancolitis) |
| PSC association | Rare | Yes (strong) |
| Smoking effect | Worsens disease | Protective (paradoxically) |
| Surgery curative? | No (disease recurs) | Yes (colectomy is curative) |
🧠 Testing Your Understanding!
Testing Your Understanding — LO 5, Question 1
A 24-year-old woman presents with 3 months of intermittent bloody diarrhea with mucus, urgency, and crampy lower abdominal pain. Colonoscopy shows continuous mucosal erythema and pseudopolyps starting at the rectum and extending to the splenic flexure. Biopsy shows crypt abscesses and crypt architectural distortion. Liver function tests show an elevated ALP. What is the diagnosis? What associated hepatobiliary condition should you suspect, and why does this patient have an increased cancer risk?
Consider: rectum always involved, continuous pattern, PSC, duration of disease → dysplasia → CRC
The continuous mucosal inflammation starting in the rectum, pseudopolyps, crypt abscesses, and bloody mucoid diarrhea are classic for UC. PSC (fibro-obliterative inflammation of bile ducts → elevated ALP, bilirubinemia) has a strong association with UC specifically. Cancer risk in UC is proportional to disease extent and duration — this patient with left-sided colitis has intermediate risk; pancolitis carries the highest risk. After 8-10 years of disease, surveillance colonoscopy every 1-2 years is mandatory to detect colitis-associated dysplasia.
LO 6 — Diverticular Disease (Colon)
Pseudo-Diverticula · Sigmoid Colon · Diverticulitis · HoyaDocs GI Block
- LO 6a: Describe a patient with diverticular disease
- LO 6b: Characterize the pathogenesis and etiology of diverticular disease
- LO 6c: Define diverticulitis and list potential complications
▼ Clinical Features
⭐ Diverticular disease refers to acquired pseudo-diverticula of the colon — outpouchings of mucosa and submucosa (NOT all 3 layers) alongside the tenia coli of the sigmoid colon.
📌 Description
- Size: 0.5–1 cm flask-like outpouchings of colonic mucosa and submucosa
- Location: Alongside the tenia coli (longitudinal muscle bands of the colon)
- Distribution: Predominantly the sigmoid colon (highest intraluminal pressure); ascending colon involvement more common in Asians
- NOT a true diverticulum — involves only mucosa and submucosa, not the muscularis propria (pseudo-diverticula)
- Usually asymptomatic — may cause cramping, discomfort, constipation, or a feeling of incomplete emptying
- Demographics: Increasingly common with age; prevalence >60% in patients over 60 years old in Western countries
- Diverticulosis: Presence of diverticula without inflammation — usually asymptomatic
- Diverticular disease: Symptomatic diverticulosis (cramping, discomfort)
- Diverticulitis: Inflammation/infection of a diverticulum — LEFT lower quadrant pain, fever, leukocytosis ("left-sided appendicitis")
▼ Pathogenesis & Etiology
⭐ The key driver is increased intraluminal pressure causing herniation of mucosa through anatomical weak points in the bowel wall.
🔬 Mechanism
- Low-fiber diet → reduced stool bulk → increased colonic segmental contractions to move small, hard stool
- Increased intraluminal pressure exaggerated by peristaltic contractions
- Anatomical weak points are created where nerves and arterial vasa recta penetrate through the inner circular muscle layer — these gaps allow mucosal herniation
- Pressure → mucosal herniation through lamina propria → pseudo-diverticulum forms alongside tenia coli
- Sigmoid has the smallest lumen diameter → highest intraluminal pressure (LaPlace's law: pressure = force/area)
- It also has the greatest number of segmental contractions
Often resolves spontaneously if small; surgery if severe (multiple or large diverticula)
▼ Diverticulitis & Complications
⭐ Diverticulitis occurs when a diverticulum perforates (micro- or macro-perforation) → local inflammation and potential spread of infection.
🩺 Diverticulitis Presentation
- Left lower quadrant pain, tenderness ("left-sided appendicitis")
- Fever, leukocytosis
- Change in bowel habits (constipation or diarrhea)
- CT abdomen: thickening of the sigmoid wall, pericolonic fat stranding, pericolic abscess
⚠️ Complications
| Complication | Mechanism | Clinical Feature |
|---|---|---|
| Perforation | Micro/macro-perforation of diverticulum | Peritonitis, sepsis (emergency) |
| Pericolonic abscess | Contained perforation with pus collection | Mass effect, fever, pain; CT-guided drainage |
| Sinus tract / Fistula | Extension of inflammation to adjacent organs | Colovesical fistula → pneumaturia, fecaluria; colovaginal fistula |
| Fibrosis / Stricture | Healing of repeated inflammation | Bowel obstruction; may mimic carcinoma on imaging |
🧠 Testing Your Understanding!
Testing Your Understanding — LO 6, Question 1
A 68-year-old man presents with 2 days of left lower quadrant pain, low-grade fever, and constipation. CT scan shows sigmoid wall thickening with pericolonic fat stranding and a small pericolic fluid collection. He is started on antibiotics. On day 3, his pain worsens and he develops pneumaturia (air in urine). What complication has occurred? What anatomic structure has become involved, and how does this relate to the original pathology?
Consider: diverticulitis → perforation → fistula formation → adjacent organ involvement
The diverticulitis has progressed to form a colovesical fistula — a tract between the inflamed sigmoid colon and the urinary bladder (which lies anteriorly). Fecal matter and bacteria enter the bladder, causing pneumaturia (air passed in urine), fecaluria, and recurrent UTIs with colonic flora. This is the most common type of fistula complicating diverticulitis. The underlying pathology: pseudo-diverticulum → microperforation → pericolonic inflammation → fistula formation to adjacent bladder.
LO 7 — Colonic Polyps
Nonneoplastic · Hamartomatous Syndromes · Adenomas · HoyaDocs GI Block
- LO 7: Define polyp and describe gross subtypes including risk factors, clinical and pathologic features, and associated syndromes
▼ Polyp Overview & Classification
⭐ A polyp is a nonspecific term for any growth that protrudes into the lumen of the GI tract. They can occur anywhere and range from completely benign to premalignant.
📌 Morphologic Classification
- Sessile — flat, no stalk; grows directly from mucosal surface (harder to remove endoscopically)
- Pedunculated — has a stalk (easier to snare and remove)
| Category | Types | Malignant Potential |
|---|---|---|
| Nonneoplastic | Inflammatory (reactive), Hyperplastic, Hamartomatous (Juvenile, Peutz-Jegher) | Generally NO (but syndromes carry risk) |
| Neoplastic | Tubular adenoma, Tubulovillous adenoma, Villous adenoma, Sessile Serrated Adenoma | YES — all adenomas have malignant potential |
▼ Nonneoplastic Polyps
⭐ Nonneoplastic polyps do not have intrinsic malignant potential, but they are clinically important to recognize and distinguish from neoplastic lesions.
🔬 Inflammatory Polyps
- Origin: Chronic cycles of mucosal injury and repair
- Risk factors: IBD (especially UC), other chronic injury
- Histology: Mixed inflammatory infiltrates, erosion, epithelial hyperplasia with prolapse-induced LP fibromuscular hyperplasia
- Associated syndrome: Solitary Rectal Ulcer Syndrome — straining during defecation, sense of incomplete evacuation, passage of blood and mucus per rectum; caused by localized ischemic injury or prolapse of distal rectal mucosa
🔬 Hyperplastic Polyps
- Definition: Benign epithelial proliferation due to decreased epithelial turnover and delayed shedding of surface epithelial cells
- Demographics: Adults in 6th–7th decades
- Location: Small, often in left colon (sigmoid and rectum)
- Gross: Small, pale nodules; reactive, non-neoplastic
- Histology: "Piling up" of goblet and absorptive cells; star-shaped/serrated lumen when cut in cross-section
- Malignant potential: NONE by itself — but must be distinguished from sessile serrated adenoma (similar histology but malignant potential!)
- Both show serrated/star-shaped lumen on histology. Key difference: sessile serrated adenoma (SSA) has serrated architecture extending to the crypt base with crypt dilation and lateral growth — hyperplastic polyps do NOT have crypt base involvement.
- SSAs are found in the right colon and have malignant potential via the MSI pathway.
▼ Hamartomatous Polyp Syndromes
⭐ Hamartomatous polyps consist of disorganized but normally occurring tissue elements. Solitary hamartomas are usually benign, but syndromes carry significant malignant risk.
🧒 Juvenile Polyps & Juvenile Polyposis Syndrome
- Definition: Focal malformations of epithelium and lamina propria
- Demographics: Young children; most common site is the rectum; may bleed
- Gross: Pedunculated with cystic spaces
- Complications: Intussusception, obstruction, or prolapse (may be associated)
Juvenile Polyposis Syndrome:
- SMAD4 mutation — most common (encodes intermediate in TGF-beta signaling)
- BMPR1A mutation — second most common (also TGF-beta superfamily)
- 30–50% of patients develop colonic adenocarcinoma
- Associated with congenital malformations and digital clubbing
🔑 Peutz-Jegher Syndrome (PJS)
- Genetics: Autosomal dominant; LOF mutation in STK11 gene (LKB1 — tumor suppressor) in ~½ of individuals
- Polyps: Most common in small intestine (also colon and stomach); large and pedunculated with lobulated contour
- Histology: Mix of connective tissue, smooth muscle, lamina propria, and glands lined by normal-appearing intestinal epithelium; presence of smooth muscle is the distinguishing histologic feature
- Classic triad for diagnosis:
- Multiple polyps in the small intestine
- Mucocutaneous hyperpigmentation (dark spots around the mouth, lips, buccal mucosa, fingers)
- Positive family history
- Malignancy risk: Significantly increased risk of GI (pancreas, colon, small bowel) and extra-GI (breast, lung, ovary, uterus) malignancies
- PJS: mucocutaneous dark spots (perioral) + GI hamartomas + STK11 mutation
- The smooth muscle arborizing core is the pathognomonic histologic feature of PJS polyps
▼ Neoplastic Polyps (Adenomas)
⭐ Adenomas are intraepithelial neoplasms characterized by epithelial dysplasia. All adenomas have malignant potential; size is the most important factor correlating with malignancy risk.
📊 Adenoma Subtypes
| Type | Features | Location | Malignancy Risk |
|---|---|---|---|
| Tubular Adenoma | Tubular glands with dysplasia; most common type; pedunculated or sessile | Any colon; left sided predominance | Lowest of adenomas (~5%) |
| Tubulovillous Adenoma | Mixed tubular and villous architecture; intermediate features | Any colon | Intermediate |
| Villous Adenoma | Finger-like projections; large, sessile; may secrete mucus → watery diarrhea with hypokalemia | Rectosigmoid | Highest (~40%) |
| Sessile Serrated Adenoma (SSA) | Serrated architecture throughout glands including crypt base; crypt dilation; lateral growth; resembles hyperplastic polyp | Right colon predominance | Significant (MSI pathway) |
📌 Key Facts: Tubular Adenoma
- Present in ~30% of adults age 60 or older
- Size is the most important predictor of malignancy — the larger, the higher the risk
- Surveillance colonoscopy begins at age 45–50 in average-risk individuals
- Most adenomas are asymptomatic; size 0.3–10 cm
📌 Key Facts: Sessile Serrated Adenoma
- Most common in right colon
- Lacks the typical cytologic dysplasia seen in tubular adenomas (making it harder to recognize)
- Serrated architecture throughout entire gland length, including the crypt base — this distinguishes it from hyperplastic polyps (which are serrated only at the surface)
- Additional features: crypt dilation and lateral growth pattern
- Progresses via the microsatellite instability (MSI) pathway (see LO 8)
🧠 Testing Your Understanding!
Testing Your Understanding — LO 7, Question 1
A 17-year-old boy presents with recurrent episodes of colicky abdominal pain. Physical exam shows dark pigmented macules on his lips and buccal mucosa. His mother had similar pigmentation and died of pancreatic cancer at age 42. Colonoscopy shows multiple large pedunculated polyps in the small bowel. Biopsy reveals glands lined by normal-appearing epithelium within a core of smooth muscle and connective tissue. What is the diagnosis? What gene is mutated? What malignancies is he at increased risk for?
Consider: smooth muscle in polyp core, perioral pigmentation, family history, STK11, extraintestinal cancer risk
Classic PJS triad: (1) multiple GI hamartomatous polyps in the small intestine, (2) mucocutaneous hyperpigmentation around the mouth/lips, and (3) positive family history (AD inheritance). The pathognomonic histologic feature is smooth muscle arborizing through the polyp core, with overlying normal epithelium. He is at significantly increased risk for GI malignancies (pancreas, small bowel, colon, stomach) and extra-GI malignancies (breast, lung, ovary, uterus, cervix). His mother's pancreatic cancer at 42 is consistent with STK11-associated cancer risk.
LO 8 — Colorectal Carcinoma & Familial Syndromes
Adenoma-Carcinoma Sequence · FAP · Lynch Syndrome · Anal Canal · HoyaDocs GI Block
- LO 8a: Discuss the adenoma-carcinoma sequence for neoplastic polyps and list pertinent molecular factors
- LO 8b: Characterize familial adenomatous polyposis (FAP) and discuss risk of carcinoma
- LO 8c: Characterize hereditary non-polyposis colorectal cancer (HNPCC/Lynch syndrome)
- LO 8d: Describe tumors of the anal canal and hemorrhoids
▼ Adenoma-Carcinoma Sequence
⭐ Colorectal cancer develops through two major molecular pathways. Most CRCs develop from adenomas over 10–15 years.
Dietary risk factors: Low intake of non-absorbable fiber, high refined carbohydrates, high fat intake → reduced stool bulk → increased mucosal contact with toxic bacterial metabolites → mutagenesis
🧬 Pathway 1: APC/B-Catenin (Chromosomal Instability)
This is the classic Vogelstein adenoma-carcinoma sequence — involves two-hit tumor suppressor inactivation and is slower (~10–15 years):
| Step | Gene / Event | Significance |
|---|---|---|
| 1st hit | APC at 5q21 (germline or somatic mutation) | APC normally degrades beta-catenin; loss → Wnt signaling activated → cell proliferation |
| 2nd hit | Methylation abnormalities → K-RAS activation (12p12) | Proto-oncogene activation → proliferative advantage |
| 3rd hit | Homozygous loss of TP53 (17p13), LOH at 18q21 (SMAD2/4) | Loss of apoptosis checkpoint; TGF-beta signaling loss |
| Result | Additional chromosomal alterations → carcinoma | COX-2 overexpression also noted |
"A K(e)y S(afe) T(ransaction)"
- A — APC (5q21) — first mutation
- K — K-RAS (12p12) — proliferation
- S — SMAD2/4 loss (18q21) — loss of TGF-beta brakes
- T — TP53 loss (17p13) — loss of apoptosis
🧬 Pathway 2: Microsatellite Instability (MMR Deficiency)
This pathway involves defects in DNA mismatch repair (MMR) genes. It progresses faster and through sessile serrated adenomas:
- Germline mutations: MLH1, MSH2 (Lynch syndrome) → hereditary
- Sporadic: Hypermethylation of MLH1 promoter → MLH1 silencing → MMR deficiency
- MMR deficiency → microsatellite instability (accumulation of errors in repeat sequences throughout genome)
- Normal colon → Sessile serrated adenoma → carcinoma (via BRAF mutation, TGFBRII, BAX, IGF2R, others)
- Associated with: Right-sided colon cancer, mucinous histology, better prognosis (despite worse stage at diagnosis in HNPCC)
🔬 Gross & Microscopic Features of Colorectal Adenocarcinoma
| Location | Gross Appearance | Clinical Consequence |
|---|---|---|
| Proximal colon (right-sided) | Polypoid, exophytic masses growing into lumen | Rarely cause obstruction; present with occult blood, iron-deficiency anemia |
| Distal colon (left-sided) | Annular "napkin-ring" lesions that constrict the lumen | Change in bowel habits, obstruction, pencil-thin stools, hematochezia |
Microscopic: Gland-forming adenocarcinoma; invades bowel wall; may have mucin production
Two most important prognostic factors:
- Depth of invasion (T stage) — invasion into muscularis propria = worse prognosis
- Lymph node metastasis (N stage) — single most powerful predictor
Spread: Direct invasion → lymphatics → hematogenous (portal vein → liver is most common site of metastasis; lung second)
▼ Familial Adenomatous Polyposis (FAP)
⭐ FAP is the most dramatic of the adenomatous polyposis syndromes — left untreated, cancer is virtually inevitable.
📌 Key Features
- Genetics: Autosomal dominant mutation in the APC gene (5q21)
- Polyp burden: ≥100 adenomatous polyps required for diagnosis; most patients have thousands
- Polyp type: Flat (non-polypoid) tubular adenomas predominate
- Cancer risk: 100% risk of colorectal carcinoma in untreated patients, typically by age 30
- Treatment: Prophylactic colectomy (usually in late teens/early 20s)
- Gardner syndrome: FAP variant with additional extracolonic features — osteomas, desmoid tumors, congenital hypertrophy of retinal pigment epithelium (CHRPE), sebaceous cysts
- Turcot syndrome: FAP + CNS tumors (medulloblastoma with APC; glioblastoma with MMR defects)
- APC mutation → FAP → 100% CRC → prophylactic colectomy
- Gardner = FAP + osteomas + desmoids
- Turcot = FAP + brain tumor (medulloblastoma)
▼ Lynch Syndrome (HNPCC)
⭐ Lynch syndrome is the most common hereditary colorectal cancer syndrome, caused by germline mutations in DNA mismatch repair genes — NO polyposis is required.
📌 Key Features
| Feature | Lynch Syndrome (HNPCC) | FAP |
|---|---|---|
| Gene | MSH2 or MLH1 (DNA mismatch repair) | APC (tumor suppressor) |
| Mechanism | Microsatellite instability | APC/B-catenin chromosomal instability |
| Polyp burden | Few polyps (not florid polyposis) | 100s–1000s of polyps |
| Location | Right colon (proximal) | Left colon predominance (flat adenomas) |
| Age of onset | Younger (40–50 yrs) | Younger (CRC by age 30 if untreated) |
| Extra-colonic cancers | Endometrial (#1 in women), ovarian, gastric, small bowel, urothelial | Osteomas, desmoids (Gardner) |
| Prevalence | 2–4% of all CRC | <1% of CRC |
- 3 family members with Lynch-associated cancer
- 2 successive generations affected
- 1 diagnosed before age 50
- And one is a first-degree relative of the other two
▼ Anal Canal Tumors & Hemorrhoids
🔬 Anal Canal Anatomy & Tumor Types
The anal canal can be divided into thirds by epithelial lining:
| Zone | Epithelium | Tumor Type |
|---|---|---|
| Upper third | Columnar rectal epithelium | Adenocarcinoma (same as colorectal) |
| Middle third (transitional zone) | Transitional (cloacogenic) epithelium | Transitional cell carcinoma |
| Lower third | Stratified squamous epithelium | Squamous cell carcinoma (most important) |
Squamous cell carcinoma of the anal canal:
- Frequently associated with HPV infection (high-risk strains, particularly HPV 16 and 18)
- Risk factors: multiple sexual partners, anal receptive intercourse, immunosuppression
- Nigerent's regimen (Nigro protocol) with chemoradiation (5-FU + mitomycin + radiation) often curative
🩸 Hemorrhoids
- Definition: Dilated, tortuous veins of the hemorrhoidal plexus — anal varices
- Cause: Persistent increased pressure on hemorrhoidal plexus
- Risk factors: Straining during defecation (most common), pregnancy, chronic constipation, cirrhosis/portal hypertension
- Internal hemorrhoids (above dentate line): painless; drain via superior rectal vein → portal system
- External hemorrhoids (below dentate line): painful; drain via inferior rectal vein → systemic
- Presentation: Bright red blood per rectum (BRBPR), pain; bleeding not usually a medical emergency but can be chronic and cause iron-deficiency anemia
- Rectal bleeding attributed to hemorrhoids in a patient over 50 should still prompt colonoscopy to rule out colorectal cancer. Hemorrhoids are common, but so is CRC — don't let one diagnosis mask the other.
🧠 Testing Your Understanding!
Testing Your Understanding — LO 8, Question 1
A 38-year-old woman presents for colonoscopy after her mother and maternal uncle both developed colon cancer in their early 40s. Her colonoscopy shows only 3 adenomatous polyps in the right colon. Genetic testing reveals a germline MSH2 mutation. What syndrome does she have? What is the mechanism by which MMR gene loss leads to cancer? What other cancers must you screen her for?
Consider: MSI pathway, right-sided cancer, endometrial/ovarian cancer risk, no florid polyposis
MSH2 encodes a mismatch repair protein. Without functional MMR, errors in microsatellite repeat sequences (short tandem repeats prone to replication slippage) go uncorrected. This "mutator phenotype" accumulates mutations in growth-regulating genes (TGFBRII, BAX, etc.) → carcinogenesis. Lynch is characterized by few polyps (not thousands like FAP), right-sided colon cancer, and younger age of onset. Extra-colonic cancer screening is critical: endometrial cancer (highest risk in women), ovarian, gastric, small bowel, urothelial cancers. Annual gynecologic exam + transvaginal ultrasound + endometrial biopsy are recommended.
Practice Questions
Lectures 19–20 — Intestinal Pathology I & II · HoyaDocs GI Block
LO 1 — Congenital Anomalies & Diverticula (Q1–Q3)
Question 1
A 2-year-old boy presents with painless, bright red rectal bleeding. He has no prior history of GI problems. An abdominal scan using technetium-99m pertechnetate shows a focal area of uptake in the right lower abdomen. What is the most likely diagnosis, and what tissue accounts for the radionuclide uptake?
A. Appendicitis with mucosal ulceration
B. Meckel diverticulum with ectopic gastric mucosa
C. Intussusception with mesenteric ischemia
D. Crohn disease with terminal ileal involvement
E. Juvenile polyp with superficial erosion
Technetium-99m pertechnetate is taken up by gastric mucosa (both native and ectopic). Meckel diverticulum is the most common cause of painless lower GI bleeding in children under 2 (the Rule of 2's: 2% incidence, within 2 feet of ileocecal valve, 2 inches long, symptomatic by age 2). Ectopic gastric mucosa secretes acid → ulceration of adjacent ileal mucosa → bleeding. The Meckel scan (nuclear medicine) detects this ectopic gastric tissue.
Question 2
A newborn fails to pass meconium in the first 48 hours of life. Abdominal X-ray shows massive dilation of the proximal colon. Rectal examination produces an explosive release of gas and stool. Biopsy of the rectosigmoid reveals absence of ganglion cells in both the myenteric and submucosal plexuses. Which of the following best explains the underlying molecular defect?
A. Gain-of-function mutation in K-RAS
B. Loss-of-function mutation in APC
C. Loss-of-function mutation in the RET receptor tyrosine kinase
D. Trinucleotide repeat expansion in a neural crest transcription factor
E. Frameshift mutation in the SMAD4 gene
Hirschsprung disease is caused by failure of neural crest cells to migrate to the colon, most commonly due to LOF mutations in RET. RET normally signals neural crest cell migration and survival; without it, cells undergo premature apoptosis or arrest before reaching the rectosigmoid. The result is an aganglionic segment at the rectum (always) extending proximally. The dilated colon is the normally-innervated segment above the aganglionic zone. Association with Down syndrome is important to remember.
Question 3
A 45-year-old woman with no prior surgeries presents with a small bowel obstruction. CT scan shows a segment of small bowel herniated through the right inguinal canal. The surgeon notes the bowel appears ischemic. Which of the following best describes what has occurred?
A. Volvulus of the sigmoid colon
B. Adhesion-related kinking of the ileum
C. Strangulated inguinal hernia
D. Intussusception at the ileocecal junction
E. Meckel diverticulum acting as a lead point
A hernia becomes strangulated when the herniated bowel is tightly constricted at the hernia ring, compromising its blood supply → ischemia → infarction if not emergently repaired. In patients without prior abdominal surgery, hernias (inguinal being most common) are the #1 cause of bowel obstruction. The ischemic appearance confirms strangulation rather than simple incarceration. This requires urgent surgical intervention.
LO 2 — Intestinal Obstruction (Q4–Q6)
Question 4
A 74-year-old man presents with sudden onset of severe abdominal distension and obstipation. He has a history of chronic constipation. Plain abdominal X-ray shows a massively dilated loop of large bowel with a "coffee bean" shape in the left lower quadrant. What is the most likely diagnosis?
A. Cecal volvulus
B. Sigmoid volvulus
C. Colonic intussusception
D. Large bowel obstruction due to carcinoma
E. Toxic megacolon from ulcerative colitis
The "coffee bean" sign on plain X-ray is the classic radiographic finding of sigmoid volvulus. The sigmoid colon is the most common site of volvulus because it has a long mesentery and relatively fixed points of attachment, making it prone to twisting around its mesenteric axis. Elderly patients with chronic constipation and redundant sigmoid colons are at highest risk. Initial management: endoscopic decompression; surgery if gangrenous.
Question 5
A 55-year-old woman who underwent an open appendectomy 20 years ago presents with crampy abdominal pain, vomiting, and inability to pass flatus for 24 hours. CT abdomen shows a transition point in the mid-ileum with dilated bowel proximal to it and collapsed bowel distally. No mass is identified. What is the most likely etiology of her small bowel obstruction?
A. Carcinoid tumor of the ileum
B. Crohn disease stricture
C. Post-surgical adhesions
D. External compression by lymphadenopathy
E. Intussusception with malignant lead point
Adhesions are the #1 cause of small bowel obstruction in adults with prior abdominal surgery (and the most common cause of SBO overall). Fibrous bands form between bowel loops and the peritoneum after any peritoneal irritation (surgery, infection, endometriosis). These bands can kink or compress bowel segments years to decades after the original surgery. Management: NPO/NG decompression initially; surgery if no improvement or signs of strangulation.
Question 6
A 10-month-old girl is brought to the emergency department with intermittent episodes of drawing up her legs, inconsolable crying, and passage of red, jelly-like stools. Between episodes she appears lethargic. Ultrasound shows a "target sign" in the right upper quadrant. What is the most appropriate next step?
A. Emergency laparotomy
B. Colonoscopy to identify lead point
C. Air or barium enema (diagnostic and therapeutic)
D. IV antibiotics and observation for 24 hours
E. Biopsy of the ileocecal junction
This is classic pediatric intussusception: episodic colicky pain + "currant jelly" stools (blood + mucus from mesenteric compression) + target sign on ultrasound. In children, the lead point is usually lymphoid hyperplasia (from recent viral URI) at the ileocecal junction. Air or barium enema is both diagnostic and therapeutic — the hydrostatic/pneumatic pressure reduces the telescoped bowel in ~80% of uncomplicated cases. Surgery is reserved for failed enema, peritonitis, or perforation. Note: in adults, always suspect a pathologic lead point (tumor) and proceed to surgery.
LO 3 — Ischemic Bowel Disease (Q7–Q9)
Question 7
A 68-year-old man with known atrial fibrillation (not on anticoagulation) develops sudden, severe periumbilical pain with nausea and vomiting. His abdomen is diffusely tender but soft. Labs show WBC 18,000 and lactate 7.2 mmol/L. CT angiography shows occlusion of the proximal superior mesenteric artery. What is the most likely etiology?
A. Mesenteric venous thrombosis from portal hypertension
B. Non-occlusive mesenteric ischemia from cardiogenic shock
C. Arterial embolism from a cardiac source
D. In-situ thrombosis on an atherosclerotic mesenteric plaque
E. Splenic flexure ischemia from aortic surgery
Untreated atrial fibrillation causes left atrial stasis → thrombus formation → embolism. The superior mesenteric artery (SMA) takes off at an angle favorable for embolic lodging. This causes acute mesenteric ischemia affecting the entire SMA territory (mid-jejunum to transverse colon). Classic features: pain out of proportion to exam (early), elevated lactate (anaerobic metabolism), high WBC. Mortality is high without emergent revascularization ± bowel resection. A-fib is the #1 cause of embolic mesenteric ischemia.
Question 8
A 72-year-old woman undergoes elective repair of an abdominal aortic aneurysm. On postoperative day 2, she develops left lower quadrant pain and bloody diarrhea. Colonoscopy shows pale, ischemic mucosa with hemorrhagic patches at the splenic flexure. Which of the following best explains this complication?
A. The superior mesenteric artery was inadvertently ligated during surgery
B. The inferior mesenteric artery, a branch from the aortic repair, was sacrificed
C. Portal hypertension developed from liver manipulation during surgery
D. Mesenteric venous thrombosis from postoperative hypercoagulability
E. Intussusception at the transverse colon from adhesion formation
The splenic flexure is a watershed area between the SMA and IMA. During aortic aneurysm repair, the IMA is often sacrificed (ligated). When collateral flow is insufficient, the splenic flexure becomes ischemic — it relies on IMA branches that are now absent. This is ischemic colitis post-aortoplasty, and the splenic flexure is the classic vulnerable site. Classic exam: post-aortic surgery + bloody diarrhea + ischemia at the splenic flexure.
Question 9
On histologic examination of a resected segment of ischemic bowel, you observe patchy mucosal ulceration, hemorrhagic discoloration, and preservation of "ghost outlines" of cells that have lost their cytoplasm. What type of necrosis does this represent, and what is the clinical significance?
A. Liquefactive necrosis — indicates bacterial infection of bowel wall
B. Caseous necrosis — indicates mycobacterial infection of the mesentery
C. Coagulative necrosis — indicates ischemic infarction of the intestinal wall
D. Fat necrosis — indicates enzymatic digestion of mesenteric adipocytes
E. Fibrinoid necrosis — indicates immune complex deposition in the vessel wall
Coagulative necrosis is the hallmark of ischemia (except in the brain, where it is liquefactive). The proteins denature and "coagulate," preserving the ghost outlines of cells and tissues. In ischemic bowel, you see patchy hemorrhagic mucosa with coagulative necrosis and eventual ulceration. If full-thickness (transmural) infarction occurs, perforation and peritonitis become life-threatening complications. The patchy distribution helps distinguish ischemic colitis from infectious colitis.
LO 4 — Malabsorption & Celiac Disease (Q10–Q12)
Question 10
A 32-year-old woman reports 8 months of diarrhea, bloating, and 12-lb weight loss. Her diarrhea contains greasy, foul-smelling stools that float in the toilet. Labs show microcytic anemia and low serum albumin. She also describes a pruritic rash on her elbows. IgA anti-tissue transglutaminase is markedly elevated. Small bowel biopsy shows increased intraepithelial lymphocytes, crypt hyperplasia, and villous atrophy. What is the diagnosis?
A. Crohn disease of the small intestine
B. Whipple disease
C. Celiac disease (gluten-sensitive enteropathy)
D. Tropical sprue
E. Microscopic colitis
The triad of steatorrhea + iron-deficiency anemia + dermatitis herpetiformis (pruritic papulovesicular rash on extensor surfaces) is classic for celiac disease. Anti-tTG IgA is the best screening test. Biopsy showing villous atrophy + crypt hyperplasia + increased intraepithelial CD8+ lymphocytes is diagnostic. The rash (DH) represents IgA immune complex deposition at the dermal-epidermal junction and is pathognomonic for celiac. Treatment: strict lifelong gluten-free diet. Risk of EATL (T-cell lymphoma) if untreated.
Question 11
A 7-year-old child with celiac disease is not following a gluten-free diet. His mother asks which HLA type confers susceptibility to this disease and why. Which of the following best explains the HLA association in celiac disease?
A. HLA-B27 presents gliadin peptides to CD4+ T cells in the lamina propria
B. HLA-DQ2 or HLA-DQ8 on APCs present deamidated gliadin peptides to CD4+ T cells, initiating inflammation
C. HLA-DR4 activates cytotoxic CD8+ T cells against enterocytes directly
D. HLA-A2 on B cells induces anti-gliadin IgE production causing eosinophilic enteritis
E. HLA-DQ2 activates NK cells to destroy crypt stem cells through perforin release
In celiac disease: Gliadin → deamidated by tissue transglutaminase (tTG) in the lamina propria → binds with high affinity to HLA-DQ2 (in ~95% of patients) or HLA-DQ8 → presented to CD4+ T cells → Th1 cytokine response → epithelial damage. Additionally, IL-15 drives CD8+ intraepithelial lymphocyte proliferation, which directly damages enterocytes. The absence of HLA-DQ2 and HLA-DQ8 makes celiac disease very unlikely (high negative predictive value). ~30% of the general population carry DQ2 but only ~1% develop celiac — additional environmental and genetic factors are required.
Question 12
Which of the following types of diarrhea stops with fasting and why?
A. Secretory diarrhea — bacteria continuously secrete toxins regardless of food intake
B. Exudative diarrhea — mucosal inflammation persists regardless of food intake
C. Osmotic diarrhea — unabsorbed food solutes are the osmotic driver, which disappears with fasting
D. Malabsorptive diarrhea — fatty acids continue to irritate the colon even without food
E. Inflammatory diarrhea — cytokine-mediated secretion is independent of luminal contents
Osmotic diarrhea occurs when unabsorbed solutes (e.g., maldigested lactose in lactase deficiency, or ingested laxatives) remain in the lumen and draw water in by osmosis. When the patient fasts, no new solute is ingested → osmotic gradient disappears → diarrhea stops. Contrast: Secretory diarrhea (e.g., cholera, VIPoma) does NOT stop with fasting because the secretory stimulus (cAMP, toxin, VIP) is independent of luminal nutrients. This distinction is a classic Step 1 testing point.
LO 5 — Inflammatory Bowel Disease (Q13–Q16)
Question 13
A 26-year-old man presents with 6 months of crampy right lower quadrant pain, non-bloody diarrhea, fever, and 15-lb weight loss. He is a smoker. Colonoscopy shows skip lesions in the terminal ileum and cecum with deep linear ulcers and a "cobblestone" mucosa. Biopsy shows transmural inflammation with non-caseating granulomas. Which of the following complications is he most at risk for?
A. Primary sclerosing cholangitis
B. Colorectal carcinoma within 1 year
C. Fistula formation between the ileum and bladder
D. Toxic megacolon requiring immediate colectomy
E. Pseudomembranous colitis from C. difficile superinfection
Crohn disease causes transmural inflammation → linear fissuring ulcers that can penetrate through all bowel wall layers → fistulas to adjacent structures. Enteroenteric, enterovesical (causing pneumaturia and fecaluria), enterocutaneous, and perianal fistulas are characteristic of Crohn. PSC is associated with UC, not Crohn. Toxic megacolon is more typical of UC. Cancer risk in Crohn is elevated but less dramatic than in UC pancolitis. Fistulas + perianal disease + cobblestone mucosa + skip lesions = Crohn.
Question 14
A pathologist examining a colonic biopsy from a patient with known 15-year history of pancolitis due to UC describes neutrophils filling and expanding multiple crypts, creating "pus-filled" glands. These crypts are branched and architecturally distorted compared to the uniform tubular structure of normal crypts. What terms describe these two findings respectively?
A. Pseudopolyps and villous atrophy
B. Crypt abscesses and crypt architectural distortion
C. Transmural granulomas and skip lesions
D. Goblet cell depletion and paneth cell metaplasia
E. Lymphocytic infiltrate and fibromuscular hyperplasia
Crypt abscesses (neutrophils within and distending crypt lumens) are a hallmark of UC and acute IBD flares. Crypt architectural distortion (branching, irregular, non-parallel crypts) reflects chronic mucosal remodeling from repeated cycles of injury and repair — it is the pathologist's clue to chronicity of IBD. After 15 years of pancolitis, this patient also needs close surveillance for colitis-associated dysplasia and CRC. Regular colonoscopy with biopsies is mandatory every 1-2 years.
Question 15
A 35-year-old man with a 10-year history of UC (pancolitis) develops markedly elevated alkaline phosphatase and bilirubin. ERCP shows "beading" of the intrahepatic bile ducts with alternating strictures and dilations. What is the most likely diagnosis, and with which form of IBD is it characteristically associated?
A. Cholangiocarcinoma; Crohn disease
B. Primary biliary cholangitis; Crohn disease
C. Primary sclerosing cholangitis; ulcerative colitis
D. Secondary biliary cirrhosis; ulcerative colitis
E. Autoimmune hepatitis; indeterminate colitis
PSC is a fibro-inflammatory condition affecting the intra- and extrahepatic bile ducts, causing progressive stricturing → cholestasis → cirrhosis. The ERCP "beads on a string" pattern of alternating strictures and dilations is classic. PSC has a strong association with UC (70-80% of PSC patients have UC). Importantly, colectomy does NOT cure PSC — they are separate disease processes. PSC significantly increases the risk of cholangiocarcinoma. p-ANCA is positive in both UC and PSC.
Question 16
A patient with 20-year history of UC pancolitis undergoes surveillance colonoscopy. The pathologist reports "low-grade dysplasia" in a flat lesion in the sigmoid colon. Histologically, the glands show nuclear stratification, crowding, and loss of mucin production, but the basement membrane is intact. What is the significance of this finding and what should be done?
A. This is reactive inflammation only; continue annual surveillance
B. This represents low-grade colitis-associated dysplasia; increased surveillance or colectomy discussion warranted
C. This is pseudopolyp formation; no action needed beyond biopsy confirmation
D. This represents high-grade dysplasia; immediate colectomy is required
E. These histologic findings indicate transition to Crohn disease; switch therapy
Colitis-associated neoplasia progresses through a dysplasia-carcinoma sequence: mucosal inflammation → reactive changes → low-grade dysplasia → high-grade dysplasia → invasive adenocarcinoma. Low-grade dysplasia (LGD) shows nuclear enlargement, hyperchromasia, stratification, and mucin depletion, but the basement membrane remains intact (not invasive). LGD in the setting of UC is a significant finding — it confers a 10-fold increased risk of progressing to HGD or carcinoma. Current guidelines recommend enhanced surveillance (every 3-6 months) or discussion of prophylactic colectomy depending on the extent and confirmability of findings.
LO 6 — Diverticular Disease (Q17–Q18)
Question 17
A 65-year-old woman presents with left lower quadrant pain, low-grade fever, and constipation for 3 days. She has no prior history of colorectal cancer. CT shows thickening of the sigmoid colon wall with pericolonic fat stranding. No free air is identified. Which of the following best describes the pathologic lesion causing her symptoms?
A. True diverticulum (all 3 layers) of the sigmoid colon with acute inflammation
B. Pseudo-diverticulum (mucosa + submucosa only) of the sigmoid colon with inflammation (diverticulitis)
C. Transmural inflammation of the sigmoid colon consistent with Crohn disease
D. Adenocarcinoma of the sigmoid colon with local invasion
E. Ischemic colitis at the splenic flexure from IMA thrombosis
Colonic diverticula are pseudo-diverticula (only mucosa and submucosa herniate through the muscular wall — NOT all 3 layers). They form predominantly in the sigmoid colon due to highest intraluminal pressure. Diverticulitis ("left-sided appendicitis") occurs when a diverticulum perforates (micro- or macroscopic), causing local inflammation. LLQ pain + fever + CT showing sigmoid wall thickening with pericolonic fat stranding = classic diverticulitis. No free air = no perforation yet. Treatment: antibiotics (oral outpatient for mild; IV + bowel rest for severe).
Question 18
A 70-year-old man with known diverticulosis presents with recurrent UTIs caused by E. coli and Bacteroides (colonic flora). He also reports passing air in his urine stream. Which complication of diverticulitis has occurred?
A. Pericolonic abscess rupture into the peritoneum
B. Colovesical fistula
C. Sigmoid stricture causing relative obstruction
D. Sigmoid volvulus from pericolonic adhesions
E. Sigmoid carcinoma arising from chronic diverticular inflammation
Pneumaturia (air in urine) + fecaluria + recurrent polymicrobial UTIs with colonic flora are pathognomonic for a colovesical fistula — a tract connecting the sigmoid colon to the urinary bladder. This is the most common fistulous complication of sigmoid diverticulitis (the sigmoid lies directly adjacent to the bladder in men). Treatment: surgical resection of the involved sigmoid segment with fistula takedown. Colovaginal fistulas occur in women who have had prior hysterectomy.
LO 7 — Colonic Polyps (Q19–Q22)
Question 19
During surveillance colonoscopy of a 62-year-old man, a 2-cm sessile polyp is found in the ascending colon. Histology shows serrated glands extending to the crypt base with lateral growth and crypt dilation. Cytologic dysplasia is absent. Which of the following is the correct classification, and what is the molecular consequence of leaving this lesion unresected?
A. Hyperplastic polyp — no malignant potential; no action needed
B. Tubular adenoma — progresses via APC/beta-catenin pathway to left-sided CRC
C. Sessile serrated adenoma — progresses via microsatellite instability pathway to right-sided CRC
D. Juvenile hamartoma — malignant potential only in polyposis syndrome context
E. Inflammatory polyp — reactive lesion with no neoplastic potential
SSAs look similar to hyperplastic polyps (both have serrated lumens) but differ critically: SSAs have serrated architecture extending to the crypt base with crypt dilation and lateral growth — hyperplastic polyps lack crypt base involvement. SSAs predominate in the right colon and carry malignant potential through the microsatellite instability (MMR deficiency/BRAF mutation) pathway — giving rise to right-sided, mucinous colorectal adenocarcinomas. Lack of cytologic dysplasia does NOT make them safe — they are premalignant. Endoscopic resection is indicated.
Question 20
A 14-year-old boy presents with dark spots on his lips and buccal mucosa. His father had the same pigmentation and died of pancreatic cancer at 50. Endoscopy shows large pedunculated polyps predominantly in the jejunum. Histology of one polyp shows smooth muscle arborizing through the lamina propria, with normal-appearing epithelium. What is the syndrome, and what gene is mutated?
A. Juvenile polyposis syndrome; SMAD4
B. Peutz-Jegher syndrome; STK11
C. Familial adenomatous polyposis; APC
D. Lynch syndrome; MSH2
E. Cowden syndrome; PTEN
The triad: mucocutaneous hyperpigmentation (perioral dark spots) + hamartomatous GI polyps (predominantly small intestine) + positive family history = PJS. The pathognomonic histologic feature is smooth muscle arborizing through the core of the polyp. STK11 (LKB1) is the causative tumor suppressor gene, mutated in ~50% of cases. Patients have significantly elevated risk of GI (pancreatic, small bowel, colorectal, gastric) and extra-GI (breast, lung, ovarian, uterine, cervical) malignancies. Surveillance with regular endoscopy and imaging is essential.
Question 21
A patient with longstanding ulcerative colitis undergoes colonoscopy, which shows multiple raised, erythematous, irregular polypoid lesions scattered throughout the colon among areas of active ulceration. Biopsy of these lesions shows inflamed, regenerating mucosa with no dysplasia. What are these lesions, and what is their significance?
A. Tubular adenomas — require polypectomy
B. Pseudopolyps (inflammatory polyps) — islands of regenerating mucosa; no intrinsic malignant potential
C. Sessile serrated adenomas — premalignant; require aggressive surveillance
D. Hyperplastic polyps — benign; no surveillance needed beyond standard colonoscopy
E. Juvenile polyps — may cause bleeding but no dysplastic risk in adults
Pseudopolyps in UC are NOT true neoplasms — they are islands of regenerating, inflamed mucosa that remain elevated as surrounding mucosa ulcerates away. They have no intrinsic malignant potential themselves. However, their presence confirms active UC, and the underlying UC carries significant cancer risk. Importantly, pseudopolyps can make surveillance colonoscopy challenging (hard to distinguish from dysplastic lesions), which is one reason long-standing UC warrants regular surveillance biopsies throughout the colon.
Question 22
A 67-year-old woman undergoes colonoscopy for colorectal cancer screening. A 3-cm pedunculated polyp is found in the sigmoid colon. Histology shows dysplastic glandular epithelium with tubular and villous architecture mixed, but the basement membrane is intact. What is the correct classification, and which subtype carries the highest malignancy risk?
A. Hyperplastic polyp; villous type has highest risk
B. Hamartomatous polyp; tubular type has highest risk
C. Adenoma (tubulovillous); villous adenoma has highest malignancy risk overall
D. Inflammatory polyp; sessile type has highest risk
E. Sessile serrated adenoma; it always has higher risk than traditional adenomas
This is a tubulovillous adenoma — mixed tubular and villous architecture with dysplasia. Among the traditional adenoma subtypes, malignancy risk correlates with: (1) Villous component (more villous = higher risk), (2) Size (>2 cm significantly elevated risk), (3) High-grade vs. low-grade dysplasia. Tubular adenoma (~5% cancer risk) < Tubulovillous (~20%) < Villous adenoma (~40%). Pure villous adenomas are also classically associated with "villous adenoma syndrome" — profuse watery diarrhea + severe hypokalemia from mucus secretion. This polyp requires complete resection and pathologic assessment of the stalk for invasion.
LO 8 — Colorectal Carcinoma & Familial Syndromes (Q23–Q26)
Question 23
A 28-year-old man undergoes colonoscopy after his father was diagnosed with colorectal carcinoma at age 30. The colonoscopy shows carpet-like covering of the entire colonic mucosa with hundreds of small, flat adenomatous polyps. Genetic testing confirms an APC gene mutation. Without intervention, what is his lifetime risk of developing colorectal carcinoma?
A. 10–15% (similar to Lynch syndrome)
B. 30–40% (moderately elevated)
C. 50% (same as general Lynch syndrome risk)
D. 100% (virtually certain by age 30–40 without colectomy)
E. 5% (only mildly elevated over baseline)
FAP (Familial Adenomatous Polyposis) carries essentially 100% lifetime risk of colorectal carcinoma in untreated patients — usually before age 40, often before 30. The APC mutation leads to thousands of tubular adenomas throughout the colon; with so many lesions, it is a statistical certainty that at least one will progress. Standard management is prophylactic total proctocolectomy in the late teens or early 20s. Yearly sigmoidoscopy begins in puberty for surveillance until surgery. Annual upper endoscopy is also needed for duodenal/gastric polyps (Gardner FAP variant).
Question 24
A 42-year-old woman with Lynch syndrome (MLH1 mutation confirmed) asks about her cancer risks beyond colorectal cancer. Which of the following additional cancers is she at HIGHEST risk for, and why?
A. Breast cancer — BRCA co-mutation is universal in Lynch syndrome
B. Endometrial cancer — microsatellite instability also drives gynecologic malignancy
C. Pancreatic cancer — STK11 mutation in Lynch causes pancreatic ductal adenocarcinoma
D. Hepatocellular carcinoma — MLH1 mutation causes defective DNA repair in hepatocytes
E. Neuroblastoma — DNA mismatch repair is required for neural tissue differentiation
Lynch syndrome causes germline mutations in MMR genes (MLH1, MSH2, MSH6, PMS2), leading to microsatellite instability throughout the body — not just in the colon. The endometrium is particularly susceptible; endometrial cancer is the most common Lynch-associated cancer in women (lifetime risk up to 40-60%). Other Lynch-associated extra-colonic cancers: ovarian, gastric, small bowel, urothelial, biliary. Surveillance: annual gynecologic exam + transvaginal ultrasound + endometrial biopsy, plus consideration of risk-reducing hysterectomy/BSO after childbearing is complete.
Question 25
A 55-year-old man presents with hematochezia and rectal pain. He has a 15-year history of receptive anal intercourse. Anoscopy shows a 2-cm ulcerated mass at the dentate line. Biopsy shows squamous cell carcinoma. Which of the following is most strongly associated with this tumor?
A. Familial adenomatous polyposis (APC mutation)
B. Human papillomavirus (HPV) high-risk strains
C. Inflammatory bowel disease (UC-associated dysplasia)
D. Hereditary non-polyposis colorectal cancer (Lynch syndrome)
E. Clostridium difficile-associated colitis
Squamous cell carcinoma of the anal canal is strongly associated with high-risk HPV infection. The lower third of the anal canal is lined by stratified squamous epithelium, which is susceptible to HPV-driven oncogenesis (E6 inactivates p53; E7 inactivates Rb). Risk factors include receptive anal intercourse, multiple sexual partners, and immunosuppression (HIV). This is analogous to HPV-driven cervical SCC and oropharyngeal SCC. Treatment: Nigro protocol (5-FU + mitomycin-C + radiation) is often curative and sphincter-preserving, making it preferable to surgery.
Question 26
A 58-year-old woman with iron-deficiency anemia undergoes colonoscopy, which reveals a large polypoid mass in the cecum. CT shows no lymph node involvement or distant metastases. Surgical pathology shows adenocarcinoma invading through the muscularis propria into the pericolic fat (T3N0M0). What are the two most important prognostic factors in colorectal adenocarcinoma, and what is her 5-year prognosis?
A. Tumor size and CEA level — good prognosis if CEA normalized after surgery
B. Depth of invasion (T stage) and lymph node metastasis (N stage) — T3N0 has ~70-80% 5-year survival
C. Microsatellite instability status and KRAS mutation — determines chemotherapy eligibility only
D. Tumor location and age of patient — right-sided tumors have universally poor prognosis
E. Degree of differentiation (grade) and tumor size — grade is the single most important factor
The two most critical prognostic factors in CRC are: (1) Depth of wall invasion (T stage) — tumors confined to mucosa/submucosa have excellent prognosis; T3 (through muscularis propria) and T4 (through serosa or into adjacent organs) are worse; (2) Lymph node metastasis (N stage) — the single most powerful predictor. For this T3N0M0 patient (Stage IIA), 5-year survival is approximately 70-80%. Distant metastasis (M stage; usually liver first, then lung) reduces 5-year survival to ~10-15%. MSI status also has prognostic and therapeutic implications (MSI-high tumors respond to immunotherapy).