A 46-year-old woman comes to the emergency department because of intermittent abdominal pain and vomiting for 2 days. The abdominal pain is colicky and diffuse. The patient's last bowel movement was 3 days ago. She has had multiple episodes of upper abdominal pain that radiates to her scapulae and vomiting over the past 3 months; her symptoms subsided after taking ibuprofen. She has coronary artery disease, type 2 diabetes mellitus, gastroesophageal reflux disease, and osteoarthritis of both knees. Current medications include aspirin, atorvastatin, rabeprazole, insulin, and ibuprofen. She appears uncomfortable. Her temperature is 39°C (102.2°F), pulse is 111/min, and blood pressure is 108/68 mm Hg. Examination shows dry mucous membranes. The abdomen is distended and tympanitic with diffuse tenderness; bowel sounds are high-pitched. Rectal examination shows a collapsed rectum. Her hemoglobin concentration is 13.8 g/dL, leukocyte count is 14,400/mm3, and platelet count is 312,000/mm3. An x-ray of the abdomen is shown. Which of the following is the most likely cause of this patient's findings?

Colonic diverticular inflammation

A 41-year-old male who takes NSAIDs regularly for his chronic back pain develops severe abdominal pain worse with eating. Upper endoscopy is performed and the medical student asks the supervising physician how the histological differentiation between a gastric ulcer and erosion is made. Which of the following layers of the gastric mucosa MUST be breached for a lesion to be considered an ulcer?

Epithelium, lamina propria, muscularis mucosa

Epithelium, lamina propria, muscularis mucosa, submucosa, and adventitia

Epithelium, lamina propria, muscularis mucosa, and submucosa

A 52-year-old man, with a history of alcoholism, presents with loss of appetite, abdominal pain, and fever for the past 24 hours. He says he consumed 12 beers and a bottle of vodka 2 days ago. He reports a 19-year history of alcoholism. His blood pressure is 100/70 mm Hg, pulse is 100/min, respirations are 20/min, and oxygen saturation is 99% on room air. Laboratory findings are significant for the following: Sodium 137 mEq/L Potassium 3.4 mEq/L Alanine aminotransferase (ALT) 230 U/L Aspartate aminotransferase (AST) 470 U/L Which of the following histopathologic findings would most likely be found on a liver biopsy of this patient?

Cytoplasmic inclusion bodies with keratin

Positive periodic acid-Schiff stain

A 25-year-old woman presents to her primary care physician complaining of several months of diarrhea. She has also had crampy abdominal pain. She has tried modifying her diet without improvement. She has many watery, non-bloody bowel movements per day. She also reports feeling fatigued. The patient has not recently traveled outside of the country. She has lost 10 pounds since her visit last year, and her BMI is now 20. On exam, she has skin tags and an anal fissure. Which of the following would most likely be seen on endoscopy and biopsy?

Focal ulcerations with granuloma

Diffuse, non-focal ulcerations with granuloma

Diffuse, non-focal ulcerations without granuloma

Pseudopolyps and continuous mucosal involvement

Friable mucosa with pinpoint hemorrhages

Diverticular disease for USMLE Step 3: High-Yield Pathology Lessons

Overview & Types - Outpouching Problems

Diverticulosis: Uninflamed, asymptomatic outpouchings (pseudodiverticula).
Diverticulitis: Inflammation of diverticula, causing LLQ pain, fever.
True vs. False Diverticula:
- False (e.g., Colonic): Herniation of mucosa & submucosa through the muscularis propria. Most common.
- True (e.g., Meckel's): Includes all three gut wall layers.
Location: Sigmoid colon is the most common site due to high intraluminal pressure.

Diverticulosis vs. Diverticulitis

⭐ Diverticular bleeding is the most common cause of acute lower GI bleeding in adults.

Pathophysiology - Pressure Cooker Colon

Etiology: Chronic constipation, often from a low-fiber diet, leads to increased straining and segmented colonic contractions.
Mechanism: Results in ↑ intraluminal pressure, forcing the herniation (pulsion) of mucosa and submucosa.
- Herniation occurs through natural weak points in the muscularis propria, specifically where the vasa recta (nutrient arteries) penetrate.

Colonic Diverticula Formation and Vasa Recta

⭐ Sigmoid Colon Predilection: The sigmoid is the most common site (>90%). According to the Law of Laplace ($P \propto 1/r$), its narrower diameter generates the highest intraluminal pressure.

Clinical Presentation - Belly Aches & Bleeds

Diverticulosis: Often asymptomatic. The hallmark is painless hematochezia-sudden, massive, maroon-colored rectal bleeding that typically stops spontaneously. May have mild, intermittent cramping.
Diverticulitis: Presents as a steady, deep LLQ abdominal pain, fever, anorexia, nausea, and vomiting. Altered bowel habits (constipation or diarrhea) are common. On exam, find localized LLQ tenderness.

⭐ Exam Tip: While inflammation (-itis) is most common in the left-sided sigmoid colon, significant bleeding (-osis) more frequently originates from right-sided colonic diverticula.

Diagnosis - Seeing the Sacs

Diverticulosis: Typically an incidental finding on screening colonoscopy, revealing multiple colonic outpouchings (diverticula).
Acute Diverticulitis:
- Abdominal/pelvic CT with contrast is the best initial and most accurate test.
- Key findings: Localized bowel wall thickening (>4 mm), pericolic fat stranding, abscess, or extraluminal air/fluid.

CT scan of acute diverticulitis with fat stranding

⭐ ⚠️ In acute diverticulitis, avoid colonoscopy and barium enema. They are contraindicated due to the high risk of perforation.

Management & Complications - Fixing the Flaws

Complications: 📌 FOPA
- Fistula (Colovesical → pneumaturia)
- Obstruction
- Perforation (→ peritonitis)
- Abscess (most common)

⭐ Recurrent uncomplicated diverticulitis or a single complicated episode often prompts consideration for elective sigmoid colectomy to prevent future attacks and severe complications.

High‑Yield Points - ⚡ Biggest Takeaways

Diverticulosis is typically asymptomatic and linked to a low-fiber diet; diverticulitis presents with LLQ pain and fever.

The sigmoid colon is the most common site due to high intraluminal pressure.

These are false (pulsion) diverticula, occurring at weak points where vasa recta penetrate the muscularis propria.

Painless rectal bleeding is a complication of diverticulosis, not diverticulitis.

CT scan with contrast is the best test for acute diverticulitis; avoid colonoscopy in the acute setting due to perforation risk.

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