ABPath Gastrointestinal Pathology 2 — Questions and Answers
Question 1: Whipple disease is caused by which organism and is confirmed by which stain?
- Yersinia enterocolitica; Gram stain
- Tropheryma whipplei; PAS stain (Correct answer)
- Mycobacterium avium; AFB stain
- Giardia lamblia; H&E
Correct answer: Tropheryma whipplei; PAS stain
Whipple disease is caused by Tropheryma whipplei; foamy macrophages containing the organism in the lamina propria stain positive with PAS (periodic acid-Schiff).
Question 2: Celiac disease (gluten-sensitive enteropathy) is characterized by which histologic triad?
- Granulomas, crypt hyperplasia, goblet cell loss
- Villous atrophy, crypt hyperplasia, intraepithelial lymphocytosis (Correct answer)
- Transmural inflammation, skip lesions, fissuring ulcers
- Mucosal erosions, pseudopolyps, crypt abscesses
Correct answer: Villous atrophy, crypt hyperplasia, intraepithelial lymphocytosis
The classic triad of celiac disease is villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis (>25 IELs per 100 enterocytes) on duodenal biopsy.
Question 3: Gastrointestinal stromal tumors (GISTs) are MOST commonly driven by activating mutations in which gene?
- KRAS
- KIT (CD117) (Correct answer)
- BRAF
- HER2
Correct answer: KIT (CD117)
Approximately 80–85% of GISTs harbor activating mutations in KIT (CD117), with PDGFRA mutations in most KIT-wild-type cases; imatinib targets these kinases.
Question 4: Which feature of appendiceal carcinoid (well-differentiated neuroendocrine tumor) is MOST strongly associated with metastatic potential?
- Location at the appendiceal tip
- Tumor size >2 cm (Correct answer)
- Presence of mucin
- Mitotic rate <2 per 10 HPF
Correct answer: Tumor size >2 cm
Appendiceal carcinoids >2 cm have a significantly higher risk of metastasis (up to 30%), while tumors <2 cm rarely metastasize (<2%).
Question 5: Pseudomembranous colitis caused by Clostridioides difficile is histologically characterized by:
- Transmural neutrophilic infiltrate
- Volcanic eruption pattern with fibrinopurulent caps over crypts (Correct answer)
- Non-caseating granulomas
- Intraepithelial lymphocytosis
Correct answer: Volcanic eruption pattern with fibrinopurulent caps over crypts
C. difficile colitis shows the classic 'volcano lesion' — a pseudomembrane of fibrin, mucin, and neutrophils erupting from damaged crypts like a volcanic plume.
Question 6: Primary sclerosing cholangitis (PSC) is MOST strongly associated with which bowel disease?
- Crohn disease (small bowel)
- Celiac disease
- Ulcerative colitis (Correct answer)
- Microscopic colitis
Correct answer: Ulcerative colitis
PSC is associated with ulcerative colitis in approximately 70–80% of cases; patients with both conditions have elevated risk for cholangiocarcinoma and colorectal cancer.
ABPath Gastrointestinal Pathology 2
Whipple disease is caused by which organism and is confirmed by which stain?