ABPath Gastrointestinal Pathology 2

Question 1

Whipple disease is caused by which organism and is confirmed by which stain?

Accepted Answer

Tropheryma whipplei; PAS stain

Answer

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?

Accepted Answer

Villous atrophy, crypt hyperplasia, intraepithelial lymphocytosis

Answer

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?

Accepted Answer

KIT (CD117)

Answer

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?

Accepted Answer

Tumor size >2 cm

Answer

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:

Accepted Answer

Volcanic eruption pattern with fibrinopurulent caps over crypts

Answer

C. difficile colitis shows the classic 'volcano lesion' — a pseudomembrane of fibrin, mucin, and neutrophils erupting from damaged crypts like a volcanic plume.

American Board of Pathology (ABPath) Practice Test

American Board of Pathology (ABPath) Practice Test

ABPath Gastrointestinal Pathology 2