Owl's eye: large basophilic intranuclear inclusion + smaller cytoplasmic inclusions
N/A
Key histologic finding
Multinucleated giant squamous cells with 3 M's at ulcer margin
Cytomegalic cells (2–4× enlarged) with owl's eye nuclei at ulcer base
Pseudohyphae + budding yeast (not true hyphae)
Special stain
H&E (Cowdry A inclusions visible)
H&E (owl's eye visible)
GMS (Gomori methenamine silver); also PAS stain
⚠ Biopsy tip: For HSV, sample the ulcer margin (squamous cells with Cowdry A inclusions). For CMV, sample the ulcer base (endothelial cells/fibroblasts with owl's eye nuclei). This distinction is tested directly.
LO 2 — GERD
Aspect
Details
Primary mechanism
Transient LES (lower esophageal sphincter) relaxation — not just decreased LES tone
⚠ GERD histology: basal cell hyperplasia >15% epithelial thickness + elongated papillae >50–60% into epithelium = hallmarks even without visible inflammation. Eosinophils may be present but are not required.
LO 3 — Barrett's Esophagus
⚠️ On-Exam: Barrett's requires BOTH endoscopic (salmon tongues) AND histologic (goblet cells) criteria
Feature
Barrett's Esophagus
Macroscopic appearance
Salmon-colored tongues of mucosa extending above the GEJ; irregular Z-line on endoscopy
Histologic hallmark
Goblet cells (columnar intestinal metaplasia) — sine qua non; columnar epithelium replaces normal squamous
Diagnosis requires
Both endoscopic criteria (salmon tongues above GEJ) AND histologic criteria (goblet cells on biopsy)
⚠ Erosion vs Ulcer distinction: Erosion = partial-thickness mucosal loss (muscularis mucosae intact). Ulcer = full-thickness through muscularis mucosae into submucosa or deeper. Tested frequently in clinical vignettes.
LO 6 — H. pylori vs Autoimmune Gastritis
⚠️ On-Exam: Know acid levels, gastrin, location, stain, and sequelae for each type
Feature
H. pylori Gastritis
Autoimmune Gastritis
Location
Gastric antrum (antrum-predominant)
Body and fundus (corpus-predominant)
Antrum involvement
Yes (antrum predominant)
No — antrum SPARED (G cells remain intact)
Inflammatory cells
Neutrophils + plasma cells (mixed acute and chronic)
Lymphocytes (CD4+ T-cell–mediated destruction of parietal cells)
WHO Class I carcinogen (definite human carcinogen)
Gram-negative; spiral / helical (curved rod)
Urease-positive → converts urea → NH₃ → ↑ local pH → enables colonization; basis of urea breath test and CLO test
USMLE-Style Practice Questions — Answers Shown
1. A 48-year-old HIV-positive man presents with dysphagia and odynophagia. Endoscopy shows a linear ulcer in the mid-esophagus. Biopsy taken from the ulcer base reveals enlarged cells with large basophilic intranuclear inclusions surrounded by a clear halo ("owl's eye"). Which organism is responsible?
A. HSV-1 B. CMV C. Candida albicans D. H. pylori E. EBV
B. CMV. Owl's eye intranuclear inclusions in endothelial cells/fibroblasts at the ulcer base = CMV esophagitis. Linear ulcers are characteristic of CMV. HSV shows Cowdry A inclusions in squamous cells at the ulcer margin (punched-out ulcers). Candida shows pseudohyphae. (LO 1)
2. A 58-year-old man with 25 years of heartburn undergoes surveillance endoscopy revealing salmon-colored tongues of mucosa extending 3 cm above the gastroesophageal junction. Biopsy confirms columnar epithelium with goblet cells. What is the primary cancer risk of this condition?
A. Squamous cell carcinoma of the esophagus B. Adenocarcinoma of the esophagus C. Gastric adenocarcinoma D. Esophageal MALT lymphoma E. No malignant potential
B. Adenocarcinoma of the esophagus. Salmon tongues + goblet cells (intestinal metaplasia) = Barrett's esophagus. Requires both endoscopic AND histologic criteria. Barrett's is a precursor to esophageal adenocarcinoma (not SCC), progressing through low-grade → high-grade dysplasia → invasive carcinoma. (LO 3)
3. A 65-year-old man with a 40-pack-year history and chronic alcohol use presents with progressive dysphagia. Endoscopy reveals a mid-esophageal mass. Biopsy shows keratin pearls and intercellular bridges. Which IHC profile is expected?
A. p63+, CK5/6+, mucin− B. CK7+, CDX2+, mucin+ C. CD117+, DOG1+, desmin− D. CD20+, BCL2+ E. Chromogranin+, synaptophysin+
A. p63+, CK5/6+, mucin−. Keratin pearls + intercellular bridges = squamous cell carcinoma. Mid-esophagus + alcohol + tobacco = classic SCC setting. SCC is p63+ and CK5/6+ (squamous markers), mucin−. Adenocarcinoma (lower esophagus/GEJ, GERD/Barrett's) would be mucin+ with glands. (LO 3)
4. A 52-year-old woman has fatigue and macrocytic anemia. Labs: ↓ gastric acid, ↑↑ serum gastrin, anti-parietal cell antibodies (+), B12 deficient. Biopsy shows lymphocytic infiltrate in the gastric body and fundus with antrum sparing. What is the pathophysiology of her anemia?
A. H. pylori → mucosal bleeding → iron deficiency B. Parietal cell destruction → ↓ intrinsic factor → ↓ B12 absorption C. Antral G-cell hyperplasia → ↑ gastrin → folate deficiency D. Intestinal metaplasia → ↓ iron absorption E. NSAIDs → chronic occult bleeding → iron deficiency
B. Parietal cell destruction → ↓ intrinsic factor → ↓ B12 absorption. Autoimmune gastritis: T-cell–mediated destruction of parietal cells → loss of intrinsic factor → B12 malabsorption → megaloblastic (pernicious) anemia. Antrum sparing + ↑↑ gastrin + anti-parietal cell Ab confirm autoimmune gastritis. (LO 6)
5. A 50-year-old man with a known duodenal ulcer suddenly develops severe "board-like" rigid abdomen. Upright CXR shows free air under the diaphragm. Which complication occurred, and which structure is classically eroded by a posterior duodenal ulcer causing hemorrhage?
A. Perforation; gastroduodenal artery B. Hemorrhage; splenic artery C. Pyloric obstruction; left gastric artery D. Perforation; inferior mesenteric artery E. Hemorrhage; superior mesenteric vein
A. Perforation; gastroduodenal artery. Free air under diaphragm + acute peritonitis = perforation (P in PHP). Posterior duodenal ulcers classically erode the gastroduodenal artery → massive hemorrhage. PHP = Perforation, Hemorrhage (most common complication), Pyloric obstruction (from scarring/edema). (LO 8)
6. Gastric biopsy shows cells with a rim of mucin pushing the nucleus to the cell periphery ("signet ring" cells). The stomach is diffusely thickened and non-distensible on imaging ("leather bottle"). Which Lauren classification type is this, and what is the prognosis?
A. Intestinal type; relatively better prognosis B. Diffuse type; poor prognosis C. Intestinal type; poor prognosis D. Diffuse type; relatively better prognosis E. Mixed type; intermediate prognosis
B. Diffuse type; poor prognosis. Signet ring cells + linitis plastica (leather bottle stomach) = diffuse-type gastric carcinoma. Diffuse type: worldwide distribution, younger (<50 yo), equal M:F, associated with CDH1 (E-cadherin) mutation, poor prognosis. Intestinal type: glands/goblet cells, antrum, older males, high-incidence areas (Japan), better prognosis. (LO 10)
7. A 60-year-old presents with a 4-cm submucosal gastric mass. Biopsy shows spindle cells. IHC: CD117+, DOG1+, desmin−, S-100−. Which mutation drives this tumor, and what is the first-line targeted therapy?
A. BRAF V600E; vemurafenib B. BCR-ABL; imatinib C. c-KIT gain-of-function; imatinib D. EGFR amplification; erlotinib E. HER2 amplification; trastuzumab
C. c-KIT gain-of-function; imatinib. Submucosal spindle cell tumor + CD117 (c-KIT)+ + DOG1+ = GIST (gastrointestinal stromal tumor), arising from interstitial cells of Cajal. Most common in the stomach. c-KIT gain-of-function mutation → constitutively active tyrosine kinase → treated with imatinib (Gleevec). Prognosis determined by mitotic rate + tumor size. (LO 11)
8. A 64-year-old with known H. pylori infection is found on endoscopy to have a low-grade B-cell gastric lymphoma that histologically resembles chronic gastritis. What is the most appropriate first-line treatment for early-stage low-grade disease?
A. R-CHOP chemotherapy B. Total gastrectomy C. H. pylori eradication (triple therapy) D. Radiation therapy alone E. Rituximab monotherapy
C. H. pylori eradication (triple therapy). Low-grade gastric MALT lymphoma is antigen-driven by H. pylori. In early-stage disease, eradication of H. pylori removes the proliferative stimulus → complete remission. The stomach is the #1 site of extranodal lymphoma (55%). High-grade or refractory disease requires chemotherapy. (LO 12)