Definition/General
Introduction:
Small intestinal adenoma is a benign epithelial neoplasm with dysplastic epithelium
It represents premalignant lesions with malignant potential
It accounts for 25-30% of small bowel tumors
It shows adenoma-carcinoma sequence similar to colorectal adenomas.
Origin:
Arises from intestinal epithelium through dysplastic transformation
Results from accumulation of genetic mutations
APC pathway activation is key early event
Associated with chromosomal instability
May progress to adenocarcinoma (5-10% cases).
Classification:
Histological types: tubular adenoma (75-80%)
Tubulovillous adenoma (15-20%)
Villous adenoma (5%)
Dysplasia grade: low-grade dysplasia
High-grade dysplasia
Location: duodenal, jejunal, ileal.
Epidemiology:
Rare lesions (<1% of GI adenomas)
Male predominance (2:1 ratio)
Peak incidence: 50-70 years
Duodenal adenomas most common (70%)
FAP association (30-90% of FAP patients)
Higher incidence in Western countries.
Clinical Features
Presentation:
Often asymptomatic (small adenomas)
GI bleeding (iron deficiency anemia)
Abdominal pain
Intestinal obstruction (large adenomas)
Intussusception (rare)
Symptoms of associated syndromes (FAP, Lynch syndrome).
Symptoms:
Occult GI bleeding (iron deficiency)
Crampy abdominal pain
Change in bowel habits
Small bowel obstruction (large lesions)
Symptoms of malabsorption (villous adenomas)
Constitutional symptoms (weight loss, fatigue).
Risk Factors:
Familial adenomatous polyposis (FAP)
Lynch syndrome
Peutz-Jeghers syndrome
Advanced age (>50 years)
Male sex
Family history of colorectal cancer
Diet and lifestyle factors.
Screening:
Upper endoscopy (duodenal adenomas)
Capsule endoscopy
Double-balloon enteroscopy
CT enterography
Genetic testing (familial syndromes)
Colonoscopy (associated colorectal adenomas).
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Gross Description
Appearance:
Polypoid lesions (most common)
Sessile or pedunculated
Smooth or lobulated surface
Soft consistency
Color: pink to red
Surface ulceration possible (large lesions).
Characteristics:
Well-demarcated lesions
Villous architecture (finger-like projections)
Tubular pattern (rounded glands)
Surface may be friable (villous type)
Pedunculated (smaller lesions)
Sessile (larger lesions).
Size Location:
Duodenum (70% cases): periampullary region common
Jejunum (20%)
Ileum (10%)
Size range: 0.5-10 cm (average 2-3 cm)
Solitary (sporadic)
Multiple (FAP).
Multifocality:
Solitary lesions (sporadic cases)
Multiple adenomas (FAP: 30-90% patients)
Carpet lesions (extensive villous adenomas)
Associated colorectal adenomas
Synchronous adenocarcinoma (5% cases).
Microscopic Description
Histological Features:
Dysplastic epithelium with architectural distortion
Tubular or villous architecture
Pseudostratified nuclei
Increased mitotic activity
Mucin depletion
Intact basement membrane (benign).
Cellular Characteristics:
Columnar epithelial cells with dysplastic features
Enlarged, hyperchromatic nuclei
Nuclear pseudostratification
Prominent nucleoli
Mitotic figures above crypt base
Goblet cell reduction.
Architectural Patterns:
Tubular pattern: rounded, back-to-back glands
Villous pattern: finger-like projections
Tubulovillous: mixed architecture
Surface maturation (low-grade)
Loss of polarity (high-grade).
Grading Criteria:
Low-grade dysplasia: mild nuclear atypia, preserved polarity
High-grade dysplasia: marked nuclear atypia, loss of polarity, increased mitoses
Architectural criteria: tubular vs villous components
Surface changes: maturation vs atypia.
Immunohistochemistry
Positive Markers:
CDX2 (intestinal differentiation)
CK20 (intestinal epithelium)
Villin (intestinal brush border)
Ki-67 (increased proliferation)
p53 (high-grade dysplasia)
β-catenin (APC pathway).
Negative Markers:
CK7 (usually negative in small bowel)
TTF-1 (excludes lung origin)
CDX2 loss (high-grade dysplasia)
Chromogranin A (excludes carcinoid).
Diagnostic Utility:
Confirms intestinal epithelial origin
Assesses dysplasia grade (p53, Ki-67)
Evaluates APC pathway (β-catenin)
Distinguishes from other epithelial lesions
Identifies high-risk features.
Molecular Subtypes:
Conventional adenomas: APC pathway, chromosomal instability
Serrated adenomas: KRAS mutations, microsatellite instability
FAP-associated: germline APC mutations.
Molecular/Genetic
Genetic Mutations:
APC mutations (70-80% sporadic, 100% FAP)
KRAS mutations (40-50%)
TP53 mutations (high-grade dysplasia)
PIK3CA mutations
SMAD4 mutations (advanced adenomas).
Molecular Markers:
Wnt pathway activation
β-catenin nuclear accumulation
p53 overexpression (high-grade)
Loss of heterozygosity (18q, 17p)
Chromosomal instability.
Prognostic Significance:
Size >1 cm: increased malignant risk
Villous architecture: higher malignant potential
High-grade dysplasia: 10-15% cancer risk
Location: duodenal adenomas higher cancer risk.
Therapeutic Targets:
Endoscopic resection: complete excision
COX-2 inhibitors: chemoprevention
Surveillance endoscopy
Surgical resection (large lesions, high-grade dysplasia)
Genetic counseling (familial syndromes).
Differential Diagnosis
Similar Entities:
Hyperplastic polyp
Inflammatory polyp
Peutz-Jeghers polyp
Juvenile polyp
Adenocarcinoma
Carcinoid tumor.
Distinguishing Features:
Adenoma: true dysplasia, APC mutations
Hyperplastic: no dysplasia, serrated architecture
PJ polyp: smooth muscle core, STK11 mutations
Adenocarcinoma: invasion through basement membrane.
Diagnostic Challenges:
Distinguishing high-grade dysplasia from invasive carcinoma
Assessing completeness of excision
Identifying associated familial syndromes
Evaluating malignant potential
Correlation with endoscopic findings.
Rare Variants:
Serrated adenoma
Traditional serrated adenoma
Sessile serrated adenoma
Adenoma with carcinoid features
Adenoma in Brunner gland.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Small bowel polyp from [duodenum/jejunum/ileum], [size] cm
Diagnosis
[Tubular/tubulovillous/villous] adenoma with [low/high]-grade dysplasia
Classification
Histological type: [percentage] tubular, [percentage] villous
Histological Features
Dysplastic epithelium with [architectural pattern] and [dysplasia grade]
Size and Architecture
Size: [X] cm, architecture: [tubular/villous percentage]
Dysplasia Grade
Dysplasia: [low-grade/high-grade]
Margins
Excision margins: [complete/incomplete/cannot be assessed]
Special Studies
CDX2: [positive], Ki-67: [percentage]
p53: [result if performed]
[other study]: [result]
Recommendations
Surveillance endoscopy recommended, consider genetic evaluation if multiple polyps
Final Diagnosis
Small intestinal [type] adenoma with [grade] dysplasia