Definition/General
Introduction:
Small intestinal tuberculosis is a chronic granulomatous infection caused by Mycobacterium tuberculosis
It represents extrapulmonary tuberculosis
It is endemic in developing countries including India
It shows granulomatous inflammation with caseation necrosis.
Origin:
Caused by Mycobacterium tuberculosis complex
Spread by hematogenous route from pulmonary focus
Lymphatic spread from adjacent lymph nodes
Direct ingestion of infected sputum
Results in chronic granulomatous inflammation.
Classification:
Primary intestinal TB: no evidence of pulmonary TB
Secondary intestinal TB: associated with pulmonary TB
Location: ileocecal region most common (85%)
Small bowel involvement: terminal ileum predominantly.
Epidemiology:
High prevalence in India (endemic region)
Young adults most affected (20-40 years)
No gender predilection
Malnutrition and immunosuppression predispose
Associated with HIV coinfection.
Clinical Features
Presentation:
Chronic abdominal pain (most common)
Fever and weight loss
Diarrhea or constipation
Small bowel obstruction
Right iliac fossa mass
Intestinal perforation (rare).
Symptoms:
Right iliac fossa pain (mimics appendicitis)
Constitutional symptoms: fever, night sweats, weight loss
Altered bowel habits
Anorexia and malaise
Abdominal distension
Symptoms of intestinal obstruction.
Risk Factors:
Immunocompromised states: HIV, diabetes, malnutrition
Poverty and overcrowding
Contact with active TB
Corticosteroid therapy
Alcoholism
Previous history of tuberculosis.
Screening:
CT abdomen (bowel wall thickening, lymphadenopathy)
Colonoscopy with biopsy
Tuberculin skin test
Interferon-gamma release assays (IGRA)
Chest X-ray (pulmonary TB)
Histopathological examination.
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Gross Description
Appearance:
Bowel wall thickening and rigidity
Ulcerative lesions with undermined edges
Strictures and scarring
Mesenteric lymphadenopathy
Caseating lymph nodes
Perforation (complications).
Characteristics:
Terminal ileum and ileocecal valve involvement
Transverse ulcers (characteristic)
Skip lesions pattern
Bowel wall thickening up to 2-3 cm
Serosal nodules
Adhesions and matting.
Size Location:
Terminal ileum (85% cases)
Ileocecal valve commonly involved
Right colon extension
Jejunal involvement (10-15%)
Multiple sites possible
Segmental distribution.
Multifocality:
Ileocecal region predilection
Skip lesions characteristic
Multifocal involvement common
Mesenteric lymph node involvement
Peritoneal seedling possible.
Microscopic Description
Histological Features:
Epithelioid granulomas with caseation necrosis
Langhans giant cells
Chronic inflammation
Transmural involvement
Mucosal ulceration
Fibrosis and scarring.
Cellular Characteristics:
Epithelioid cells (activated macrophages)
Langhans-type giant cells
Lymphocytes and plasma cells
Caseation necrosis (pathognomonic)
Neutrophilic infiltrate (secondary infection)
Eosinophils may be present.
Architectural Patterns:
Well-formed granulomas
Transmural inflammation
Mucosal destruction and ulceration
Submucosal fibrosis
Lymphatic obstruction
Neural involvement (myenteric plexus).
Grading Criteria:
Granuloma maturity: well-formed vs poorly-formed
Caseation presence: typical vs atypical
Bacterial load: paucibacillary vs multibacillary
Inflammatory activity: active vs healing.
Immunohistochemistry
Positive Markers:
CD68 (macrophages/epithelioid cells)
CD163 (M2 macrophages)
Lysozyme (macrophages)
CD3 (T-lymphocytes)
CD20 (B-lymphocytes in mantle).
Negative Markers:
Cytokeratins (excludes epithelial cells)
CD30 (excludes lymphoma)
S-100 (excludes nerve sheath tumors)
Melanin (excludes melanoma).
Diagnostic Utility:
Confirms macrophage nature of epithelioid cells
Demonstrates granulomatous inflammation
Excludes other causes of granulomas
Assesses inflammatory cell composition
Identifies mycobacteria when combined with special stains.
Molecular Subtypes:
Classical granulomatous TB
Atypical presentations: minimal granulomas
Drug-resistant TB: altered inflammatory response
HIV-associated TB: reduced granuloma formation.
Molecular/Genetic
Genetic Mutations:
Host genetic factors: HLA associations, cytokine gene polymorphisms
Mycobacterial drug resistance: rpoB, katG, inhA genes
MDR-TB markers: resistance to rifampin and isoniazid
XDR-TB markers: additional fluoroquinolone resistance.
Molecular Markers:
Interferon-γ production
TNF-α elevation
IL-12 and IL-18 upregulation
Th1 immune response markers
Bacterial DNA/RNA detection.
Prognostic Significance:
Early diagnosis: better treatment outcomes
Drug resistance: worse prognosis
Immunocompromised hosts: higher mortality
Complications: perforation, obstruction affect prognosis.
Therapeutic Targets:
Anti-TB therapy: DOTS regimen (6 months)
First-line drugs: rifampin, isoniazid, ethambutol, pyrazinamide
MDR-TB treatment: second-line drugs
Surgical intervention: complications
Nutritional support.
Differential Diagnosis
Similar Entities:
Crohn disease
Adenocarcinoma
Lymphoma
Other granulomatous infections
Sarcoidosis
Foreign body reaction.
Distinguishing Features:
TB: caseating granulomas, AFB positive, endemic area
Crohn: non-caseating granulomas, skip lesions, transmural
Cancer: malignant cells, no granulomas
Other infections: specific organisms identified.
Diagnostic Challenges:
Distinguishing from Crohn disease (both show granulomas)
Identifying mycobacteria (paucibacillary cases)
Culture confirmation (slow growth)
Correlation with clinical presentation
Drug resistance testing.
Rare Variants:
Hypertrophic TB
Ulcerative TB
Ulcerohypertrophic TB
Fibrous stricture (healed TB)
Miliary TB (disseminated form).
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 biopsy/resection from [terminal ileum/jejunum], [number] fragments
Diagnosis
Chronic granulomatous inflammation consistent with tuberculosis
Granulomas
Epithelioid granulomas with caseation necrosis and Langhans giant cells
Distribution
Transmural involvement with mucosal ulceration
Special Stains
Ziehl-Neelsen stain: [positive/negative] for acid-fast bacilli
Associated Changes
Chronic inflammation with fibrosis and mucosal destruction
Molecular Studies
TB PCR: [positive/negative/pending]
Mycobacterial culture: [pending/positive/negative]
Drug susceptibility: [pending if culture positive]
Recommendations
Clinical correlation, anti-tubercular therapy, culture confirmation
Final Diagnosis
Small intestinal tuberculosis with chronic granulomatous inflammation