Abdominal TB

Introduction

Abdominal Tuberculosis (TB) is a significant form of extrapulmonary tuberculosis (EPTB) in children. It accounts for a variable proportion of EPTB cases (approximately 6.4% in some series) but presents a major diagnostic challenge due to its non-specific clinical features which mimic other gastrointestinal pathologies. It can involve the gastrointestinal tract, peritoneum, mesenteric lymph nodes, and solid viscera (liver, spleen, pancreas). Approximately one-third of patients may have involvement of more than one of these sites.

Etiopathogenesis

The causative agent is Mycobacterium tuberculosis (and rarely M. bovis or M. avium complex). The modes of infection include:

1. Ingestion: Swallowing of infected sputum (in patients with active pulmonary TB) or ingestion of unpasteurized milk (historically associated with M. bovis). The bacilli lodge in the submucosal Peyer's patches of the small intestine.
2. Hematogenous Spread: Dissemination from a primary focus in the lungs during the phase of primary bacteremia.
3. Direct Extension: Spread from adjacent infected organs (e.g., fallopian tubes) or rupture of a caseous abdominal lymph node.

Clinical Classifications

Abdominal TB can be classified based on the site of involvement:

1. Intestinal TB: Most commonly affects the ileocecal region. Can be Ulcerative (common in malnutrition/wasting), Hypertrophic (obstructive mass), or Ulcero-hypertrophic.
2. Peritoneal TB: Can be Wet (Ascitic form), Dry (Plastic form with adhesions), or Fibrotic (encysted).
3. Tuberculous Lymphadenitis: Mesenteric or retroperitoneal lymph node involvement.
4. Visceral TB: Involvement of liver, spleen, or pancreas (often part of disseminated/miliary TB).

Clinical Features

The onset is usually insidious. Symptoms may be constitutional or abdominal.

• Systemic Symptoms: Low-grade fever, anorexia, significant weight loss or failure to gain weight, and night sweats.
• Abdominal Symptoms:
  • Pain: Chronic or recurrent colicky abdominal pain is common.
  • Distension: Due to ascites or intestinal obstruction.
  • Bowel Habits: Alternating diarrhea and constipation (common in enteric TB).
  • Vomiting: May indicate subacute intestinal obstruction.
• Physical Signs:
  • "Doughy" Abdomen: Characteristic of the plastic/adhesive form of peritonitis.
  • Ascites: Usually high protein, exudative.
  • Mass: Irregular masses may be palpated (rolled-up omentum, matted lymph nodes, or ileocecal mass).
  • Organomegaly: Hepatomegaly or splenomegaly.

Diagnostic Approach

Diagnosis requires a high index of suspicion and a multi-modality approach as no single test is pathognomonic.

1. Imaging Modalities

Radiology plays a pivotal role in diagnosis.

A. Ultrasonography (USG) Abdomen This is the recommended initial modality of choice.

• Findings:
  • Lymphadenopathy: Matted nodes, often with central hypoechogenicity (necrosis) and peripheral vascularity.
  • Ascites: Often loculated or septated with fine strands (fibrin).
  • Thickening: Bowel wall thickening (uniform and concentric), omental thickening ("omental cake"), or peritoneal thickening.
• Note: Small (<1 cm) non-matted nodes are common in children with functional abdominal pain and should not be misdiagnosed as TB without other evidence.

B. Contrast-Enhanced CT (CECT) / CT Enterography CT provides better anatomical detail and is useful for visualizing the bowel and mesentery. Characteristic Imaging Findings (Box 1, NTEP Guidelines 2022):

• Lymph Nodes: Necrotic abdominal nodes with peripheral rim enhancement and conglomerate mass formation.
• Bowel: Uniform concentric bowel thickening, short strictures (<3 cm), contracted and "pulled-up" caecum, distorted ileocecal angle (often obtuse).
• Mesentery: Mesenteric thickening >15 mm.
• Peritoneum: Caked omentum, loculated ascites.

C. Chest X-ray Useful to look for concomitant pulmonary TB (active or healed) or pleural effusion, which supports the diagnosis.

2. Microbiological and Pathological Diagnosis

Confirming the diagnosis is difficult due to the paucibacillary nature of the disease.

A. Ascitic Fluid Analysis

• Biochemistry: Exudative (Protein >3 g/dL), Low SAAG (Serum-Ascites Albumin Gradient <1.1).
• Cytology: Lymphocytic predominance.
• Adenosine Deaminase (ADA): High levels (>30-40 IU/L) are supportive but can be falsely positive in other conditions; hence not solely relied upon.
• Microbiology: Smear for AFB and Culture usually have a low yield in ascitic fluid.

B. Tissue Diagnosis (Gold Standard) Obtaining tissue via laparoscopy, endoscopy (colonoscopy), or USG/CT-guided biopsy is the most reliable method.

• Sites: Peritoneal biopsy, lymph node aspiration/biopsy, or intestinal biopsy (from ulcers/mass).
• Peritoneoscopy: Visual findings of tubercles (whitish miliary nodules) on the peritoneum have high sensitivity (93%) and specificity (98%).
• Tests on Tissue:
  • Histopathology: Caseating granulomas (epithelioid cells, Langhans giant cells).
  • NAAT (GeneXpert/TrueNat): Should be performed on the biopsy specimen/pus for rapid confirmation and Rifampicin resistance testing.
  • Culture (MGIT): Definitive for diagnosis and Drug Susceptibility Testing (DST).

Differential Diagnosis

• Crohn's Disease: Differentiated by skip lesions, longitudinal ulcers, transmural involvement, and non-caseating granulomas.
• Malignancy: Lymphoma (abdominal Burkitt's) or peritoneal carcinomatosis.
• Gastrointestinal Infections: Yersinia, Giardiasis, or chronic Amoebiasis.

Treatment

The management follows the principles of standard anti-tubercular therapy.

1. Medical Management

• Regimen: As per NTEP 2022 guidelines for drug-sensitive TB.
  • Intensive Phase (2 months): Isoniazid (H), Rifampicin (R), Pyrazinamide (Z), and Ethambutol (E).
  • Continuation Phase (4 months): Isoniazid (H), Rifampicin (R), and Ethambutol (E).
  • Total Duration: 6 months.
• Monitoring: Clinical assessment of weight gain, resolution of fever, and regression of ascites/masses.

2. Surgical Management

Surgery is conservative and reserved for complications:

• Intestinal Obstruction: Acute or subacute obstruction not responding to conservative management.
• Perforation: Peritonitis due to bowel perforation.
• Abscess: Drainage of large abscesses.
• Biopsy: Diagnostic laparoscopy if non-invasive tests are inconclusive.

Complications

• Intestinal obstruction (strictures/adhesions).
• Malabsorption syndrome.
• Enterocutaneous fistulae.
• Infertility (due to secondary involvement of fallopian tubes in females).