Pathology of Tuberculosis

Questions and Answers

What is a characteristic feature of tuberculous ulcers in the terminal ileum?

They are arranged longitudinally

They have undermined edges (correct)

They have sharp edges

They have everted edges

What is the primary site of infection in primary intestinal tuberculosis?

Mesentery

Caecum

Payer's patches (correct)

Terminal ileum

What is the fate of primary intestinal tuberculosis in terms of spread?

It only spreads lymphatically

It doesn't spread at all

It only spreads hematogenously

It can spread both directly and lymphatically, as well as hematogenously (correct)

What is the most common complication of tuberculous ulcers?

Fibrosis leading to intestinal obstruction Signup and view all the answers

What is the aetiology of secondary intestinal tuberculosis?

Swallowing infected sputum in patients with chronic fibrocaseous tuberculosis Signup and view all the answers

What is the characteristic arrangement of tuberculous ulcers in the terminal ileum?

Transverse Signup and view all the answers

What is the pathology of primary intestinal complex?

Intestinal lesions, tuberculous lymphangitis, and tuberculous lymphadenitis Signup and view all the answers

What is the consequence of fibrosis in intestinal tuberculosis?

Intestinal obstruction Signup and view all the answers

What is a rare complication of intestinal tuberculosis?

Secondary amyloidosis Signup and view all the answers

What is the characteristic feature of caseous necrosis in intestinal tuberculosis?

It is soft and yellowish Signup and view all the answers

Study Notes

Granuloma (TB)

Tuberculosis is a chronic infective granuloma caused by Mycobacterium tuberculosis, also known as tubercle bacilli (human and bovine).
Mycobacterium tuberculosis is a non-motile, acid-fast, and alcohol-fast organism that is very resistant but easily killed by sunlight.
The pathological changes depend on the chemical structure of the bacteria, which consists of three components: a lipid fraction (capsule), a protein fraction (tuberculoprotein), and a small polysaccharide fraction.

Predisposing Factors

Poverty
Malnourishment
Poor living conditions
Lack of medical care or debilitating/immunosuppressive conditions

Route of Infection

Inhalation (commonest method)
Ingestion of raw milk contaminated with bovine or human bacilli, infecting the tonsils or intestine
Skin inoculation by handling infected materials (rare)

Tubercle Formation

Type IV hypersensitivity reaction
Polysaccharide fraction of tubercle bacilli attracts neutrophil leucocytes within a few hours
Lipid fraction of the capsule attracts macrophages, which phagocytose free bacilli (epitheloid cells)
Bacilli are partially digested, releasing tuberculoprotein, which stimulates a cell-mediated immune response within 10 days

Macroscopic Picture

Tubercles fuse to form small rounded gray follicles (1-2 mm in diameter)
Caseation occurs, making the lesion appear pale yellow and cheesy in consistency

Pathogenesis

Proliferative reaction (inflammatory cells)
Exudative reaction (excess inflammatory fluid exudate)

Fate of Tubercle

High immunity: small foci are completely fibrosed, large foci are capsulated by fibrous tissue with central caseating part showing dystrophic calcification
Low immunity: direct spread, lymphatic spread, blood spread, or intracanalicular spread

Pulmonary Tuberculosis

Primary pulmonary tuberculosis: first infection of the lung with tubercle bacilli, often in children, caused by inhalation of human bacilli
Secondary pulmonary tuberculosis: tuberculous infection in a previously sensitized individual with lowered immunity

Primary Pulmonary Complex

Triad of:
- Ghon's focus (yellowish lesion, 1-1.5 mm in diameter, commonly subpleural)
- Tuberculous lymphangitis (chain of tubercles along lymphatic vessels)
- Tuberculous lymphadenitis (enlarged hilar lymph nodes with caseating tubercles)

Fate of Primary Pulmonary Complex

Healing: small lesion heals by complete fibrosis, bigger one heals by dystrophic calcification
Spread: direct spread (tuberculous pneumonia, pleurisy), haematogenous spread (small number of bacilli: destroyed, moderate number: isolated organ tuberculosis, large number: miliary tuberculosis), or encapsulation and reactivation

Secondary Pulmonary Tuberculosis

Infection: exogenous (inhalation of human bacilli) or endogenous (reactivation of a capsulated primary focus)
Pathological features: start at the apex of the lung, commonly the right
Course: regression (fibrotic tuberculosis), progression (chronic fibrocaseous pulmonary tuberculosis or acute fatal bronchopneumonia and acute caseous pneumonia)

Intestinal Tuberculosis

Primary intestinal tuberculosis: due to ingestion of bovine bacilli in milk, forming a primary complex usually at the terminal ileum
Secondary intestinal tuberculosis: due to swallowing infected sputum in patients with chronic fibrocaseous tuberculosis

Primary Intestinal Complex

Intestinal lesions: tubercles in the Peyer's patches at the terminal ileum (minimal ulcers)
Tuberculous lymphangitis and lymphadenitis (tabes mesentaris)