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Questions and Answers
In the context of tuberculous granuloma formation, what specific mechanism prevents the complete eradication of Mycobacterium tuberculosis within macrophages, leading to chronic infection?
In the context of tuberculous granuloma formation, what specific mechanism prevents the complete eradication of Mycobacterium tuberculosis within macrophages, leading to chronic infection?
- Interference with phagosome-lysosome fusion, leading to intracellular bacterial survival due to the absence of lysosomal enzymes. (correct)
- Downregulation of NADPH oxidase assembly, impairing reactive oxygen species (ROS) production and subsequent bacterial killing.
- Upregulation of autophagy, promoting bacterial degradation within autophagosomes, thereby reducing the antigen load presented to T cells.
- Enhanced presentation of mycobacterial antigens via MHC class II molecules, resulting in effective activation of cytotoxic T lymphocytes (CTLs) and bacterial clearance.
What is the most accurate description of the pathogenesis of secondary tuberculosis in relation to the host's immune response?
What is the most accurate description of the pathogenesis of secondary tuberculosis in relation to the host's immune response?
- A robust Th1 response, characterized by an intense local inflammatory reaction and heightened cell-mediated immunity, is triggered, leading to increased tissue destruction and cavitation. (correct)
- A dominant Th17 response exacerbates neutrophil recruitment and extracellular trap (NET) formation, effectively containing the infection with minimal tissue damage.
- A weakened Th1 response leads to uncontrolled bacterial replication, resulting in widespread dissemination and reduced tissue damage.
- An inadequate Th2 response fails to stimulate sufficient antibody production, preventing the opsonization and clearance of _Mycobacterium tuberculosis_.
Which of the following statements best elucidates the role of caseous necrosis in the context of tuberculous granulomas?
Which of the following statements best elucidates the role of caseous necrosis in the context of tuberculous granulomas?
- It is a form of liquefactive necrosis, characterized by enzymatic digestion of necrotic cells, leading to the formation of a fluid-filled cavity.
- It is a manifestation of coagulative necrosis, resulting from ischemia and subsequent denaturation of cellular proteins within the granuloma.
- It is a distinct form of necrosis characterized by the preservation of the tissue architecture and the absence of inflammatory cell infiltration.
- It represents a unique type of cell death that combines features of both necrosis and apoptosis, resulting in the formation of a cheese-like substance. (correct)
How does the immune response in primary tuberculosis differ fundamentally from that in secondary tuberculosis in terms of granuloma formation and disease progression?
How does the immune response in primary tuberculosis differ fundamentally from that in secondary tuberculosis in terms of granuloma formation and disease progression?
A patient presents with a large, solitary lung lesion, suspected to be either a tuberculoma or a malignant neoplasm. What advanced diagnostic approach, beyond standard histopathology, would best differentiate between these two entities with high certainty?
A patient presents with a large, solitary lung lesion, suspected to be either a tuberculoma or a malignant neoplasm. What advanced diagnostic approach, beyond standard histopathology, would best differentiate between these two entities with high certainty?
Flashcards
Tuberculosis (Definition)
Tuberculosis (Definition)
Chronic infective granuloma affecting nearly all body systems, mainly the lungs, caused by TB bacilli.
Tuberculosis Mode of Infection
Tuberculosis Mode of Infection
By droplet infection from an open, active pulmonary disease, or by drinking raw contaminated milk (Bovine type).
Tubercle Characteristics
Tubercle Characteristics
Small (1-3 mm) with central yellow caseation and grey periphery, structureless eosinophilic material, epithelioid cells, macrophages, Langhan's giant cells, lymphocytes.
Miliary TB Lung
Miliary TB Lung
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Hydatid Disease
Hydatid Disease
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Study Notes
- Pathology of tuberculosis and hydatid cysts are examples of granulomas
- Tuberculosis is a chronic infective granuloma
- It affects nearly all body systems, mainly the lungs
- It is caused by TB bacilli
- TB is the leading cause of death worldwide after HIV
Predisposing Factors
- Environmental factors include low socioeconomic standard, bad general hygiene, contact with tuberculous persons, overcrowding, and environmental pollution
- Personal factors include being of African descent, malnutrition, debilitating diseases such as diabetes mellitus, and immune deficiency states
T.B. Bacilli
- Are aerobic, acid-fast and non-motile
- Does not produce toxins and is carried by macrophages
- The structure is carbohydrate, lipid, and protein, specifically tuberculoprotein
- Types include Human, Bovine, and others/atypical
Mode of Infection
- Human type spreads via droplet infection from an open, active pulmonary disease
- Bovine type spreads through oropharyngeal and intestinal lesions, acquired by drinking raw, contaminated milk
Primary Tuberculosis
- Typically occurs in young, non-immunized persons
- Methods of infection include inhalation, ingestion, and direct contact
- Sites of primary complex include lung, intestine, tonsils, skin, and rarely the nose
- Tubercle appearance is small, 1-3 mm, with central yellow caseation and a gray periphery
- Has central caseating material (structureless eosinophilic material), epithelioid cells, macrophages, Langhan's giant cells, lymphocytes, and peripheral fibroblastic reaction
Primary Complex Constituents
- Parenchymatous lesion (Ghon's focus)
- Tuberculous lymphangitis
- Tuberculous lymphadenitis
Fate of Primary Complex
- Good outcomes include healing with a small fibrous scar, calcification, and encapsulation if large, with the organism potentially dying or remaining dormant
- Bad outcomes include local, lymphatic, and hematogenous spread which is more common than in secondary tuberculosis, and less common natural passage spread than in secondary tuberculosis
Secondary Tuberculosis
- Typically occurs in adulthood
- Methods of infection include endogenous reactivation of a dormant focus and exogenous inhalation or ingestion
- Can affect any site, mainly the lung and intestine
Reaction of Body Against Bacilli in Secondary Infection
- Hypersensitivity reaction leads to excessive tissue destruction and extensive caseation
- There is no nodal affection because the organism is destroyed in the necrotic tissue
- Commonly affected organs include the kidney, suprarenal gland, fallopian tube, epididymis, brain, meninges, bones, and joints
Secondary Pulmonary Tuberculosis
- Begins as an apical lesion (Assmann focus), a small caseating tuberculous granuloma
- Destruction of the lung often leads to cavitations
Secondary Pulmonary Tuberculosis M/E
- A central area of caseation is surrounded by granulomatous inflammatory reaction
Fate of Secondary T.B.
- Good fate includes healing
- Bad fate includes Extension and spread which can be local, through natural passages (more than primary TB), blood (rarer than primary TB), or lymphatic routes
Primary TB vs. Secondary TB
| Primary TB | Secondary TB | |
|---|---|---|
| Mode of infection | Exogenous | Endogenous or exogenous |
| Age | Childhood | Adults |
| Sites | Affects only organs exposed to exogenous infection | Affects any organ |
| Gross lesions | Primary complex, no cavity or ulcer | Fibrocaseous, cavity, ulcers, More extensive caseation |
| Proliferative reaction | Slowly occurring, less extensive, less caseation | extensive, exaggerated, rapid to occur, with more caseation, the caseation material is more in amount, soft and can be liquefied |
| Spread | lymphatic & blood spread. Can occur. Rare spread by natural passages | Spread by natural passages can occur, rare lymphatic or blood spread |
Tuberculoma
- Is a localized mass of caseating tuberculous reaction surrounded by fibrous tissue
- Can reach a large size, possibly mistaken for a tumor
- Can occur in any organ, including the lung, kidney, brain, and spinal cord
Miliary TB Lung
- Results from acute hematogenous dissemination of a large dose of T.B. bacilli, leading to widespread involvement of multiple organs
- Affected organs show a large number of small, uniform, grayish-yellow dots near small blood vessels without surrounding hyperemia
- Patterned like millet seeds
Miliary TB M/E
- The affected organ displays numerous small, uniform epithelioid granulomas with giant cells, but minimal caseation & little to no surrounding fibrosis
Complications of Secondary Tuberculosis
- Hemorrhage
- Obstruction of tubular organs due to adhesion
- Spread to peritoneum and serous coverings
- Rare perforations due to fibrosis and adhesion
- Amyloidosis
Hydatid Disease
- Is an infective parasitic disease transmitted from animals (dogs) to humans
- It is caused by ingestion of eggs of Echinococcus granulosus
- These eggs contaminate food, hatch in the intestine, and travel with portal blood to the liver, where they mature into the larval stage (hydatid cyst)
- May pass to the systemic circulation, reaching different organs
Pathology of Hydatid Cyst
- Can reach 20 cm in diameter
- The lumen contains straw-colored fluid
- The inner germinal layer forms scolices
- There is an outer chitinous laminated layer and a surrounding fibrous capsule
Complications of Hydatid Cysts
- Allergic manifestations with anaphylactic shock
- Abscess formation due to secondary bacterial infection of the cyst
- Pressure atrophy on surrounding tissue
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