Tuberculosis Granulomas

• Chronic specific inflammation includes the pathology of tuberculosis and hydatid cysts as examples of granulomas.
• Tuberculosis, hydatid cyst as an example of Granulomas by Dr. Mie Ali Mohamed, Professor of Pathology at Mansoura University.

Tuberculosis

• Tuberculosis is a chronic infective granuloma
• Tuberculosis affects nearly all body systems, mainly the lungs
• Tuberculosis is caused by TB bacilli
• TB is the leading cause of death worldwide after HIV.

Predisposing Factors to Tuberculosis

• Environmental factors include low socioeconomic standards, bad general hygiene, contact with tuberculous persons, overcrowding, and environmental pollution
• Personal factors include race (more common in Negroes), malnutrition, debilitating diseases (e.g., diabetes mellitus), and immune deficiency states

Characteristics of T.B. Bacilli

• Aerobic
• Acid-fast
• Non-motile
• Do not produce toxins
• Carried by macrophages
• Structure: Carbohydrate, lipid, and protein (tuberculoprotein)
• Types: Human, bovine, and others

Mode of Infection

• Human type: Droplet infection from an open, active pulmonary disease
• Bovine type: Acquired through oropharyngeal and intestinal lesions by drinking raw contaminated milk containing bacilli

Types of Tuberculous Reaction

• Primary tuberculosis results from no prior exposure
• Secondary tuberculosis results from prior exposure through Type IV Hypersensitivity Response

Pathogenesis of Tuberculosis

• Primary Pulmonary Tuberculosis is a reaction that occurs around weeks 0-3
• The antigen presenting cell presents to the Helper T cell
• CD4+ TH1 cell contains Antigen, IL-12
• Giant Cell and Epithelioid Cell are also part of the lymphocyte
• Alveolar macrophages undergo endosomal manipulation, maturation arrest as well as ineffective phagolysosome formation

Primary Tuberculosis (Childhood Type)

• Occurs in young, non-immunized persons
• Methods of infections: Inhalation, ingestion, and direct contact
• Sites of primary complex: lung, intestine, tonsils, skin, and nose (rare)
• N/E (Naked Eye) of tubercle: Small, 1-3 mm, with central yellow caseation and grey periphery
• M/E (Microscopic Eye) of tubercle: Central caseating material (structureless eosinophilic material), epithelioid cells, macrophages, Langhan's giant cells, lymphocytes and peripheral fibroblastic reaction
• The reaction ends by the formation of epithelioid granulomas with giant cells and peripheral fibrosis

Primary Complex Constituents:

• Parenchymatous lesion (Ghon's focus)
• Tuberculous lymphangitis
• Tuberculous lymphadenitis

Fate of the Primary Complex:

• Good fate: Healing with a small fibrous scar, calcification & encapsulation if large. The organism may die or remain dormant in the healed lesion
• Bad fate: Spread either locally, lymphatically, hematogenously (more than in secondary tuberculosis), or through natural passages (less than in secondary tuberculosis)

Secondary Tuberculosis (Adulthood Type)

• Methods of infection: Endogenous reactivation of dormant focus or exogenous inhalation/ingestion
• Sites: Any site, mainly the lung & intestine

Secondary Infection Reaction

• Reaction of the body: Hypersensitivity reaction leads to tissue destruction and extensive caseation
• Nodal affection: There is No nodal affection as the organism is destroyed in the necrotic tissue
• Organs affected include the kidney, suprarenal gland, fallopian tube, epididymis, plus the brain, meninges, bone, and joints.

Secondary Pulmonary Tuberculosis

• An apical lesion, known as Assmann focus, begins as a small caseating tuberculous granuloma
• It leads in most cases to destruction of the lung leading to cavitations
• There's a central area of caseation that is surrounded by granulomatous inflammatory reaction

Fate of Secondary T.B:

• Good fate: Healing
• Bad fate: Extension and spread locally, or through natural passages (more than 1ry TB), blood (rare than 1ry TB, or lymphatic

Primary TB vs Secondary TB

• Mode of infection: Primary is exogenous, secondary is endogenous or exogenous
• Age: Primary occurs in childhood, secondary occurs in adulthood
• Sites: Primary affects only organs exposed to exogenous infections, while secondary can affect any organ
• Gross lesions: Primary complex with no cavity or ulcer, while secondary has fibrocaseous, cavity, ulcers and more extensive caseation
• Criteria of proliferative reaction: Primary is slowly occurring with less extensive area and less caseation, while secondary is extensive, exaggerated, and rapid with more caseation. Caseation material is more in amount, soft and can be liquefied
• Spread of infection: In primary it spreads through, lymphatic & blood; rare by natural passages, in secondary TB it spreads through natural passages more readily; rare, lymphatic or blood spread

Tuberculoma

• It is a localized mass of caseating tuberculous reaction surrounded by fibrous tissue
• It may reach a large size and be mistaken for a tumor
• Can occur in any organ such as lungs kidneys brain spinal cord

Miliary TB Lung

• Definition: Acute hematogenous dissemination of a large dose of Tuberculosis bacilli with widespread involvement of multiple organs

Miliary TB Lung (Grossly):

• The affected organ shows a large number of small, uniform, grayish-yellow dots
• Located near small blood vessels
• No surrounding zone of hyperemia
• The millet seeds for which the pattern is named, have a similar size

Miliary TB

• The affected organ shows a large number of small, uniform epithelioid granulomas with giant cells
• There is little caseation and little or no surrounding fibrosis

Complications of Secondary Tuberculosis

• Hemorrhage
• Obstruction if tubular organ (due to adhesion)
• Spread to peritoneum and serous coverings
• Perforations are rare (due to fibrosis and adhesion)
• Amyloidosis

Hydatid Disease

• Definition: An infective parasitic disease transmitted from animal (dog) to man
• Pathogenesis: Caused by ingestion of the eggs of Ecchinococcus granulosus
• The eggs contaminate food, hatch in the intestine, and pass with portal blood to the liver, where they mature into a larval stage (hydatid cyst)
• It may pass to the systemic circulation, reaching different organs

Pathology of Hydatid Cysts:

• Hydatid cysts may reach 20 cm in diameter.
• It is composed of:
  • A lumen containing straw-colored fluid
  • An inner germinal layer that forms scolices
  • An outer chitinous laminated layer
  • A surrounding fibrous capsule

Complications of Hydatid Cysts:

• Allergic manifestations with anaphylactic shock
• Abscess formation owing to secondary bacterial infection of the cyst
• Pressure atrophy on the surrounding tissue