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Pathology > tuberculosi > Flashcards

tuberculosi Flashcards

1
Q

What is tuberculosis?

A
  • infective granuloma (cronic specific inflammation) caused by mycobacterium tuberculosis (tubercle bacilli)
  • bacteria neither produce exotoxins or liberate endotoxins
  • all pathological lesion are caused by hypersensitivity reactions
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2
Q

What is the structure of the bacteria that causes tuberculosis?

A

the bacilli have three components, namely polysaccharide fraction, lipid fraction and tuberculoprotein

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3
Q

What are the methods of infetion of tuberculosis?

A
  • inhalation: goes to lungs or tonsils, infection comes from patient (droplet infection) or inhalation of dust contaminated with bacteria
  • ingestion: goes to intestine or tonsils, infection comes from ingestion of infected milk
  • skin contact: rare.
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4
Q

What are the tissue reactions in tuberculosis?

A

there are two types of tissue reactions: namely proliferative or primary and exudative or secondary depending upon whether it is the first or second contact between th bacilli and the human tissues

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5
Q

What is proliferative tissue reaction?

A
  • represents the first contact between the tubercle bacilli and the human tissues
  • it is characterized by nodular collection of chronic inflammatory cells, especially macrophages with the formation of small tubercles
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6
Q

What are the steps of tubercle formation?

A
  1. the polysaccharide fraction attracts polymorphs within few hours, they come engulf the bacteria and die because they cannot digest the lipid capsule (no lipase enzyme)
  2. the macrophages (blood monocytes and tissue histiocytes) are attracted by the lipid fraction after the first day, they engulf the bacilli, digest the lipid fraction and change into epithelioid cells
  3. some tuberculo-protein is released which stimulates cell-mediated immune response within 10 days, the sensitized T-lymphocytes come, surround the epithelioid cells and release lymphokines which:
    - attract more macrophages
    - inhibit macrophage migration from site of inflammation
    - transfere sensitization to other lymphocytes
    - cause tissue necrosis [caseous necrosis = caseation]
    - cause positive skin test (tuberculin test)
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7
Q

What is the gross picture of tubercle?

A

multiple fused tubercles appear as small gray focus with yellow cheesy center

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8
Q

What is the microscopic picture of tubercle?

A

rounded or oval collection of epithelioid cells, lymphocytes and Langhan’s giant cells

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9
Q

What are epithelioid cells?

A

pale cells with pale cytoplasm, pale nucleus and pale borders (epithelial like)

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10
Q

What are langerhan’s giant cells?

A

large cells with multiple nuclei arranged at the periphery in the form of a horse-shoe shape. They engulf caseous material and bacteria

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11
Q

What do lymphocytes do during primary tissue reaction?

A
  • form a ring around epithelioid cells and extend between them
  • with the development of hypersensitivity, caseation starts in the center then it may involve the whole tubercle
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12
Q

What is the fate of tubercle?

A
  • with high immunity: small lesion –> fibrosis - large lesion –> encapsulation and dystrophic calcification, the bacteria may remain alive for many years and may become active again
  • with low immunity: spread by all methods –> direct, lymphatic, blood, etc….
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13
Q

What is exudative tissue reaction?

A

represents the second contact between the tubercle bacilli and the human tissues whether due to re-infection or re-activation

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14
Q

What is exudative tissue reaction characterised by?

A
  • rapid formation of tubercles
  • rapid caseation of tubercles
  • rapid liquefaction of caseous material
  • rapid evacuation of liquefied caseous material (formation of ulcer or cavity)
  • rich exudate in fluids, fibrin, neutrophils and lymphocytes (to convert from solid to liquid)
  • no spread to lymph vessels or lymph nodes (but can cause fatal loss of organs)
  • best seen in serous membranes [Pleura, Pericardium & Peritoneum]
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15
Q

Is the rapid evacuation of liquefied caseous material always good?

A
  • it doesn’t have to b a positive thing
  • can cause Tb in the vocal cords, tonsils or intestine
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16
Q

What is the spread of tuberculosis infection?

A
  • direct spread: macrophages and tissue fluid carry bacilli to surroundings
  • lymphatic Spread: macrophages and lymph carry bacilli to lymph vessels causing lymphangitis and lymph nodes causing lymphadenitis
  • blood spread: the effect will depend upon the number of bacilli:
  • small numbers –> destroyed by RE cells –> no effect
  • moderate numbers –> settle in one organ –> isolated organ T.B.
  • large numbers –> settle in many organs –> miliary T.B.
  • intra-canalicular spread: through lumen of a natural tube, e.g. ureter
17
Q

What is primary pulmonary tuberculosis?

A
  • represents the first contact between the lung and the tubercle bacilli
  • usually follows inhalation of human type in dust or droplets
  • seen in children and is called childhood type
  • characterized by three lesions (traid of lesions), namely:
  • lesion in the lung = ghon’s focus: located usually in the right lung, under the pleura at the lower part of upper lobe, it appears as a small area of caseation that heals by fibrosis and calcification (smallest leson)
  • tuberculous lymphangitis: the draining lymph vessels whow multiple tubercles and appear beaded (medium sized)
  • tuberculous lymphadenitis: the hilar lymph nodes are enlarged, matted, fixed, soft and caseous (the lesion in the lymph nodes is much larger than the ghon’s focus)
  • the three lesions are called primary pulmonary complex.
18
Q

What is the fate of primary pulmonary complex?

A
  • with high immunity: healing occurs
  • with low immunity: spread by all methods
19
Q

What is secondary pulmonary tuberculosis?

A
  • represents the 2nd contact between the lung and the tubercle bacilli
  • may follow inhalation of human type of bacilli (re-infection) or reactivation of an old encpauslated primary focus
  • the picture will depend on three factors namely: the dose of the bacilli, the state of immunity and the state of hypersensitivity
20
Q

What are the variants that might be seen fo secondary pulmonary tuberculosis?

A
  • fibrotic lesion
  • chronic fibro-caseous tuberculosis
  • tuberculous pneumonia
  • miliary tuberculosis
21
Q

What is tuberculous lymphadenitis?

A
  • almost always primary in origin, i.e. it is part of the primary complex in the lungs, tonsils or intestine
  • although primary in origin, but it is secondary in nature, this is becuase by the time by which the bailli reach the lymph nodes, they become sensitized and react with hypersensitivity
  • groups affected are: the hilar [in 1ry pulmonary], cervical [in 1ry tonsillar] and mesenteric [in 1ry mesenteric] lymph nodes.
  • affected lymph nodes appear: enlarged, matted, fixed, soft and caseous
  • micro: the lymph node shows at first multiple tubercles formed of epithelioid cells, langerhan’s giant cells and lymphocyteswith minimal or no caseation, but later on, caseation becomes extensive and the whole lymph node may change into pink homogenous caseous material
22
Q

What are the complications of tuberculous lymphadenitis?

A
  • if it opens to surface (cervical): the caseous material is evacuated and leaves a tuberculous sinus
  • if it does not open to the surface (chest and intestine): it results in cold abscess formation [localized collection of liquified caseous material]
    Spread of infection: direct, lymphatic or blood
23
Q

What happens in cold abscesses?

A
  • rapid formation
  • rapid caseation
  • rapid liquefaction
  • rapid collection of liquefied caseous material
24
Q

What is tuberculosis of vertebrae (pott’s disease)?

A
  • tuberculous osteomyelitis of the vertebrae
  • always secondary (fast) in origin, i.e. the bacilli reach the vertebrae via the blood stream
  • vertebrae commonly affected are the lumbar (lower), cervical (at neck) and thoracic (at chest)
  • vertebral bodies and intervertebral discs are destroyed.
25
Q

Does TB occur to sacral vertebrae?

A

no, because it is not moving

26
Q

What organs does TB occur as primary TB?

A
  • tonsil
  • lung
  • intestine
27
Q

Why does TB destroy vertebral bodies?

A
  • they have many blood vessels
  • TB enters in spine
  • affects motor nerve
  • paralysis
28
Q

What is Pott’s disease characterised by?

A
  • kyphosis: due to anterior collapse of vertebral bodies
  • cold abscess: due to collection of liquified caseous material
  • paraplegia (in lumbar TB) or quadriplegia (in cervical TB): due to compression of spinal cord by oedema, cold abscess or obliterated arteries

Pathology (5 decks)

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