TB pathology

Question 1

what happens in Primary Pulmonary TB

Answer 1

Develops in a previously unexposed /unsensitised host (ie. first contact with bacillus)
Usually implant in upper lobes

1 – 1.5 cm area of consolidation develops - Ghon focus (inflammation, granulomas and caseous necrosis)

Tubercle bacilli drain into local lymph nodes » Ghon complex.

95% of cases cell mediated immunity controls the infection

Most cases heal by scar formation and eventual calcification

Clinically
Usually asymptomatic
Rarely – fever, pleural effusions

Question 2

Ghon complex:

Answer 2

Ghon complex:
Yellow, necrotic areas in parenchyma & nodes

1 – 1.5 cm area of consolidation develops - Ghon focus (inflammation, granulomas and caseous necrosis)

Question 3

what happens in Secondary Pulmonary TB

Answer 3

Form of disease that arises in a previously sensitised host.

May follow shortly after 1º TB
Usually arises from reactivation of dormant 1º lesions
May also result from re-infection

Classically localised to apices of the upper lobes due to high oxygen tension
Pre-existing hypersensitivity » marked tissue response “walling off” infective focus » high risk of cavitation

Clinically:
Asymptomatic
Insidious manifestations (related to cytokine release by activated macrophages)

Question 4

what happens in Cavitating TB

Answer 4

Apical lesion enlarges

Expansion of area of caseation creating a ragged cavity

Clinically:
Erosion of vessels »haemoptysis
Drainage into bronchus/bronchiole » cough / increased amounts of sputum
Fever etc

Adequate tx:
Heal by fibrosis

Inadequate tx +/- debilitation
Dissemination via airways, lymphatics or vascular channels
Spread into upper airways & gut - open TB

Question 5

what happens in Miliary Pulmonary TB

Answer 5

Haematogenous spread – organisms drain into lymphatics » venous system » right side of heart » pulmonary arteries ….

Scattered small foci (< 2 mm) of consolidation
Foci of consolidation may expand and coalesce

Question 6

what happens in Tuberculous Bronchopneumonia

Answer 6

Rapid spread via airways (open TB)
Extensive parenchymal inflammation
Rare with tx but prognosis poor

Question 7

what happens in Systemic Miliary TB

Answer 7

Infective foci in lungs enter the systemic circulation

Liver, spleen, bone marrow, adrenals, meninges, kidneys, fallopian tubes and epididymis common

Prognosis poor despite treatment

Question 8

what is Isolated Organ TB:

Answer 8

Isolated Organ TB:

Single episode of haematogenous spread
Bone, kidney, adrenals, meninges, genital tract
Within the spine: “Pott’s” disease

Prognosis good with tx

Question 9

what happens in Mycobacterium Avium/Intracellulare Complex

Answer 9

MA and MI are different species

Atypical mycobacterium
Opportunistic infection
Uncommon except in AIDS with low CD4 lymphocytes
Organisms proliferate in lungs and GI tract
Clinically
Fever, drenching sweats and weight loss

Abundant acid-fast bacilli within macrophages

Granulomas and necrosis rare in immunodeficient patients