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Tuberculosis (TB)

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 23 September 2011, last major update September 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.


● Due to Mycobacteria tuberculosis
● In developing world, M. bovis causes oropharyngeal and intestinal TB
● Very prevalent, approximately 1.7 billion people are infected with 9 million new cases a year with an estimated 1.6 million deaths
● In the United States, there are 11,000 new cases of active TB each year
● Transmission is from person to person via airborn droplets, infections may be dormant for years
● Infection does not mean disease; most infected individuals are asyptomatic; the genetic makeup of the host affects disease severity
● TB is often a disease of poverty, overcrowding and associated with other chronic diseases
M. tuberculosis primarily infects macrophages
● Lung involvement is the major cause of morbidity/mortality
● Multidrug-resistant TB and extensive drug-resistant TB have recently emerged as clinical and public health challenges that have come about, at least in part from incomplete compliance with drug treatment regiments
● Cases increasing due to AIDS and emergence of multi-drug resistant strains; AIDS patients may lack granulomas
● AIDS patients are more susceptible to TB and have more severe disease
● There is also increased risk with alcoholism, immunosuppression (immunotherapy with TNF antagonists, lymphoma, especially Hodgkin lymphoma), chronic renal disease and chronic lung disease
● Rarely involves skin, oropharynx and lymphoid tissue
● Initial focus of infection is Ghon complex, consisting of parenchymal subpleural lesion, near upper/lower lobe interlobar fissure (apex has high oxygen tension) with enlarged caseous lymph nodes
● Lesions usually undergo fibrosis, calcification and cause no symptoms
● Rarely (infants, children, immunocompromised), get progressive spread with cavitation, TB pneumonia and miliary TB
Screening: in much of the developed world Interferon-Gamma release assays have supplanted Mantoux Tuberculin skin testing


● Prolonged multi-agent antibiotics
● Lung resection indicated for: open cavity after 4-6 months of drug therapy, residual caseous disease, irreversible destructive lesion (bronchiectasis, bronchial stenosis), recurrent hemorrhage, unexpandable lobe with associated TB empyema, suspected tumor; surgical success rate (inactive disease) is 80% after 2-5 years

Gross description

● Inflamed, fibrotic, non-functioning lung parenchyma
● May have bronchial strictures, bronchiectasis, cavitation and thickened pleura

Gross images

Multiple granulomas

Granulomas with caseous necrosis


Ghon complex


Miliary TB

Micro description

● Caseating granulomas
● Cavities show approximation of walls, granulation tissue, fibrosis and stellate scar
● May have metaplastic bone formation

Micro images

Caseating granuloma

Virtual slides


Caseating granuloma

Secondary (reactivation) pulmonary TB


● 5-10% of cases of primary infection
● Produces more damage than primary TB
● Apical areas of consolidation with caseous necrosis in draining nodes
● Usually get progressive fibrous encapsulation, which causes focal pleural adhesions; may contain anthracotic pigment
● Tubercles coalesce over time, creating confluent area of consolidation
Diagnosis: appearance of bacteria with acid-fast stain, positive smears or cultures; 1 bacillus in a 1 cm3 granuloma indicates the presence of 2000 organisms

Micro description

● Caseating granulomas with Langhans giant cells

Progressive pulmonary TB


● Progression to cavitary disease, miliary TB or TB bronchopneumonia
Cavitary disease: drainage of caseous focus transforms it into a cavity, usually in apex and walled off; may spread to other parts of lung, producing endobronchial and endotracheal TB, laryngeal seeding and intestinal TB
Miliary TB: seeds bone marrow, liver, spleen, retina via blood or lymphatics; grossly see distinct, small, yellow-white areas of consolidation, central necrosis identifiable microscopically
TB bronchopneumonia: occurs in highly sensitized, highly susceptible people; also called “galloping consumption”; multi-agent treatment is effective unless resistant organisms, diabetes, AIDS and reactive amyloidosis



● Due to reinfection; may rupture and cause widespread dissemination


● Excision to rule out malignancy and destroy possible nidus for infectious spread

Gross description

● Round, discrete, solitary, firm nodules, adjacent to pleura
● May have concentric laminations, cavitation or calcification
● May communicate with bronchus

Micro description

● Persistent caseation surrounded by thick fibrous walls with Langhans giant cells, epithelioid histiocytes and lymphocytes
● Also subpleural fibrous thickening

Positive stains

● Acid-fast bacilli

End of Lung-nontumor > Infections > Tuberculosis (TB)

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