Tuberculosis

TUBERCULOSIS
• It is also known as Koch’s disease.
• They are acid fast due to presence of mycolic acid.
• Virulence factor is “cord factor”
Two types
a) Primary tuberculosis
• Most commonly seen in children
• It is seen in unsensitised and unexposed individuals
• Source of organism is exogenous.
• Most common site is lung.
• most commonly starts as “latent disease”.
• Unilateral hilar lymph enlargement is seen.
• Calcification, Pleural effusion, Erythema nodosum and Phlyctenular conjunctivitis are also seen.

• Some named Lesions are :
1) Ghon’s focus:- 
Subpleural fibrocaseous lesion (consolidation) of lung parenchyma
Most commonly seen at lower part of upper lobe
Microscopically contains epithelioid granulomatous inflammation
2) Ghon’s complex:-
Consists of Subpleural Ghon’s focus and involved lymph nodes.
Ghon's complex found below clavicle.
3) Ranke’s complex :
Ghon’s focus along with fibrosis and calcification.
4) Simon focus 
It is a tuberculous (TB) nodule formed in lung apex. 
Due to spread of primary TB infection from elsewhere in the body to lung apex via bloodstream. 

b) Post-primary (=Secondary) Pulmonary tuberculosis
• Seen in previously sensitized host due to reactivation of latent primary lesions.
• Frequently associated with decreased immune status.
• Pulmonary fibrosis and cavitation are common.
• Lymph node involvement is rare.
• Endobronchial spread along nearby airways is relatively common finding, resulting in relatively well-defined 2-4 mm nodules or branching lesions “tree-in-bud appearance” on CT.
• Tuberculomas and miliary TB are also recognized patterns of secondary TB.
• Lesions seen are 
1) Puhl’s lesion:-
• Lesion in lung apex and supraclavicular.
• No lymph node involvement.
2) Assman focus:
• Infraclavicular lesion of chronic pulmonary T.B.
Miliary pulmonary tuberculosis
• It is uncommon but carries a poor prognosis.
• It represents hematogenous dissemination of an uncontrolled tuberculous infection.
• Most commonly seen post-primary tuberculosis. 
• Miliary deposits appear as 1-3 mm diameter nodules.
• Lesions are
a) Rich focus 
• It is a tuberculous granuloma occurring on brain cortex.
b) Weigert’s focus :
• Subintimal foci in pulmonary vein.
c) Simond’s focus:
• Localized foci in liver.

Congenital tuberculosis
• Infection with tubercle bacilli either during intrauterine life or before complete passage through birth canal is termed as congenital tuberculosis.
• Three possible modes of infection of fetus
1) Hematogenous infection via umbilical vein
2) fetal aspiration of infected amniotic fluid 
3) fetal ingestion of infected amniotic fluid
• Most common site (overall) and most common site for “primary complex” for “congenital Tuberculosis” is Liver.

• Revised criteria for diagnosis of congenital tuberculosis ( by Cantwell ):
Proven tuberculosis lesions in the infant plus one of the following:
1) Lesions occurring in the first week of life
2) A primary hepatic complex
3) Maternal genital tract or placental tuberculosis
4) Exclusion of postnatal transmission by thorough investigation of contacts.