Most common site of primary tuberculosis is (LQ)
Ref. Robbins,8th ed., page 370
1). Usually occurs in childhood, and the lungs are the most frequent site of initial contact with the tubercle bacilli. Transmission of TB is via inhalation.
2). Primary Focus: (also known as Gohn focus)
a. Almost always found just beneath the pleura in the basal segment of the upper lobe or apical segment of lower lobe. (where there is greatest volume of inspired air.)
b. The focus is usually small (<1cm). Microscopically, typical caseating granulomas are seen.
c. Organisms drain to hilar nodes, again with formation of granulomas.
3). Primary (Ghon) Complex = Primary focus + involvement of regional lymph nodes in primary TB.
4). Primary foci are usually entirely asymptomatic.
5). The old sites of the healed primary TB infection may be marked by a pulmonary nodule or granuloma in the lung, which over time may become calcified. These nodules are known as "Ghon lesions"
6). When seen together with ipsilateral calcified hilar adenopathy, the finding is termed a “Ranke’s complex”.
7). Apical scarring with the appearance of a fibronodular patch or ill-defined reticular shadow in the upper lung fields on chest x-ray is known as "Simon's focus" and in a patient with a positive tuberculin skin test identifies a patient with a markedly increased risk for active TB.
8). Purl's Lesion - Lesion at the apex of lung in chronic TB - commonest site of isolated lesion in chronic TB
9). Assmann’s Focus - Typically apical (site of highest oxygen tension)
10). Simon's Focus - Early hematogenous seedling in apex of lungs
11). Rich Focus - tuberculous caseous foci in brain, meninges and spinal cord
a. In young children with a positive tuberculin test extensive physical changes were found in the chest, consisting of an impaired. Percussion note with diminished or tubular breathing, mostly localized in the upper lobe, especially on the right side. Rales were only rarely heard.
b. The most striking feature being that in the majority of cases the physical signs, after remaining unchanged for some months, completely disappeared.
c. The extensive physical changes appearing on the skiagram as a dense diffuse shadow were not due to specific tuberculous tissue changes.
d. They suggested that these pathological alterations were a reaction in the adjacent lung tissue to toxins produced by a tuberculous focus. If the activity of the focus ceased these alterations might completely disappear.
e. The infiltration should be put on the same level with the perifocal inflammation which may occur in the proximity of any inflammatory focus (e.g. the inflammatory swelling round a boil).
Primary disease – First time infection with tubercle bacilli. Features are
1). Middle and lower lung zones
2). In few patients, the initial infection progresses and manifests as –
a. Rupture into pleural space causing pleural effusion
b. Extensive caseous pneumonia
c. Enlargement of LN → bronchial obstruction
d. Rupture of TB focus into a bronchus leading to endobronchial TB.
e. Rupture into a pulm blood vessel causes hematogenous spread
3). Manifestations of hypersensitivity reactions
a. Erythema nodosum
b. Phlyctenular conjunctivitis
Unilateral hilar lymphadenopathy as part of the primary complex is a characteristic feature of primary tuberculosis
Extra Edge: Primary tuberculosis
1). It is the first infection with tubercle bacilli in individuals who have not been previously exposed to the organism
2). Seen in children
3). Primary complex is characteristic
Primary (Ghon) complex
1). Unilateral enlarged hilar lymph nodes
2). Ghon focus: Epithelioid cell granulomatous inflammation (Consolidation) at site of parenchymal infection. Usually small and subpleural most commonly located under pleura in lower part of upper lobe.
3). Usually a symptomatic or manifested by a mild flu like illness at time of tuberculin conversion.
4). Fibrocaseous lesion are characteristic in primary TB.
5). Phlyctenular conjunctivitis is a feature of primary TB
1). Pleural effusion is common in primary TB
Pleural effusion is found in upto 2/3 of cases of primary TB and results from penetration of bacilli into the pleural space from an adjacent subpleural focus.
2). Cavitation is not a feature of primary TB but it is a feature of secondary TB (Robbins)
Extra Edge: Effects of primary tuberculosis
1). Tuberculin positivity.
2). Partial immunity to tuberculosis: individual requires a higher dose to be reinfected by tubercle bacilli.
3). Presence of dormant tubercle bacilli.
4). Lesions heal by fibrosis and may calcify.
5. Radiological evidence of healed primary infection may or may not be present.