Primary Complex (Ghon’s Complex)
A primary complex represents the initial site of infection by Mycobacterium tuberculosis in a previously unsensitized individual (primary tuberculosis). It is the hallmark of childhood TB.
1. Components of the Primary Complex
The classic primary complex consists of three components:
- Ghon’s Focus: The initial subpleural parenchymal lesion (usually in the mid or lower zones of the lung).
- Lymphangitis: Inflamed lymph channels draining the site.
- Regional Hilar Lymphadenopathy: Enlargement of the hilar lymph nodes draining the focus.
2. Clinical Course
- Outcome: In > 90% of children, the primary complex heals by fibrosis and calcification.
- Ranke Complex: The calcified Ghon focus plus calcified hilar lymph nodes seen on chest X-ray.
- Complications: If not contained, it can progress to lymphohematogenous spread (leading to military TB or TB meningitis) or cause endobronchial obstruction via lymph node enlargement.
NEET PG Hint: Remember that the Ghon focus is typically located in the mid or lower zones, unlike post-primary (adult) TB, which favors the apical or posterior segments of the upper lobes due to higher oxygen tension. Also, always distinguish between the Ghon focus (the parenchymal lesion) and the Ghon complex (focus + lymph nodes).