<aside>

Ghon’s focus is a small, subpleural granulomatous lesion in the mid-lung zones, typically in the lower part of the upper lobe or upper part of the lower lobe, representing the primary site of infection in pulmonary tuberculosis (TB) following initial inhalation of Mycobacterium tuberculosis.

</aside>

When it is associated with ipsilateral hilar lymphadenopathy, it forms the Ghon complex, also known as the primary complex of Ranke.

Etiopathogenesis

Pathogen: Mycobacterium tuberculosis.
Transmission: Inhalation of aerosolized droplets containing the bacilli.
Pathogenesis:
1. Bacilli are inhaled and reach the terminal airspaces.
2. Host immune response forms granulomas with central caseous necrosis.
3. The initial site of pulmonary infection = Ghon focus.
4. Spread to regional hilar/mediastinal lymph nodes = Ghon complex.
5. If healed and calcified, forms Ranke complex.
Common Location:
- Subpleural region of upper part of lower lobe or lower part of upper lobe.
- Typically on the right side (due to bronchial anatomy).

Histology

Granulomatous inflammation with:
- Epithelioid histiocytes.
- Langhans-type giant cells.
- Central caseous necrosis.

Radiology

Modality	Imaging features
XR	Early stage: May be radiolucent or non-specific.
Late stage:
• Ill-defined subpleural consolidation or nodule.
• Hilar lymphadenopathy.
• Calcification (chronic stage).
CT	• Small nodular lesion near pleura.
• Central low attenuation (caseation).
• Enlarged and possibly calcified hilar or mediastinal lymph nodes.

Ghon complex. | Image courtesy S Bhimji MD

Differentials

Healed varicella pneumonia
Calcified hamartoma
Residual fungal granuloma