Paper II
Question
Discuss the morphological appearance of Primary pulmonary tuberculosis.
Answer
Primary pulmonary tuberculosis occurs in a previously unexposed individual, typically in childhood.
Gross/morphological findings
- Ghon focus: A single, 1–1.5 cm, grey-white subpleural focus of caseous necrosis, typically in the lower part of the upper lobe or upper part of the lower lobe (site of highest airflow/oxygenation)
- Ghon complex: The combination of the Ghon focus plus caseous necrosis in the draining hilar/mediastinal lymph nodes, reflecting lymphatic spread of bacilli from the initial focus before the immune response was established
Microscopic findings
- Classic caseating granuloma: central area of caseous (cheese-like) necrosis surrounded by epithelioid macrophages, Langhans giant cells (multinucleated, peripherally arranged nuclei), and a peripheral cuff of lymphocytes
- Ziehl-Neelsen stain may demonstrate acid-fast bacilli within the necrotic centre
Outcomes
- In most immunocompetent individuals, the primary complex heals by fibrosis and calcification (visible radiologically), with dormant bacilli potentially persisting for years (latent infection risk of later reactivation)
- Progressive primary tuberculosis: In malnourished/immunocompromised individuals, the lesion can progress directly to active disease
- Miliary tuberculosis: Haematogenous dissemination can produce widespread small granulomas across multiple organs