31. Miliary tuberculosis of the lung

Staining: HE

Overview of the slide

Organ: Lung

Description:

We can see multiple granulomas with necrotic centres. We can see some Langhans giant cells, lymphocytes, fibroblasts and epithelioid cells in the granulomas. There are some pigments present.

Diagnosis: Miliary tuberculosis

Causes:

• Infection by mycobacterium tuberculosis

Theory:

Miliary tuberculosis a subtype of primary progressive tuberculosis characterized by the bacterium spreading to multiple organs that end up forming many very small (1-2 mm) granulomas. The bacterium in this case spreads by lymph or blood. The name comes from the x-ray morphology which looks like millet seeds spread throughout the lungs.

The granulomas are soft because they contain necrotic centres. Macroscopically we can see caseous necrosis. The granulomas are more numerous in the upper lobes. This is because the upper lobes are better ventilated (see pathophysiology), and the m. tuberculosis bacterium is highly aerobic. The granulomatous inflammation in tuberculosis is due to a type 4 hypersensitivity reaction.

A soft granuloma. The eosinophilic centre in the middle is necrotic semi-fluid.

The pigments that are present can be either:

• Haemosiderin in heart failure cells
• A result of too long formalin fixation
• Anthracosis

The cellular part of the granuloma. A soup of fibrocytes, lymphocytes, epithelioid cells and giant cells.

Langhans giant cell

Heart failure cells are macrophages filled with haemosiderin due to pulmonary congestion, which causes RBCs to leak out from the capillaries.