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# Granulomatous pneumonia: tuberculosis and endemic fungi

- Lesion

Tuberculosis and fungi such as Histoplasma and Paracoccidioides cause slow pneumonias made of granulomas, often with caseous necrosis, cavities and scars.

Updated Nov 12, 2026

## Key points

- Primary TB: Ghon focus (subpleural, lower part of upper lobe or upper part of lower lobe) plus hilar node = Ghon complex; calcified = Ranke complex.
- Secondary (reactivation) TB: apical and posterior upper lobes, where oxygen is high; caseous cavities that spread through bronchi.
- Miliary TB: millet-seed granulomas in lungs and other organs after blood spread; progressive primary TB in children and immunocompromised.
- Histoplasma: tiny yeasts inside macrophages; granulomas that calcify, mimicking TB; bat and bird droppings, caves.
- Paracoccidioides: large yeast with multiple buds ('pilot's wheel'); rural male workers in Latin America; lung, mouth and skin.
- Coccidioides (spherules with endospores) and Blastomyces (broad-based budding) complete the classic set.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Granulomatous lung infections: what the pathologist looks for
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes

- Study Test yourself

- Connections Connections

## What it is

Chronic pneumonia in an immunocompetent person is usually a localised granulomatous inflammation caused by Mycobacterium tuberculosis or dimorphic fungi. The lung lesion follows the same logic for all: a Th1 response builds granulomas that contain the organism, sometimes with caseous necrosis, cavitation and calcified scars. Tuberculosis, histoplasmosis and paracoccidioidomycosis are all relevant in Colombia.

## Structure

- Caseating granuloma: central cheese-like, structureless eosinophilic necrosis, epithelioid histiocytes, Langhans giant cells and a lymphocyte cuff.
- Cavity: caseous material discharged into a bronchus leaves a hole with a fibrous wall, full of bacilli.
- Miliary pattern: countless uniform small yellow-white nodules.
- Ziehl–Neelsen stain shows acid-fast bacilli; Grocott methenamine silver and PAS show fungi.

## Step by step

- Inhaled bacilli or fungal spores are engulfed by alveolar macrophages but survive inside them.
- Organisms multiply and spread to hilar nodes before immunity develops.
- After a few weeks Th1 cells release IFN-γ; activated macrophages form granulomas that contain the organism.
- Caseous necrosis forms in the centre; most primary foci heal and calcify, leaving latent organisms.
- If immunity falls (HIV, diabetes, malnutrition, steroids), organisms reactivate in the apex and cavities form.
- Erosion into a bronchus spreads disease and makes the patient contagious; erosion into vessels causes hemoptysis or miliary spread.

## Granulomatous lung infections: what the pathologist looks for

| Organism | Form in tissue | Stain | Clue |
| --- | --- | --- | --- |
| [Mycobacterium tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/) | Thin rods inside caseous granulomas | Ziehl–Neelsen (acid-fast) | Apical cavities, Ghon complex |
| [Histoplasma capsulatum](https://durgical.com/en/conditions/histoplasmosis/) | Tiny yeasts packed in macrophages | Silver, PAS | Caves, bat or bird droppings; calcified nodules |
| [Paracoccidioides](https://durgical.com/en/conditions/paracoccidioidomycosis/) | Large yeast with many buds (pilot's wheel) | Silver | Rural workers in Latin America; oral ulcers |
| [Coccidioides](https://durgical.com/en/conditions/endemic-mycoses-blastomycosis-and-coccidioidomycosis/) | Spherules full of endospores | Silver, PAS | Arid regions of the Americas |
| [Blastomyces](https://durgical.com/en/conditions/endemic-mycoses-blastomycosis-and-coccidioidomycosis/) | Thick-walled yeast with broad-based bud | Silver, PAS | Skin and bone spread |

## Markers

- Ziehl–Neelsen
- Grocott methenamine silver
- PAS
- IFN-γ release assay

## Clinical notes

- Reactivation TB: chronic cough, hemoptysis, fever, night sweats and weight loss, with upper-lobe cavities.
- Histoplasmosis is usually silent; heavy exposure or HIV causes acute or disseminated disease.
- Paracoccidioidomycosis typically presents with lung disease and painful mulberry-like oral ulcers in rural workers.
- Colombia reports thousands of TB cases each year; HIV co-infection and drug resistance are concerns.

## Memory aid

TB rises to the top where the oxygen is; Histoplasma hides in macrophages; Paracoccidioides steers a ship's wheel.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the Ghon complex?

The primary TB lesion: a subpleural Ghon focus in the mid lung plus the involved hilar lymph nodes; when calcified it is the Ranke complex.

## Why does reactivation tuberculosis favour the lung apices?

The apices have high oxygen tension, which favours growth of the aerobic bacilli.

## What is the typical tissue form of Paracoccidioides?

A large yeast with multiple narrow-based buds around it, the pilot's (ship's) wheel.

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## Elsewhere in DurgiPedia

- [Granulomatous inflammation](https://durgical.com/en/immunology/granulomatous-inflammation/)

## Connections

## Related 6

- [Granulomatous inflammation: caseating vs non-caseating, the causes to know](https://durgical.com/en/general-pathology/granulomatous-inflammation-caseating-vs-non-caseating-the-causes-to-know/)
- [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/)
- [Sarcoidosis: the lung](https://durgical.com/en/general-pathology/sarcoidosis-the-lung/)
- [Coal workers' pneumoconiosis and silicosis](https://durgical.com/en/general-pathology/coal-workers-pneumoconiosis-and-silicosis/)
- [The lung in immunocompromise and transplant](https://durgical.com/en/general-pathology/the-lung-in-immunocompromise-and-transplant/)
- [Oral infections and the mouth in systemic disease](https://durgical.com/en/general-pathology/oral-infections-and-the-mouth-in-systemic-disease/)

## Related conditions 5

- [Pulmonary tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/)
- [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/)
- [Histoplasmosis](https://durgical.com/en/conditions/histoplasmosis/)
- [Paracoccidioidomycosis](https://durgical.com/en/conditions/paracoccidioidomycosis/)
- [Endemic mycoses: blastomycosis and coccidioidomycosis](https://durgical.com/en/conditions/endemic-mycoses-blastomycosis-and-coccidioidomycosis/)

## Microorganisms 5

- [Mycobacterium tuberculosis](https://durgical.com/en/microbiology/mycobacterium-tuberculosis/)
- [Histoplasma capsulatum](https://durgical.com/en/microbiology/histoplasma-capsulatum/)
- [Paracoccidioides brasiliensis](https://durgical.com/en/microbiology/paracoccidioides-brasiliensis/)
- [Coccidioides immitis](https://durgical.com/en/microbiology/coccidioides-immitis/)
- [Blastomyces dermatitidis](https://durgical.com/en/microbiology/blastomyces-dermatitidis/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Tuberculosis](https://medlineplus.gov/tuberculosis.html) (MedlinePlus, US National Library of Medicine, 2025); [Histoplasmosis](https://medlineplus.gov/histoplasmosis.html) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/granulomatous-pneumonia-tuberculosis-and-endemic-fungi/