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Pulmonary Pathology Online

Pathology of Infectious Granulomas of the Lung

Dr Sampurna Roy MD                         


Pathology Poster of the Day: Granulomatous Pneumonia From Infection



Infections are a common cause of granulomatous lung disease. 


Granulomas may present as a nodular mass of the lung but may be spread diffusely through the lung.

Infectious agents causing granulomatous lung diseases are as follows:


Mycobacterium Tuberculosis

Atypical Mycobacterial Infection


Histoplasmosis (Histoplasma Capsulatum)




Filamentous bacteria:                 



Other Organism:

Pneumocystis Carinii



Certain features may be present which support a diagnosis of infection:


- Most important feature is necrosis, but less so if the "necrosis" is no more than some degenerative change in collagen.


- If the necrotic center contains neutrophils, the index of suspicion for infection should be especially high .


Pathologists should search for fungal infection.


- Most necrotizing granulomas are related to infection.


- Special Stains:   In a few cases the organisms may be visible on the H & E stained section.


Special stains like Ziehl- Neelsen (ZN) stain for microbacteria and Grocott’s Methenamine Silver (GMS) stain for fungi.


Grocott’s  Methenamine Silver (GMS):  Advantage and disadvantage of GMS:  GMS is much more reliable than PAS for staining fungi.  


Black/lung debris/pigment are usually distinguishable by being more heterogenous than fungal spores and may confuse the picture on the GMS.  


In this case PAS is helpful.


- Tissue necrosis and a vasculitis are commonly seen in infections. [Differential diagnosis:-  Pulmonary angiitis / granulomatosis (Wegener’s granulomatosis etc ].


Such vasculitis is usually non-necrotising, showing mural/intimal infiltration by lymphocytes and other mononuclear cells.


- In Chronic Granulomatous Disease, an inherited group of conditions characterized by abnormal phagocytic cell function, necrotizing granulomas occur with a number of infectious pathogens.

- Microorganisms are generally found most frequently in an extracellular location within the debris of the necrotic granuloma center, and not in the cellular rim.

- In mycobacterial infection, microorganisms may be relatively few and far between, requiring thorough searching of one or two adequately stained sections.

Despite the higher index of suspicion and endless staining/searching nothing may be found.

- A significant proportion of infectious granulomas (proven some other way), and almost one third of radiographically solitary granulomatous lesions, will be negative on special staining.

Therefore a lack of organisms does not exclude an infectious etiology.

In such circumstances, the pathologist can describe the lesion, and convey the suspicion, but indicate the lack of stainable microorganisms.

- If granulomatous inflammation, especially in association with  necrosis, is found in an otherwise typical nodular fibrous lesion of silicosis , the index of suspicion of a complicating mycobacterial infection should be very high.

- Obviously, in any case, if fresh material is available (Autopsy /Open/ Thoracoscopic lung biopsy), and the possibility of infection is suspected , tissue should be sent for microbiological examination for appropriate culture.

Serology, particularly in some of the fungal infections, may also provide useful information.

Further reading:

[Differential diagnosis and etiology of epitheloid cell granulomatosis of the lung].

[Anatomopathology of pulmonary granulomatoses].

Pulmonary sarcoidosis: a mimic of respiratory infection.




Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)


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