Granulome

Granulome is a term used to describe a localized nodular inflammatory lesion characterized by granulomatous tissue. In medical literature, the more common term is granuloma; granulome is less frequently used and may appear as a synonym or historical variant. Granulomas form when the immune system attempts to wall off substances it perceives as foreign but difficult to eradicate, such as certain microbes or inert materials.

Structure and histology typically involve a core of modified macrophages called epithelioid cells, and often multinucleated giant cells, surrounded by lymphocytes. The lesion may be necrotic (caseating) or non-necrotic, and it can be encased in fibrous tissue. The exact appearance depends on the underlying cause and tissue involved.

Causes of granulomas are diverse. They include infectious agents such as Mycobacterium tuberculosis and certain fungi, as well as non-infectious inflammatory diseases like sarcoidosis and Crohn disease. Foreign bodies can also trigger granuloma formation through chronic granulomatous inflammation. Some conditions produce granulomas without a clear cause and are labeled idiopathic.

Diagnosis relies on a combination of clinical context, imaging, and tissue analysis. Biopsy with histopathology is essential, with additional tests including acid-fast staining for mycobacteria, special stains for fungi, cultures, and molecular methods (PCR) to identify the causal organism. Exclusion of infection is important in noninfectious cases.

Treatment depends on the underlying cause. Infectious granulomas require appropriate antimicrobial therapy; noninfectious granulomas may respond to corticosteroids or other immunosuppressants. Foreign body granulomas may improve with removal of the offending material. Prognosis is variable and depends on the etiology and extent of organ involvement.