Q&A: Is peri-apical granuloma really a granuloma?
Author: Sanketh DS, MDS
Nope, it’s not! Peri-apical granuloma is wrongly termed “granuloma” and is actually a localised mass of chronically inflamed granulation tissue! While granulation tissue and granuloma are both a product of chronic inflammation, they are entirely different types of inflammatory tissue reactions. Granuloma is a product of cell-mediated immune response, a type-IV hypersensitivity reaction caused by agents like bacteria or fungi, for example. And granulation tissue is basically the hallmark of tissue repair, a tissue that is formed when the body tries to heal itself!
In type IV hypersensitivity responses, a macrophage engulfs foreign agents, presents it to a CD 4 T lymphocyte and activates the T-cell in the process. Activated CD 4 T cell further activates more CD 4 T cells & macrophages through IL-2 and IFN-γ respectively. These activated macrophages become super active and alert, engulfing more foreign agents and further activate more CD-4 T cells by producing cytokines like IL-12. It also produces growth factors that stimulate fibrosis. This creates a feedback loop, with macrophages activating T cells and T cells activating macrophages, which can become never ending unless the offending gent is removed! The chronic feedback loop and constant activation of the macrophages by IFN-γ causes macrophages to transform into epitheloid cells (resemble epithelial cells, hence the name) and also causes fusion of adjacent macrophages to form multinucleate giant cells like Langhans giant cells and foreign body giant cells. So, granuloma essentially is a collection of epitheloid cells interspersed with giant cells surrounded by lymphocytes and fibrosis!
Peri-apical granuloma is a mass of reparative granulation tissue which forms as a defensive reaction to microbial infection seeping into the peri-apex from the overlying tooth. The periapical tissue in an attempt to heal reacts by inducing formation of a loose matrix with numerous small blood vessels and fibroblasts. It also has numerous inflammatory cells which are predominantly lymphocytes interspersed with neutrophils and plasma cells.
The lesion is usually asymptomatic, but may sometimes cause a mild pain while biting or chewing. This pain may be due to the hyperemia and inflammation in the peri-apex. The involved tooth is non-vital and does not respond to vitality tests. Peri-apical granulomas are usually diagnosed during routine radiography. They are radiolucencies which are typically < 2 cm in diameter or may be bigger occasionally. They may or may not be well circumscribed and are situated closely in association with the affected tooth. However, radiographs are not diagnostic as it is difficult to differentiate peri-apical granulomas from peri-apical cysts or abscesses.
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