The radicular cyst is defined as an area of chronic inflammation exhibiting a closed central cavity surrounded by an epithelial lining.
The cyst develops–in three stages–from a pre-existing chronic apical periodontitis:
In the phase of initiation, dormant Malassezs rest cells begin to proliferate During phase 2, a central cavity lined by epithelium develops.
During the growth phase, the cyst enlarges in size as a result of osmotic and other factors that stimulate bone resorption.
The established radicular cyst consists of four components:
- The connective tissue capsule
- A subepithelial zone of chronic inflammatory infiltrate
- The epithelial cyst wall
- The cystic lumen.
In addition to desquamative, necrotic epithelial cells and cholesterol, the cystic lumen also contains inflammatory cells and debris from the resorbed osseous tissue
- Within the lumen of the radicular cyst, one observes cholesterol crystals surrounded by the epithelial cystic wall.
- The epithelial wall is a multilayered squamous epithelium.
- Within the cystic cavity, one notes cholesterol crystals, necrotic tissue, neutrophilic granulocytes, and mononuclear leukocytes.
- The remnants of lamellar bone within the cystic cavity indicate the resorptive capacity of the cystic tissues.
- Multinuclear giant cells are both an indication of a possible foreign body reaction as well as of osteoclastic activity; adjacent plasma cells produce antibodies, primarily IgG and IgA, and lesser amounts of IgM and IgE; this is an expression of an immune reaction.
- Lymphocytes are primarily T cells, less often B cells, in a ratio of 3:1.