Radicular cyst: Clinical features, radiology and histopathology

Radicular or periapical cyst, is the most
common inflammatory cyst arising due to the proliferation of the epithelial rests in the
periodontal ligament. This proliferation is a result of the inflammation induced by bacteria and necrotic products seeping into the periapex through the infected pulp. Hence radicular cysts are most often found in the apices of infected teeth or sometimes in the lateral aspects of roots, when the
inflammation spreads through the lateral canals. Radicular cysts are the most common cysts occurring in the oral cavity, representing 50 – 60 % of all jaw cysts. These cysts can occur at any age but appear to peak in the 3rd to the 6th decade. Radicular cysts can occur in any tooth that is infected but appears to be frequently associated with maxillary anterior region followed by
maxillary posterior region, mandibular posterior region and the mandibular anterior region. The associated tooth is either deeply carious or restored, is always non-vital and does not respond to pulp testing. These cysts are usually asymptomatic and are discovered most often only in radiographs. They are rarely painful and may sometimes enlarge and cause swelling of the jaw. In spite of the fact that radicular cysts
arise from infected, carious teeth, it is interesting to note that there are relatively less number of radicular cysts as compared to the huge number of carious teeth. This has lead some researchers to hypothesize that there may be radicular cyst prone individuals who may either have a genetic susceptibility to cyst formation or defective immune mechanism that does not suppress cyst formation. Another interesting fact is the relatively
less number of radicular cysts associated with deciduous teeth as compared to those occurring in the permanent dentition. Radicular cyst usually shows a round to ovoid periapical radiolucency that is well corticated with a radiopaque rim. Root resorption may be observed and the lamina dura around the associated tooth is lost. Although radicular cysts are bigger in size
compared to periapical granulomas, it is nevertheless not possible to distinguish between the two based on their size on radiographs. Under the microscope, a radicular cyst consists of 3 components – 1) the central cavity (lumen), 2) the epithelial lining and 3) the cyst wall/capsule. The epithelial lining is stratified squamous and of variable thickness, usually 6-20 cell layers thick. The epithelium lining is proliferative and
may and show an arcading pattern when associated with intense inflammation in the underlying connective tissue. There are also areas of epithelium which may not show arcading and show simple stratified squamous epithelium. Metaplasia of the epithelial cells may be
observed in the form of mucus cells and ciliated cells. Ciliated cells are often noted in radicular
cysts occurring in the maxilla where they are speculated to be derived from the maxillary sinus epithelial lining. Characteristic eosinophilic structures called Rushton or hyaline bodies are found in approximately 10% of cases. These structures may be linear, concentric, curved or hairpin shaped and are hypothesized to be keratinaceous
in nature or hematogenous in origin, but the most accepted theory is that it they are secretions of the odontogenic epithelium. The cyst wall/capsule is the connective tissue comprising of collagen, numerous blood vessels and characteristic dense inflammation. Inflammation comprise of chronic inflammatory cells like lymphocytes and plasma cells. Many radicular cysts show focal areas of numerous clefts called cholesterol clefts. These cholesterol clefts are associated with a dense aggregation of giant cells. Cholesterol clefts are formed due to accumulation of cholesterol which then gets dissolved out during histologic preparations forming clefts. These cholesterol accumulations are hypothesized to be derived from the cell walls of disintegrating red blood cells, lymphocytes, plasma cells
and macrophages. Based on the relationship a radicular cyst
shares with its associated tooth, there are two types of radicular cysts. One type has a lumen or a cavity totally enclosed by the epithelial lining and this type is called the “apical true cyst”. The second type has its lumen or cavity, in continuity with the root canal, meaning, this cyst has its epithelium attaching with the
root apex, and is continuous with the root canal through its open lumen. This type is called the “apical pocket cyst”
or “bay cyst”. Since this cyst is open it continues to grow, as long as bacteria and necrotic debris continue to seep through the canal and would definitely regress and disappear on extracting or endodontically treating the tooth. The “apical true cyst”, however is self-sustaining and could continue to grow if not curetted thoroughly. Extraction of the tooth with curettage of
the periapical tissue or a thorough root canal therapy of the associated tooth is the treatment of choice. If the size of the lesion is too big for conventional endodontic therapy, an endodontic surgery is performed and the cyst removed.

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