Periapical cyst

Other names: Radicular cyst, apical periodontal cyst, root end cyst The periapical (radicular) cyst is the most common odontogenic cyst. The usual etiology is an infected tooth, leading to necrosis of the pulp. Toxins exit at the apex of the tooth, leading to periapical inflammation. This inflammation stimulates the epithelial rests of Malassez, which are found in the apical periodontal ligament, resulting in the formation of a periapical granuloma that may be infected or sterile. Eventually, this epithelium undergoes necrosis caused by a lack of blood supply, and the granuloma becomes a cyst (periapical cyst). The lesions are not usually clinically detectable when small but most often are discovered as an incidental findings on radiographic survey.

Pathogenesis

This cyst is classified as inflammatory, because in the majority of cases it is a consequence to pulpal necrosis following caries, with an associated periapical inflammatory response. Other causes include any event that may result in pulpal necrosis such as tooth fracture and improper restorations, among others. The first line of defense to pulpal necrosis in the periapical area is the formation of a granuloma. A granuloma is a highly vascularized tissue containing a profuse infiltrate of immunologically competent cells, i.e. lymphocytes, macrophages and plasma cells.

The epithelial rests of Malassez, which are pluripotential in nature can differentiate into any type of epithelium, under the proper stimuli. These rests play a central role in the formation of radicular cysts. In the midst of the rich vascular area provided by the periapical granuloma, the rests of Malassez proliferate and eventually form a large mass of cells. With continuous growth, the inner cells of the mass are deprived of nourishment and they undergo liquefaction necrosis. This leads to the formation of a cavity which is located in the center of the granuloma, giving rise to a radicular cyst.

Islands of squamous epithelium which have developed from odontogenic rests of Malassez can also be found in a periapical granuloma without cystic transformation. Endodontists refer to these granulomas as ‘bay cyst’.

Clinical Features

Visual image of the face of the person shown on the CT scan below. Swelling can be observed in the right cheek.

Around 60% of all jaw cysts are radicular or residual cysts. Radicular cysts can occur in the periapical area of any teeth, at any age but are seldom seen associated with the primary dentition. The majority of cases of apical periodontal cysts are asymptomatic. The tooth is seldom painful or even sensitive to percussion. This type of cyst is only infrequently of such a size that it destroys much bone, and even more rarely does it produce expansion of the cortical plates. The apical periodontal cyst is a lesion that represents a chronic inflammatory process and develops only over a prolonged period of time. In some cases, such a cyst of long standing may undergo an acute exacerbation of the inflammatory process and develop rapidly into an abscess (periapical abscess) that may then proceed to a cellulitis or form a draining fistula. The cause of such a sudden flare up is not known, but it may be a result of loss of local or generalized tissue resistance.

Radiographic Features

The radiographic image of the radicular cyst is a peri- or para-apical, round or oval radiolucency of variable size which is generally well delineated and most likely with a marked radiopaque rim. Other lesions, such as granulomas, neoplasms of various origin and some diseases of bone can also present a similar radiolucent periapical appearance. Therefore, a periapical radiolucency cannot be automatically assumed to be a cyst. Several studies have indicated that it is not possible to rely on the radiographic size of a periapical radiolucency to establish the diagnosis of either cyst or granuloma unless the lesion is larger than 2 cm in diameter. Rarely radicular cysts will induce resorption of the root of the affected tooth.

CT scan of above person through head showing a right periapical cyst

Histologic Features

Microscopically a radicular cyst is limited by a mature collagenous connective tissue wall. Abundant fibroblasts can be identified within the cystic wall. The wall generally presents an inflammatory infiltrate of variable degree. Lymphocytes are generally the most prominent cells in the infiltrate and are characterized by their darkly stained nucleus, which occupies most of the cytoplasm. Plasma cells are also abundant in cysts’ walls and mostly seen in long standing (chronic) cysts. They are characterized by an eccentric nucleus with a cartwheel arrangement of the nuclear chromatin. Plasma cells are considered repertoire of immunoglobulins. Other histological findings within the cystic wall are: erythrocytes and areas of hemorrhage, occasional spicules of dystrophic bone, multinucleated giant cells and cholesterol crystals.

The cavity of a radicular cyst is generally lined by stratified squamous epithelium. These cysts can be lined by respiratory epithelium, especially if they are in the vicinity of the maxillary sinus. The epithelial lining, many times, is discontinuous, frequently missing over areas of intense inflammation. Rarely radicular cysts may be lined by mucus producing epithelium in either maxillary or mandibular locations. The mucous epithelium is the result of metaplastic transformation of the epithelial rests of Malassez which are pluripotential. In rare instances, carcinoma has been reported developing from the lining epithelium of odontogenic cysts, including the radicular cyst.

Hyaline body or Rushton body, often found in great numbers in the epithelium of apical, periodontal or residual cysts. These hyaline bodies are tiny linear or arc-shaped bodies, generally associated with the lining epithelium, that appear amorphous in structure, eosinophilic in reaction and brittle in nature, since they evidence fracture in some cases. Their frequency of occurrence in cyst linings ranges between 2.6 and 9.5% of cysts, according to a review by Allison. The etiology, pathogenesis, and significance of these structures are unknown. The lumen of the cyst usually contains a fluid with a low concentration of protein that stains palely eosinophilic. Occasionally the lumen may contain a great deal of cholesterol, and in rare instances, limited amounts of keratin are present.

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  Histopathology of a periapical cyst, with metaplastic changes of mucous secreting cells(B), and ciliated cells(C)

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  Histopathology of cholesterol clefts of a periapical cyst of the jaw

Treatment

The treatment of the radicular cyst consists of extraction of the involved teeth and careful curettage of the periapical tissue. Under some conditions, root canal therapy may be carried out with apicoectomy of the cystic lesion. The cyst does not recur if surgical removal is thorough. If the cystic sac is badly fragmented, leaving epithelial remnants, or if a periapical granuloma is incompletely removed with epithelial rests remaining, a residual cyst may develop in this area months or even years later. If untreated, the radicular cyst slowly increases in size at the expense of the surrounding bone. The bone undergoes resorption, but seldom is there a remarkable expansion of the cortical plates, as is frequently seen in the case of the dentigerous cyst.

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Source: Data courtesy of the U.S. National Library of Medicine. Since the data might have changed, please query MeSH on Periapical cyst for any updates.

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