Periapical Cyst: Etiology, Anatomy, Clinical Presentation, and Treatment Methods

Periapical cyst is a pathologic cavity in the apex of the root of the tooth, with liquid contents and a lining of non-orogenic multilayered squamous epithelium, is a type of chronic apical periodontitis.

Etiology

The cause of periapical cyst formation is microbial infection in the root canal system of the tooth. The main cells involved in the formation of this type of lesion are chronic inflammatory cells and epithelial cells of Malasse islets, which are remnants of the epithelium of the root sheath of Gertwig during tooth formation. These epithelial cells may be regarded as unipotent stem cells.

During the inflammatory response in the periapical tissues, growth factors and cytokines are released, stimulating proliferation of the epithelial rests of Malassez.

There are several theories for the formation of apical cysts.

Nutrient deficiency theory

As the epithelial islets grow, the central cells are removed from the source of nutrients and begin to undergo necrosis. Tissue decay products attract granulocytes and neutrophils to the necrosis zone, and microcavities form, which then merge to form a cystic cavity lined with multilayered squamous epithelium.

Abscess theory

When an abscess forms in connective tissue, there is a proliferation of epithelial cells that cover the abscess cavity because they tend to fill open areas of connective tissue.

Theory of fusion of epithelial strands (inflammatory hyperplasia)

Epithelial tissue in the form of chaotically directed strands in the apical granuloma proliferates, epithelial strands unite to form a three-dimensional spherical structure of fibrovascular connective tissue, in which inflammatory cells are present; further, due to insufficient blood supply, it degenerates and a cyst cavity is formed. The cystic fluid is formed from the capillary network of the granuloma by transudation and exudation of the liquid part of the blood and as a result of the decay of the formal elements.

The cells of the epithelial lining of the cyst cavity are incapable of proliferation on their own without stimulation by cytokines and growth factors.

Cysts may slowly increase in size over time, probably due to degradation of the fibrous connective tissue capsule, matrix metalloproteinases, and resorption of surrounding bone. Inflammatory mediators and cytokines stimulate epithelial cell proliferation and also mediate bone resorption in foci of apical periodontitis. Epithelial rests of Malassez may also secrete factors that promote bone resorption.

By affecting the surrounding structures, the cyst can push the roots of surrounding teeth, cause external resorption of tooth roots, push back and deform the wall of the maxillary sinus, or destroy it and penetrate directly into the sinus. In the absence of therapy periapical cysts can destroy a significant part of the adjacent bone tissue. In this case, the process may spread to the body and branch of the mandible, pathologic fracture of the mandible. Abscessing of the cyst may also occur over time.

Classification

• Periapical true cyst: its lumen is completely enclosed by an epithelial lining and has no connection with the root canal.
• Periapical pocket cyst (bay cyst, pouch-like cyst): its lumen communicates with the root canal of the affected tooth.

Anatomy

The affected tooth may be observed in the affected tooth:

• a deep carious lesion penetrating into the dental pulp;
• failed tooth restoration adjacent to pulp tissue;
• signs of trauma (cracks, chipped dentin, exposed part of the pulp).

The pulp of the tooth is necrotic, yellowish-gray or gray-black in color. The periapical region contains an area of destruction involving the periodontal ligament and surrounding bone. The periapical cyst itself is round or oval in shape, located in the area of the apex of the tooth root, and consists of the following elements:

• A connective tissue capsule containing all the cellular elements found in apical granulomas;
• Epithelial lining represented by hyperplasic neorhizal multilayered squamous epithelium. The lining may be continuous or discontinuous and may be entirely absent in some areas. Sometimes the lining is represented by the mesenteric epithelium. Both the lining epithelium and the capsule are usually infiltrated with inflammatory cells;
• The cystic cavity (lumen) contains straw-colored, opalescent fluid that may contain inflammatory exudate, cholesterol crystals, necrotic epithelial cells, remnants of resorbed bone, or bacterial colonies.

Diagnosis

• Collection of complaints and history;
• Clinical methods: visual inspection, percussion, palpation along the transitional fold;
• Thermoprobe, electroodontodiagnostics;
• Radiography (intraoral contact radiography, radiovisiography, orthopantomography, cone-beam computed tomography): carious cavity, restoration or traumatic defect penetrating into the pulp chamber, in the region of the apex of the root of the tooth, a radiopaque area of round or oval shape, with clear boundaries, a radiopaque rim may be observed around the periphery. The roots of teeth adjacent to the lesion may be displaced or shortened.

To date, there are no non-invasive diagnostic tools available to accurately differentiate a granuloma from a cyst. The size of the lumen at the apex of the root on radiographs can be used only indirectly: if the size is between 10 and 20 mm, the probability of a cyst is up to 60%; if the size is more than 200 mm2, the probability is close to 100%. However, the final diagnosis is possible only after surgical biopsy or tooth extraction.

Clinical Manifestations

As a rule, the patient does not present any complaints. Most often cysts are an incidental finding on radiologic examination. The patient may complain of swelling on the lower or upper jaw, on the vestibular or palatal side. Visualization of the tooth reveals a deep carious cavity, restoration or traumatic defect penetrating into the pulp chamber. Tooth percussion is painless, as is palpation of the mucobuccal fold.

There may be a hemispherical jaw swelling, dense and painless on palpation, the mucous membrane in this area without visible pathologic changes. If the cortical plate in the area of the lesion is thinned, there may be bone crepitation in the area of the bulge when pressure is applied. If the cortical lamina of the jaw is destroyed, palpatory percussion of the causative tooth in the projection of the root apex may be felt. If the cyst is localized in the region of the maxillary incisors, the lower wall of the nasal cavity may swell (Gerber’s roll).

The causative tooth does not respond to temperature and electrical stimuli (an important diagnostic criterion in the presence of radiologic lucency in the periapical region of several teeth).

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Treatment

To date, there is no direct evidence whether periapical cyst regression can occur after nonsurgical endodontic treatment. Considering possible pathogenetic mechanisms, epithelial growth may cease upon the removal of the stimulating bacterial factor, such as after endodontic treatment. Subsequently, the epithelial lining may thin or disappear, creating conditions for healing.

Thus, the first stage is the endodontic treatment of the tooth: extirpation of non-viable pulp or removal of old filling material from the root canals, their instrumentation and drug treatment. In the course of instrumental treatment of the canals, intracanalicular puncture of the cyst is performed according to the indications. The root canals are subsequently obturated to achieve a hermetic seal, followed by restoration of the tooth.

In the presence of a large cyst (more than 3 cm), decompression may be performed according to the indications: reduction of the cyst size by surgical incision through the cyst wall and insertion of a drain, or extracanalicular aspiration and irrigation by puncturing the cyst with two large-diameter needles, aspiration of the contents and lavage with sterile saline solution.

If the periapical lesion subsequently fails to heal, cyst enucleation may be required. This may be performed by periapical curettage, root-end resection with retrograde filling, or root amputation with simultaneous removal of the cyst lining.

If the prognosis of endodontic treatment or periapical surgery is unsatisfactory, the tooth should be extracted.