Radicular cyst

Radicular Cyst
Inflammatory Odontogenic Cyst
Synonyms
Periapical cyst, apical periodontal cyst, or dental cyst
Done By:
Mahmoud Amir Alagha

Definition
A radicular cyst is a cyst that most likely results when rests of epithelial cells (Malassez) in the periodontal ligament are stimulated to proliferate and undergo cystic degeneration by inflammatory products from a non-vital tooth.

Clinical Feature
Most common type of cyst of the jaws.
Rarely seen before the age of 10.
Most frequent between 20 and 60 years.
More common in males than females 3 to 2.
Maxilla affected more than 3 times the mandible.

Clinical Feature
Cause slowly progressive painless swelling.
No symptoms until they become large enough or infected.
If infection enters, the swelling becomes painful and may rapidly expand, partly due to inflammatory edema.

Clinical Feature
The swelling is rounded and at the first hard
Later, when the bone has been reduced to egg-shell thickness, a crackling sensation (crepitant) may be felt on pressure
Finally, part of the wall is resorbed entirely away, leaving soft fluctuant (rubbery and fluctuant) swelling, bluish in color, beneath the mucous membrane.

Clinical Feature
The dead tooth from which the cyst has originated is present, and its relationship to the cyst will be apparent in a radiograph

7
Radicular cyst / pathogenesis
a Initiation b Cyst formation c Cyst enlargement

Pathogenesis & Pathology
The main factors in the pathogenesis of cyst formation are:
Proliferation of epithelial lining and fibrous capsule
Hydrostatic pressure of cyst fluid
Resorption of Surrounding bone

Pathogenesis of Cyst Formation Epithelial Proliferation
Infection from the pulp chamber induces inflammation and proliferation of the epithelial rest of Malassez.
If infection can be eliminated from the root canal, small radicular cysts (up to 1 or 2 cm diameter) may regress without surgery.

Pathogenesis of Cyst Formation Hydrostatic pressure
Radicular cyst expand in balloon-like fashion, wherever the local anatomy permits, indicates that internal pressure is a factor in their growth.
The hydrostatic pressure within cysts is about 70 cm of water and therefore higher than the capillary blood pressure.

Cystic fluid is largely inflammatory exudate and contains high concentration of proteins, some of high molecular weight which can exert osmotic pressure.
Consistent with the inflammation usually present in cyst walls, cyst fluid may contain cholesterol, breakdown products of blood cells, exfoliated epithelial cells, and fibrin.

The cyst wall does not seem to act entirely as a simple semi-permeable membrane. Low-molecular-weight proteins are present in similar concentrations to those in the plasma but there are smaller amounts of high-molecular-weight proteins.

The capillaries in the cyst wall are more permeable as a result of inflammation and contribute varying amounts of immuno-globulins and other proteins.
The net effect is that pressure is created by osmotic tension within the cyst cavity.

Pathogenesis of Cyst Formation Bone-Resorbing Factors
Experimentally, cyst tissues in culture release bone-resorbing factors.
These are predominantly prostaglandins E2 and E3.
Different types of cysts and tumors may produce different quantities of prostaglandins but if so, it is unclear whether this affects the mode of growth of the cyst.
Collagenases are present in the walls of keratocysts, but their contribution to cyst growth is also unclear.

Pathology
All stages can be seen from a periapical granuloma containing a few strands of proliferation epithelium derived from the epithelial rest of Malassez, to an enlarging cyst with a hyperplastic epithelial lining and dense inflammatory infiltrate.
Epithelial proliferation results from irritant products leaking from an infected root canal to cause periapical inflammation.

Pathology The epithelial lining
The epithelial lining consists of stratified squamous epithelium of variable thickness.
It lacks a well-defined basal cell layer and is sometimes incomplete.
Early, active epithelial proliferation is associated with obvious chronic inflammation and may then be thick, irregular and hyperplastic or appear net-like, forming rings and arcades.
Hyaline bodies may be seen in the epithelium and mucous cells are often present as a result of metaplasia.

Pathology The epithelial lining
Long-standing cysts typically have a thin flattened epithelial lining, a thick fibrous wall and minimal inflammatory infiltrate

Pathology The cyst capsule and wall
The capsule consists of collagenous fibrous connective tissue.
During active growth the capsule is vascular and infiltrated by chronic inflammatory cells adjacent to the proliferating epithelium.
Plasma cells are often prominent or predominant, and are a response to antigens leaking through the tooth apex

In a boney wall there is osteoclastic activity and resorption.
Beyond the zone of resorption these is usually active bone formation.
The net effect is that a cyst expands but retains a bony wall, even after it has extended beyond the normal bony contours.
This bony wall nevertheless becomes progressively thinner since repair is slower than resorption, until it forms a mere eggshell, then ultimately disappears altogether.

The cyst then starts to distend the soft tissues and appear as a soft bluish swelling.

Pathology Clefts
Clefts. Within the cyst capsule there are often areas split up by fine needle-shaped clefts.
These are left by cholesterol dissolved-out during preparation for sectioning.
The cholesterol is derived from breakdown of blood cells.
Small clefts are enclosed by foreign body giant cells, and extravasated red cells and blood pigment are associated.
Clefts may also be seen extending into the cyst contents but are formed in the cyst wall.

Pathology Cyst Fluid
Cyst Fluid. The fluid is usually watery and opalescent but sometimes more viscid and yellowish, and sometimes shimmers with cholesterol crystals.
A smear of this fluid may show typical notched cholesterol crystals microscopically.
Histologically, the protein content of the fluid is usually seen as amorphous eosinophilic material, often containing broken-down leucocytes and cells distended with fat globules.

In most cases the epicenter of a radicular cyst is located approximately at the apex of a nonvital tooth
Occasionally it appears on the mesial or distal surface of a tooth root, at the opening of an accessory canal or infrequently in a deep periodontal pocket
Radiographic FeaturesLocation

Note that the epicenter is apical to the lateral incisorand the presence of a peripheral cortex (arrows).

Radiographic FeaturesLocation
Most radicular cysts (60%) are found in the Maxilla, especially around incisors and canines.
Because of the distal inclination of the root, cysts that arise from the maxillary lateral incisor may invaginate the antrum.
Radicular cysts may also form in relation to a nonvital deciduous molar and be positioned buccal to the developing bicuspid.

Radiographic FeaturesPeriphery and shape
The periphery usually has a well-defined cortical border
A periapical film of a radicular cyst reveals a lesion with a well-defined cortical boundary (arrows).
Note that the presence of the inferior cortex of the mandible has influenced the circular shape of the cyst.

If the cyst becomes secondarily infected, the inflammatory reaction of the surrounding bone may result in loss of this cortex.
or alteration of the cortex into a more sclerotic border.
Note the lack of a well-defined peripheral cortex as this cyst was secondarily infected and that the root canal of the lateral incisor is abnormally wide as it is visible at the root apex.

The outline of a radicular cyst usually is curved or circular unless it is influenced by surrounding structures such as cortical boundaries.

Radiographic Features Internal structure
In most cases the internal structure of radicular cysts is radiolucent.
Occasionally, dystrophic calcification may develop in long-standing cysts, appearing as sparsely distributed, small particulate radiopacities.

Radiographic Features Effects on surrounding structures
If a radicular cyst is large, displacement and resorption of the roots of adjacent teeth may occur.
The resorption pattern may have a curved outline.
In rare cases the cyst may resorb the roots of the related non-vital tooth.
The cyst may invaginate the antrum, but there should be evidence of a cortical boundary between the contents of the cyst and the internal structure of the antrum.

Radiographic Features Effects on surrounding structures
Cysts may displace the mandibular alveolar nerve canal in an inferior direction.
The outer cortical plates of the maxilla or mandible may expand in a curved or circular shape.

A and B, Two images of a radicular cyst originating from a non-vital deciduous second molar show expansion of the buccal cortical plate to a circular or hydraulic shape (arrows) and displacement of the adjacent permanent teeth.

Radiographic InterpretationDifferential Diagnosis
Differentiation of a small radicular cyst from an apical granuloma may be difficult and in some cases impossible.
A round shape, a well-defined cortical border, and a size greater than 2 cm in diameter are more characteristic of a cyst.
An early radiolucent stage of periapical cemental dysplasia, a radiolucent apical scar, and a periapical surgical defect should also be considered in the differential diagnosis.
The patient's history helps with the differentiation. Radicular cysts that originate from the maxillary lateral incisor and are positioned between the roots of the lateral incisor and the cuspid may be difficult to differentiate from an odontogenic keratocyst or a lateral periodontal cyst.

The vitality of the involved tooth should be tested.
A non-vital tooth may have a larger pulp chamber than neighboring teeth because of the lack of secondary dentin, which normally forms with time in the pulp chamber and canal of a vital tooth

A large radicular cyst that has invaginated the maxillary antrum may collapse and start filling in with new bone.

Axial (A) and coronal (8) CT images using bone algorithm of a collapsing radicular cyst within the sinus. Note the unusual shape and the fact that new bone (arrows) is being formed from the periphery (arrows) toward the center. (Courtesy of Drs. S. Ahing and T. Blight, University of Manitoba.)

With biopsy, the histological analysis may result in an erroneous diagnosis of ossifying fibroma or a benign fibroosseous lesion. Radiographically, the important feature is that the new bone always forms first at the periphery of the cyst wall as the cyst shrinks and not in the center of the cyst; this is a different pattern of bone formation than is seen with benign fibroosseous lesions.

Diagnosis
Is based on the combination of:
Adequate History
Clinical Examination
Selected Investigation:Pulp vitality testing of associated teethRadiographs (intra/extra oral)Aspiration and analysis of cyst fluidsHistopathology

Management
Treatment of a tooth with a radicular cyst may include:
Extraction,
Endodontic therapy,
Apical surgery (Enucleation/Marsupilisation)

Endodontic therapy
If the involved non-vital tooth is to be retained, conventional intra-canal endodontic treatment will often lead to resolution of very small radicular cyst.
The radiographic appearance of the periapical area of an endodontically treated tooth should be checked periodically to make sure that normal healing is occurring.
Characteristically, new bone grows into the defect from the periphery, sometimes resulting in a radiating pattern resembling the spokes of a wheel. However, in a few cases normal bone may not fill the defect, especially if a secondary infection or a considerable amount of bone destruction occurred.

Endodontic therapy
Recurrence of a radicular cyst is unlikely if it has been removed completely.
A radicular cyst that is healing after endodontic treatment. Arrows show the original outline of the cyst; note that the new bone grows toward the center from the periphery.

If the cyst of such a size that is unlikely to resolve with endodontic treatment alone, surgery is indicated (enucleation or marsupialisation)

Enucleation
Enucleation. Complete removal of the cyst.All the cyst tissue is available for histological examination and the cyst cavity will usually heal uneventfully with minimal aftercare.
It is potentially problematic when the cyst involves the apices of adjacent vital teeth, as the surgery may deprive the teeth of their blood supply and render them non-vital.

Marsupialisation
Marsupialisation. Is a partial removal of the cyst. It is indicated in large cysts that involves the apices of adjacent teeth.
This treatment require considerable aftercare and good patient cooperation in keeping the cavity clean whilst is resolves.
In order to keep the cavity open, a ‘bung’ or acrylic plug is usually inserted in the opening, often attached to a denture or acrylic splint.

Marsupialisation
The bung stops food collecting in the cavity, but the cavity must still be syringed by the patient after each meal.
Marsupialised cyst cavities may take up to 6 months to close down to the extent of becoming ‘self-cleansing’.
Disadvantage. Not all the cyst lining is available to histopathological examination, and this may lead to misdiagnosis.

Sources
CAWSON’S Essentials of Oral Pathology and Oral Medicine 7th Edition
Oral Radiology Principles and Interpretation 5th Edition (White . Pharoah)
Oral and Maxillofacial Medicine (Crispian Scully CBE)
Color Atlas of Dental Medicine, Radiology. (Friedrich A. Pasler)

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Radicular cyst

by Mahmoud Amir Alagha

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