Radiographic Interpretation between Periapical Cysts and Periapical Granuloma- A Diagnostic Tool
Dr. A. Sivachandran1, Dr. K. Suresh Kumar2
1Department of Oral Pathology, SRM Kattankulathur Dental College, Potheri, Potheri, Kanchipuram Dt-603203
2Department of Periodontics, Asan Memorial Dental College, Hospital, Potheri, Kanchipuram Dt-603203
Periapical radiolucencies are the commonest radiographic findings for dental practioner’s. The commonest cause of periapical cysts and periapical granulomas are well known. This article is a review of studies published on the above mentioned topic. Studies have been reported on radiographic lesion sizes of periapical lesions. However none have been reported on prevalence of subjective radiographic features in these lesions except for the early assumption that a periapical cyst usually exhibits a radiopaque cortex. The purpose of this article is to evaluate the prevalence of several subjective radiographic features of periapical cysts and granulomas in the hope to identify features that maybe suggestive of either diagnosis. The conclusion of various studies came into a nutshell as that a regular (circular or semi-circular) radiographic outline is likely to be a periapical cyst while an irregular radiographic outline is not indicative of either a cyst or a granuloma.
Many studies have been reported on radiographic lesion sizes of periapical lesions. However no studies have been reported on prevalences of subjective radiographic features in these lesions except for the early assumption that a periapical cyst usually exhibit a radiopaque cortex.
Periapical cyst: A well-circumscribed round or oval radiolucent periapical lesion with or without a sclerotic border and measuring more than 1 cm in diameter.
Periapical granuloma: A well-circumscribed radiolucent periapical lesion with or without a sclerotic border and measuring less than 1 cm in size. No studies have been reported on prevalences of subjective radiographic features in these lesions except for the early assumption that a periapical cyst usually exhibit a radiopaque cortex. This research is conducted to evaluate the prevalences of several subjective radiographic features of periapical cysts and granulomas to identify features that maybe suggestive of either diagnosis. To conclude a regular (circular or semi-circular) radiographic outline is likely to be a periapical cyst while an irregular radiographic outline is not indicative of either a cyst or a granuloma. Periapical periodontitis (also termed apical periodontitis AP, or periradicular peridontitis) is an acute or chronic inflammatory lesion around the apex of a tooth root which is caused by bacterial invasion of the pulp of the tooth. The term is derived from peri-meaning "around", apical referring to the apex of the root (the tip of the root), and –it is meaning a disease characterized by inflammation. Periapical periodontitis can be considered a sequela in the natural history of dental caries (tooth decay), irreversible pulpitis and pulpal necrosis, since it is the likely outcome of untreated dental caries, although not always. Periapical periodontitis may develop into a periapical abscess, where a collection of pus forms at the end of the root, the consequence of spread of infection from the tooth pulp (odontogenic infection), or into a periapical cyst, where an epithelial lined, fluid filled structure forms . The periapical cyst (also termed radicular cyst, and to a lesser extent dental cyst) is the most common odontogenic cyst. It is caused by pulpal necrosis secondary to dental caries or trauma. The cyst lining is derived from the cell rests of Malassez . Usually, the periapical cyst is asymptomatic, but a secondary infection can cause pain. On radiographs, it appears radiolucency (dark area) around the apex of a tooth's root. Radicular cyst is the most common odontogenic cystic lesion of inflammatory origin. It is also known as periapical cyst, apical periodontal cyst, root end cyst or dental cyst. It arises from epithelial residues in periodontal ligament as a result of inflammation. The inflammation usually follows death of dental pulp. Radicular cysts are found at root apices of involved teeth. These cysts may persist even after extraction of offending tooth; such cysts are called residual cysts. It is defined as an odontogenic cyst of inflammatory origin that is preceded by a chronic periapical granuloma and stimulation of cell rests of malassez present in the periodontal membrane. It is classified as follows:
1) Periapical Cyst:
These are the radicular cysts which are present at root apex.
2) Lateral Radicular Cyst:
These are the radicular cysts which are present at the opening of lateral accessory root canals of offending tooth.
3) Residual Cyst:
These are the radicular cysts which remain even after extraction of offending tooth .
Dental cysts are usually caused due to root infection involving the tooth affected greatly by carious decay. The resulting pulpal necrosis causes release of toxins at the apex of the tooth leading to periapical inflammation . This inflammation leads to the formation of reactive inflammatory (scar) tissue called periapical granuloma further necrosis and damage stimulates the Malassez epithelial rests, which are found in the periodontal ligament, resulting in the formation of a cyst that may be infected or sterile (The epithelium undergoes necrosis and the granuloma becomes a cyst). These lesions can grow into large lesions because they apply pressure over the bone causing resorption. The toxins released by the breakdown of granulation tissue are one of the common causes of bone resorption. These cysts are not true neoplasms
Pathogenesis of Radicular Cyst is conveniently considered in 3 Phases, which are as follows
1. Phase of Inititiation,
2. Phase of Cyst Formation,
3. Phase of Cyst Enlargement
Phase of Initiation:
It is generally agreed that the epithelial lining of these cysts are derived from epithelial cell rests of malassez in periodontal ligaments. However in some cases, epithelial lining may be derived from,
· Respiratory epithelium of Maxillary sinus when periapical lesion communicates with sinus wall.
· Oral epithelium from fistulous tract.
· Oral epithelium proliferating apically from periodontal pocket.
The mechanism of stimulation of epithelial cells to proliferate is not clear. It may be due to inflammation in periapical granuloma or some products of dead pulp may initiate the process and at same time it evokes an inflammatory reaction. There is also evidence of local changes in supporting connective tissue which may be responsible for activating the cell rests of malaseez .
Phase of Cyst Formation:
It is a process by which cavity becomes lined by proliferating epithelium. There are two theories regarding it which are as follows:
· Most widely accepted theory suggests that initial reaction leading to cyst formation is a proliferation of epithelial rests in periapical area involved by granuloma. As this proliferation continues with the epithelial mass increasing in size by division of the cells on periphery corresponding to basal layer of surface epithelium. The cells of central portion of mass become separated further and further from nutrition in comparison with basal layer due to which they fail to obtain sufficient nutrition, they eventually degenerate, become necrotic and liquify. This creates an epithelium lined cavity filled with fluid.
· Another theory suggests that a cyst may form through proliferation of epithelium to line a pre-existing cavity formed through focal necrosis and degeneration of connective tissue in periapical granuloma. But the finding of epithelium or epithelial proliferation near an area of necrosis is not common.
Phase of Cyst Enlargement:
Experimental work provided evidence that osmosis makes contribution to increase in size of cyst. Investigators found that fluids of Radicular cysts have Gamma Globulin level High by almost more than half to patient’s own serum. Plasma protein exudate and Hyaluronic acid as well as products of cell breakdown contribute to high osmotic pressure of cystic fluid on cyst walls which causes resorption of bone and enlargement of cyst. Smaller radicular cysts are usually symptomless and may be discovered when intraoral periapical (IOPA) radiographs are taken of non-vital teeth . Larger lesions show slowly enlarging swelling. At first the enlargement is bony hard but as cyst increases in size, the covering bone becomes very thin, despite subperiosteal deposition and swelling exhibits springiness, only when cyst has become completely eroded, the bone will show fluctuation. In Maxilla, there may be buccal and palatal enlargement whereas in mandible it is usually labial or buccal and only rarely lingual. Pain and infection are other clinical features of some radicular cysts. These cysts are painless unless infected. However, complain of pain is also observed in patient without any evidence of infection. Occasionally, a sinus may lead from cyst cavity to the oral mucosa. Quite often there may be more than one radicular cyst. Scientists believe that there are cyst prone individuals who show particular susceptibility to develop radicular cysts. Radicular cysts arising from deciduous tooth are very rare. Deciduous tooth which had been treated endodontically with materials containing Formecresol which in combination with tissue protein is antigenic and may elicit a humoral or cell-mediated response like rapid buccal expansion of cyst. Rarely, parasthesia or pathologic jaw bone fracture may occur. Radiographically it is virtually impossible to differentiate granuloma from a cyst. If the lesion is large it is more likely to be a cyst. Radiographically both granuloma and cyst appear radiolucent, associated with the apex of non vital tooth. Intra Oral Peri Apical Radiographs i.e. IOPAs are common radiographs which are used as diagnostic aid from radiological point of view. Radiographically, Radicular Cysts are round or ovoid radiolucent areas surrounded by a narrow radio-opaque margin, which extends from Lamina Dura of involved tooth. In infected or rapidly enlarging cysts, radio-opaque margins may not be seen. Root resorption is rare but may occur. It is often difficult to differentiate radiologically between radicular cysts and apical granulomas . Radiologic presentation of Radicular Cyst is given in detail as follows:
Periphery and Shape:
Periphery usually has a well defined cortical border. If Cyst is secondarily infected, the inflammatory reaction of surrounding bone may result in loss of this cortex or alteration of cortex into more sclerotic border. The outline of radicular cyst usually is curved or circular unless it is influenced by surrounding structures such as cortical boundaries.
In most cases, internal structure of radicular cyst is radiolucent. Occasionally, dystrophic calcification may develop in long standing cysts appearing as sparsely distributed, small particulate radio-opacities.
Effects on Surrounding Structures:
If a radicular cyst is large, displacement and resorption of roots of adjacent teeth may occur. The resorption pattern may have a curved outline. In rare cases, the cyst may resorb the roots of related non-vital teeth. The cyst may invaginate the antrum, but there should be evidence of a cortical boundary between contents of cyst and internal structure of antrum. The outer cortical plates of maxilla and mandible may expand in a curved or circular shape. Cyst may displace the mandibular alveolar nerve canal in an inferior direction .
The gross specimen may be spherical or ovoid intact cystic masses, but often they are irregular and collapsed. The walls vary from extremely thin to a thickness of about 5mm. The inner surface may be smooth or corrugated. The histopathological studies shows following features:
1) Epithelial Lining:
Almost all radicular cysts are wholly or in part lined by stratified Squamous Epithelium and range in thickness from 1 to 50 cell layers. The only exception to this is in those rare cases of periapical lesions of Maxillary Sinus. In such cases, cyst is then lined with a pseudo stratified cilliated columnar epithelium or respiratory type of epithelium. Ortho or para keratinised linings are very rarely seen inradicular cysts. Secretory cells or ciliated cells are frequently found in epithelial lining.
2) Rushton’s Hyaline Bodies:
In approximately 10% of cases of radicular cysts, Rushton's Hyaline bodies are found in epithelial linings. Very rarely they are found in Fibrous capsule. The hyaline bodies are tiny linear or arc shaped bodies which are amorphous in structure, eosinophillic in reaction and Brittle in nature.
3) Cholesterol Clefts:
Deposition of Cholesterol crystals are found in many radicular cysts, slow but considerable amount of cholesterol accumulation could occur through degeneration and disintegration of lymphocytes, plasma cells and macrophages taking part in inflammatory process, with consequent release of Cholesterol from their walls.
4) Fibrous Capsule:
Fibrous Capsule of Radicular Cyst is composed of mainly condensed parallel bundles of collagen fibres peripherally and a loose connective tissue adjacent to epithelial lining.
5) Inflammatory Cells:
Acute inflammatory cells are present when epithelium is proliferating. Chronic inflammatory cells are present in connective tissue immediately adjacent to epithelium.
6) Mast cells, Remnants of Odontogenic Epithelium and occasionally Satellite microcysts are also present. Some cysts are markedly vascularised. Various kinds of Calcifications are also present .
After detail review we come to a conclusion that periapical cyst has a well defined outline and periapical granulomas have an irregular outline.
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Accepted on 23.04.2017 © RJPT All right reserved