Comparative evaluation of immunohistochemistry, histopathology and conventional radiography in differentiating periapical lesions.

BACKGROUND AND AIM: Periapical lesions often present differently on the radiograph resulting in a dilemma in the mind of the dentist to arrive at a final diagnosis. Although, histopathologic diagnosis has been used for confirmation of the true nature of periapical lesion, the concept of transformation of periapical granulomas containing epithelium without cystification into cyst remains controversial. The aim of this in vivo study was to evaluate the efficacy of conventional radiography and histopathology in differentiating periapical lesions in adjunct with immunohistochemical analysis. AIM: Periapical lesions often present differently on the radiograph resulting in a dilemma in the mind of the dentist to arrive at a final diagnosis. Although, histopathologic diagnosis has been used for confirmation of the true nature of periapical lesion, the concept of transformation of periapical granulomas containing epithelium without cystification into cyst remains controversial. The aim of this in vivo study was to evaluate the efficacy of conventional radiography and histopathology in differentiating periapical lesions in adjunct with immunohistochemical analysis. MATERIALS AND
METHOD: Thirty patients having large periapical radiolucency that do not heal successfully with routine endodontic therapy in relation to either maxillary or mandibular anterior teeth were selected for the study. Intraoral periapical radiographs were obtained and provisional diagnosis of the apical areas were made. Endodontic surgery was performed to enable histopathogical investigation. The histopathological interpretation was done to arrive at a final diagnosis and selected questionable granulomas were subjected for cytokeratin (CK-14) stain.
RESULTS: The histopathological profile of lesions consisted of 66.66% periapical granulomas, 10% cysts, 6.67% abscess and 16.67% granulomas with cystic potential. The radiographic and histopathologic correlation was found in only 30% of these cases. Strong CK-14 expression was observed in all five cases of periapical granuloma with cystic potential.
CONCLUSION: The radiographic diagnosis of periapical lesions remains inconclusive. Although histopathologic examination of periapical lesions gives true nature, the precise nature of subsets of periapical granulomas may be achieved with adjunct use of immunohistochemical markers.

INTRODUCTION

A periapical lesion is a lesion involving the apical area of the tooth. The initial response of the dental pulp to injury is not significantly different from that seen in other tissues. However, the final result can be dramatically different because of rigid dentinal walls of the pulp chamber, which leads to the formation of periapical lesions, which comprises one of the most common infections seen in the oral cavity. Periapical lesions are not caused by microbial infection alone but also by other primary and independent cofactors, such as necrotic pulp, stagnant tissue fluid or root canal fillings.[1]

Imaging techniques play a very important role in the specialty of endodontics. Periapical lesions accompanying endodontic infections are usually diagnosed and treated based on the initial radiographic findings.[2] There have been reports in the literature over the attempts to make a differential diagnosis between cyst and a granuloma based on the radiological features: A cystic image would exhibit well defined margins with hyperostotic borders whereas the granuloma shows indistinct borders.

It is generally accepted that the etiology of periapical lesions is derived from the presence and colonization of bacteria in the root canal system. Microorganisms always present themselves in co-aggregation with each other and play a significant role in the ecological regulation and eventual development of an endodontic habitat adapted poly-microbial flora.[3]

Teeth with pulpal involvement and associated with large periapical radiolucency, that do not heal successfully with routine endodontic therapy are subjected to endodontic surgical procedures to completely eliminate the periapical lesion, thereby allowing complete resolution of the lesion and bone growth.

Teeth with periapical lesion often diagnosed as cyst or granuloma or abscess on radiological findings may not be the same. Therefore it is necessary to send the curetted periapical specimen for histopathological examination, to determine the true nature of the lesion.

Although the presence of cystic cavity with lining is considered to be diagnostic of periapical cyst, the presence of proliferating epithelium without cystic cavity is also considered to be potential to transform into periapical cyst. A subset of periapical granuloma with epithelium is designated to be early cystic changes or potential cystic changes. Attempts have been made in this regard to elucidate the nature of epithelium using various immunohistochemical markers like cytokeratins.

This study was carried out to compare the differentiation of the periapical lesions by both conventional radiography and histopathologic examination in adjunct with the immunohistochemical analysis and also attempts to find a possible co-relation between the conventional radiographic techniques.

MATERIALS AND METHODS

Ethical clearance was obtained from the institutional ethical committee. Informed consent of each patient was obtained after explaining the clinical procedures and the risks involved.

Thirty patients were selected for the study which included teeth with pulpal involvement and associated with large periapical radiolucency i.e. 6 mm to 25 mm, that do not heal successfully with routine endodontic therapy (symptomatic even after three months follow-up) in relation to either maxillary or mandibular anterior teeth.

METHODOLOGY

Intraoral periapical (IOPA) radiographs were taken using a bisecting angle technique. The clinical data was not disclosed to the two experienced and specialist observers, and were asked to make a detailed description of the periapical lesions including the size of the lesion mesio-distally and superior-inferiorly.

Access cavity preparation, working length determination, thorough chemo-mechanical preparation was done using K files. The root canal space was obturated using standardized gutta percha points. The cavity was then sealed with cavit. (3M ESPE Dental St. Paul, MN USA)

Local anesthesia was achieved and a full thickness trapezoidal flap was reflected by placing an incision from the marginal gingiva to the depth of the vestibule. A surgical curette was used to remove each specimen, which was immediately placed in 10% buffered formalin solution. The specimen was later sent for histopathological examination which was subjected to routine H & E staining. Depending on the diagnosis, if required the samples were subjected to immunohistochemical analysis by employing CK-14 stain.

The statistical analysis was done using Z-test for proportions with SPSS13 version.

RESULTS

A total of thirty patients were selected for the study. They were distributed according to various study groups. The sex distribution revealed that twenty cases were males and remaining were females. The lesions were divided into five different age groups. The lesions obtained were maximum in age range of 20-29 years. 90% of the lesions were found in the maxilla.

The radiographs were viewed and four cases were diagnosed as periapical abscess [Figure 1a], eleven cases as periapical granuloma [Figure 1b] and fifteen cases as periapical cyst [Figure 1c] corresponding to 13.33%, 36.67% and 50% respectively. The lesions were measured mesio-distally and superio-inferiorly. The mean mesio-distal measurement was 9.47mm and its standard deviation 4.3mm. The mean superio-inferior measurement was 10.07mm and its standard deviation 4.2mm.

Figure 1

Intraoral Periapical Radiographs showing (a) Periapical Abscess; (b) Periapical Granuloma; (c) Periapical Cyst

The obtained Haematoxylin and Eosin stained sections of periapical lesions were evaluated histopathologically and assessed by Spearman's rank order co-relation test. Two cases were diagnosed as periapical abscess [Figure 2a], twenty cases as periapical granuloma [Figure 2b], five cases as periapical granuloma with cystic potential [Figure 2c] and three cases as periapical cyst [Figure 2d] corresponding to 6.67%, 66.67%, 16.67% and 10% respectively.

Figure 2

Photomicrographs showing histopathologic picture of (a) Periapical Abscess; (b) Periapical Granuloma; (c) Periapical Granuloma with cystic potential, the arrows indicating epithelial lining with suttle clefting; (d) Periapical Cyst, the arrows indicating the epithelial lining

Five cases of periapical granuloma with cystic potential on immunohistochemical analysis with CK-14 stain confirmed that all the samples were developing periapical cysts [Figure 3b]. One case of periapical granuloma and one case of periapical cyst were used as negative control and positive control respectively [Figure 3a,c].

Figure 3

Photomicrograph of CK-14 staining showing (a) Negative expression in Periapical Granuloma; (b) and (c) Strong positive expression in Periapical Granuloma with cystic potential and Periapical Cyst

The possible correlation between radiographic and histopathologic findings was calculated using Spearman's rank order co-relation study [Figure 4]. The calculations showed that the co-relation between radiography and histopathology is not statistically significant in most of the cases. There was co-relation in only nine cases (30%) of the total samples of which seven were periapical granuloma and two were periapical cyst.

Figure 4

Graph representing the co-relation between radiographic and histopathologic observations

The comparison of results from radiograph and histopathology was done using Z test for proportions (P < 0.05) which indicated the difference in proportions was significant in the cases of periapical granuloma, periapical granuloma with cystic potential and periapical cyst [Table 1].

Table 1

Comparison of results from radiography and histopathology

DISCUSSION

Successful root canal therapy includes proper diagnosis, ideal access cavity preparation, thorough chemo-mechanical preparation and a three dimensional obturation with an impermeable seal.

The development and persistence of periapical inflammation after completion of root canal treatment can be attributed to a number of factors such as toxic materials, remaining necrotic tissue, bacterial infection or a combination of these. These factors are capable of inducing non-specific inflammatory and/or specific immunologic reactions in the periradicular tissues.[456] Various studies have indicated that 75% to 95% of the teeth requiring endodontic treatment can be successfully treated conservatively. The remaining non-resolving fraction of periapical lesions should be treated surgically.[7] The principal modality available to manage failure of conventional orthograde endodontic treatment for a large nonhealing periapical lesion is apical surgery with the success rate being 86-92%.[8]

Endodontic diagnosis depends most commonly on patient's history, radiographs and vitality testing. Radiographs aid the clinician in diagnosing the lesion during intra or inter-operative procedures as well as post-operative evaluation following root canal treatment. The radiographic method can only depict the location and the size of the periapical lesion and not the exact nature of the pathology. Priebe et al in their study concluded that out of 55 lesions, only 13% were diagnosed as periapical cysts and 59% of the 46 lesions were diagnosed as periapical granulomas and abscesses.[9] The problem of unreliability in the radiographic interpretation of periapical lesions has been addressed by numerous studies.[10] The periapical tissue responses can vary and assessment of a persistent radiolucency can be difficult unless a biopsy is performed. A radiolucency that persists following root canal treatment may be due to the root canal system still being infected, an extra-radicular infection, a periapical true cyst or a periapical scar.[11] Therefore it is prudent to submit the tissue postoperatively for the histopathological examination to derive at a final diagnosis.

The significance of submitting the specimen for histopathological examination lies in the fact that the chance of accurately interpreting the cystic formation on the basis of appearance of radiograph is poor. It provides an excellent opportunity to obtain complete information regarding the pathology and the microbiology of the lesion. It sharpens the diagnostic acumen related to periapical cyst, periapical granuloma or periapical abscess.[12]

The incidence of periapical abscess reported in the present study is 6.67%, which is in contrary to the findings of Ramachandran Nair et al and Ricucci et al where it was found it to be 35% and 28% respectively.[1314]

The incidence of periapical granuloma ranges from 46% to 84% according to various studies done by the authors. In the current study, there is 66.66% incidence of granulomas. Our study is in accordance with the previous studies of Sommer et al, winstock et al, Pattersen et al, Celia et al.[1415] whereas findings are contrary to the study done by Bhaskar, Demenico Ricucci and Lalonde & Luebke et al where they found it to be 48%, 45% and 40% respectively.[131617] The large variation in the frequency of granuloma occurrence may be due to differences in methods of biopsy collection and histological criteria used for the diagnosis of periapical lesions or may be due to smaller sample size.[18]

Accumulated data in the review of cytokeratin patterns in the post formative reduced enamel epithelium and the cell rests of Serres and Malassez, indicated that the major keratins consistently found were 13, 14 and 19.[19] Gao et al in their immunohistochemical based study on periapical lesions mention that expression of CK-14 in periapical granulomas would suggest an early change towards periapical cyst formation. Further they stated that this expression subsequently was replaced by CK-13 and CK-4, suggesting epithelial change to form a cystic lining is associated with more clearly differentiated phenotype of stratified non-cornifying epithelium but one in which some simple epithelial keratins were co-expressed.[20] The findings of strong expression of CK-14 in five periapical granulomas with cystic potential supports the view of Gao et al. Thus it appears that such periapical granulomas are more potential than the conventional granulomas to develop into cyst.

In the current study three out of thirty cases (10%) were diagnosed as periapical cysts which is in the reported range of literature (6-84%).[21] The inclusion of such potential granulomas (5) along with the true periapical cysts (3) in the present study would increase the incidence of periapical cysts to 27% which is relatively high. In views of Gao et al,[20] Safi et al,[21] Langeland et al[5] factors like serial sectioning, characteristics of the population sample, microscopic interpretation of the specimen and adjunct employment of appropriate CK markers would influence the reporting of incidence rates of periapical cysts in periapical lesions.

Regarding the location of the periapical lesions, a study by Nobuharo and Del Rio found majority in the anterior maxilla (47.3%) followed by posterior maxilla, posterior mandible and anterior mandible (8.7%).[1522] In this study the findings are similar to the above authors i.e 90% in anterior maxilla and remaining in anterior mandible. One of the reasons for the higher incidence of cysts in maxilla is due to the greater quantity of epithelial debris in the maxilla.[16]

Some earlier studies have attempted to relate histological and radiographic findings in periapical lesions; some authors have stated that a preliminary clinical diagnosis can be made when a lesion is greater than 20 mm in diameter or has a cross-sectional area ≥ 200mm[11522] White et al related the size and type of the lesion, establishing that cysts tend to be larger than granulomas.[23] Mortenson et al stated that a lesion greater than 1.5 cm can be safely classified as cyst.[15]

In the present study an attempt was made to not only locate or depict the size of the lesion but also to diagnose and categorize them radiographically as periapical granuloma, cyst and abscess and then co-relate the findings with the histopathological diagnosis. The correlation was seen only in 30% of the cases. Although 75% of the teeth requiring endodontic treatment can be successfully treated conservatively the other 25% of the cases definitely require the histopathological examination for accurate and confirmative results thus suggesting that diagnosis cannot be made solely on radiographic examination and histopathological examination is mandatory for the confirmation of the diagnosis.

CONCLUSION

The radiographic diagnosis of periapical lesions remains inconclusive. Although histopathologic examination of periapical lesions gives true nature, the precise nature of certain lesions may be achieved with adjunct use of immunohistochemical markers.

Future studies involving cytokeratin like CK-14 and proliferation markers like Ki-67 in adjunct with radiography and extensive follow-up may give better insight in understanding such subsets of periapical granulomas.