Biologic Behavior of Ameloblastoma

Role of HIF-1α in Ameloblastoma: A Systematic Review

Hypoxia-inducible factor-1α is a transcriptional protein that has been extensively researched in human cancers whose overexpression is found to be associated with unfavorable prognosis. Contemporary studies have proved its vital role in ameloblastoma by correlating its expression with the aggressiveness of the tumor. Therefore, an attempt was made to explore its significance in the malignant transformation and prognosis of ameloblastoma. The present systematic review aimed to understand the impact of HIF-1α in AMB which might lead to favorable outcomes in the treatment. An electronic search was carried out using PubMed, Scopus, Google scholar, Cochrane library, and EMBASE databases. Original articles from all languages involving HIF-1α in AMB were scrutinized by two independent authors. Data were compiled and tabulated in Microsoft Excel and the Risk of bias was analyzed using the JBI tool. Twelve eligible articles were included for the quantitative analysis comprising 305 cases of AMB in which HIF-1α expression was studied for various characteristics like pattern, intensity, and site of immunoexpression which were found to be increased with an increase in the aggressiveness of AMB. It was concluded that HIF-1α is proven to have a crucial role in the progression and aggressiveness of AMB. Extended research regarding the crucial role of HIF-1α in the initiation of tumors and therapies aiming at HIF-1α in AMB cases might show promising outcomes in the future.

[Treatment features of odontogenic cystic formations of the mandible using cystotomy]

AIM

The aim of the study was to improve the types of surgical intervention when performing biopsy of large-sized cystic formations of the lower jaw by cystotomy.

MATERIAL AND METHODS

44 patients were examined and surgeries were performed: 12 patients with ameloblastoma, 14 - with keratoxystone tumor, 18 - with dentigerous cyst. All patients had a retained tooth in the cyst cavity.

RESULTS

For histological verification of cystic formations of large sized it is necessary to perform cystotomy-typed biopsy with bone tissue and shell fragment collection, using epithelialized flap method.

CONCLUSION

Cystotomy-typed biopsy using the method of epithelialized flap can significantly reduce the rehabilitation period and allows to decide on the choice of further method of surgical treatment.

Orbital invasion of ameloblastoma: A systematic review apropos of a rare entity

Purpose

Ameloblastoma is a non-encapsulated and slow-growing tumor with high recurrence rate. Orbital involvement by this neoplasm is an extremely rare entity. In this study, we present a systematic review on this situation along with clinical and paraclinical features of a case.

Methods

An electronic search was conducted on major medical sources. Data of the cases in the literature in addition to our own case were extracted, summarized, and statistically analyzed.

Results

A total of 36 other cases from 20 relevant studies were also reviewed. Review topics included epidemiology, clinical presentation, pathologic features, differential diagnosis, imaging, treatment, and prognosis. We provided a five-year history of a 50-year-old man with orbital/skull base invasion of plexiform maxillary ameloblastoma.

Conclusions

Maxillary ameloblastoma is a locally aggressive neoplasm, and physicians must be alert to the biologic behavior of this tumor to detect any invasion to critical structures such as orbit and cranium. Orbital ameloblastoma causes significant morbidity and mortality. We advocate meticulous patient follow-up with regular clinical examinations and paraclinical work-up for timely detection of any invasion or recurrence. The best must be done to avoid extensions by aggressive removal of maxillary ameloblastoma.

Molecular concepts in the pathogenesis of ameloblastoma: implications for therapeutics

Ameloblastoma is a benign odontogenic neoplasm that may exhibit aggressive biological behavior as evidenced by its rapid growth and significance recurrence rates following initial surgical resection. Currently, the only therapy for ameloblastoma is surgical, and adjunctive treatment modalities are needed to mitigate tumor growth and to reduce the need for extensive and disfiguring surgeries. Many studies have identified markers expressed by ameloblastoma and these lend insight to our understanding of tumor progression. This review provides a summary of the specific molecular pathways implicated in tumor pathogenesis, including those involved in bone remodeling, apoptosis, cell signaling, and tumor suppression. Based on these data, we identify several prognostic or therapeutic markers that have been used successfully in the treatment of other neoplastic processes that may also have diagnostic and prognostic utility for ameloblastoma. Thus, it is important to determine which markers hold the greatest promise for clinical management of this benign neoplasm in order to improve treatment options, particularly in patients with aggressive forms of ameloblastoma.

Plexiform ameloblastoma

The ameloblastoma is a benign but aggressive neoplasm of odontogenic origin. However, no enamel or hard tissue is formed by the tumor cells. Ameloblastomas are infamous for their invasive growth and their tendency to recur. Robinson (1937) as a benign tumor that is ‘usually unicentric, nonfunctional, intermittent in growth, anatomically benign and clinically persistent.’ They may occur at any age, even though nearly half of the tumors do occur between the ages of 20 and 40 years. This is the most common neoplasm affecting the jaws, yet only accounts for 1% of all tumors of the maxilla and mandible and 11% of all odontogenic tumors.

This report presents a case of ameloblastoma involving entire ramus and part of body of mandible with resorption of the mesial and distal root apices of second molar and distal root of mandibular first molar. The lesion extending till the base of mandible surrounding the crown of the unerupted third molar resembling the dentigerous cyst. This was surgically resected followed by harvesting the contralateral sixth costochondral rib graft.

How to cite this article: Celur S, Babu KS. Plexiform Ameloblastoma. Int J Clin Pediatr Dent 2012;5(1):78-83.

Intraosseous ameloblastoma with a prominent extraosseous component: pitfalls in diagnosis

For many years, gingival tumors of what appear to be peripherally located intraosseous ameloblastoma (IA) arising from the alveolar bone surface have often been confused with peripheral ameloblastoma (PA) causing resorption of the underlying bone. We analyzed a series of five cases of ameloblastoma that demonstrated a combined PA and IA architecture. The tumor commonly involved the anterior-premolar area, mostly in the maxilla and mainly in middle-aged men. The clinical presentation was an exophytic gingival mass inferior to which was a small bone defect. The predominant extraosseous component showed a papillary gross surface, reflecting the histologic proof of fusion between the submucosal tumor and the surface epithelium. In addition to the PA-like growth pattern, common to all was the presence of neoplastic destruction of the alveolar process, corresponding to an associated radiolucent lesion. This restrained component was acceptable as IA. In two cases, recurrence was observed deep in the alveolar bone with no involvement of the gingiva. These tumors appear to be IA that arose from the marginal alveolar bone and grew preferentially in the gingiva, forming a PA-like appearance. From diagnostic, therapeutic and prognostic points of view, this type of IA should not be confused with PA.

Tumor cell proliferation and microsatellite alterations in human ameloblastoma

Ameloblastoma is the most common odontogenic tumor. It can exhibit a variety of histological patterns, a great infiltrative potential and a high recurrence rate. Mutations in microsatellite sequences are a hallmark of neoplastic transformation but little is known about their role in ameloblastoma development. In this study DNA was extracted from laser-microdissected samples of 24 ameloblastomas and was analyzed for the status of 22 microsatellite loci. The occurrence and the pattern of microsatellite alterations, in form of loss or length variation, was evaluated and correlated with the Ki67 labeling index and with other clinicopathologic parameters. The prognostic significance of these alterations was also evaluated. High Ki67 expression was significantly associated with a shorter disease-free survival (p=0.003 by log-rank test). Alterations of at least one of the selected loci was observed in all (100%) the ameloblastomas analyzed with a mean of 4 altered microsatellites for each tumor. The microsatellites most frequently altered were D9S747 and D11S488 (42%). All the other loci analyzed were altered in less than 40% of cases and some of them (D3S1312, D3S1300, IFNA, D9S164, D13S176 and TP53) did not show alterations in any of the ameloblastomas analyzed. No relationship was observed between the occurrence of microsatellite alterations and other parameters, such as patients age and gender, tumor size, localization and histotype. The occurrence of microsatellite alterations was more frequent in tumors displaying a high Ki67 labeling index (p=0.03) and in a univariate analysis was predictor of an increased risk of disease recurrence (p=0.039 by log-rank test). These findings demonstrate that microsatellite alterations are frequent event in ameloblastomas. They also suggest that evaluation of tumor cells proliferative activity and microsatellite alterations may be helpful to stratify ameloblastomas prognostically and to predict the clinical behavior of these tumors.

Ameloblastic carcinoma: An analysis of 14 cases

OBJECTIVES

To present the classifications of malignant ameloblastomas, provide histopathologic guidelines for the diagnosis of ameloblastic carcinoma, and discuss treatment and long-term follow-up.

STUDY DESIGN

Fourteen archival specimens of ameloblastic carcinoma with detailed treatment and follow-up documentation were identified by the authors.

RESULTS

Traditional methods of microscopic observation form the basis for diagnosis. Histopathologic features of ameloblastic carcinoma include lack of differentiation, hypercellularity, high mitotic index, vascular invasion, and neural invasion.

CONCLUSION

The long-term follow-up findings in this study support the concept that aggressive surgical intervention provides the best chance for survival. Patients treated otherwise had recurrence. The patients with the highest number of recurrences did not survive the disease.

Odontogenic tumours, a collaborative retrospective study of 75 cases covering more than 25 years from Estonia

INTRODUCTION

The aim of the present collaborative study was to analyse retrospectively the character of odontogenic tumours in Estonia, involving the entire Estonian population (1.4 million), and to compare their prevalence with the figures presented in similar reports from other countries.

MATERIAL AND METHODS

All material for the retrospective study was retrieved from the files of the Departments of Maxillofacial Surgery in Tartu and Tallinn, Estonia, where all in/out-patients are treated from the whole country. The final diagnosis in each case of odontogenic tumour was based on the 1992 WHO histological criteria.

RESULTS

A total of 75 odontogenic tumours was found, 74 (98.6%) of which were benign, and 1 (1.3%) was malignant. The frequency of odontogenic tumours in this study was the lowest ever reported. The most common tumours were odontoma (34.3%), followed by ameloblastoma with different subtypes (25.3%), ameloblastic fibroma (16%), odontogenic myxoma (12%) and benign cementoblastoma (8%).

CONCLUSION

Odontogenic tumours are relatively rare in Estonia compared with the data from other countries.

Ameloblastoma in children

PURPOSE

The purpose of this report was 1) to report the experience of the University of Maryland, Department of Oral and Maxillofacial Surgery (OMS Department) in the treatment of ameloblastoma in children and 2) to review the world literature on the treatment of ameloblastoma in children from 1970 to 2001.

METHODS AND MATERIALS

This study first reviews the experience of the OMS Department of the University of Maryland with ameloblastomas in children and then reviews the literature on this subject. The first part of the study was undertaken by a retrospective chart review of all patients with a diagnosis of ameloblastoma in the OMS Department between May 1991 and December 1999. The literature on ameloblastoma in Western societies and Africa was separately reviewed from 1970 through 2001. Reports earlier than 1970 were not reviewed, as the histologic diagnosis of ameloblastoma was not well defined before that period.

RESULTS

In the Maryland series, 11 patients under the age of 20 years with ameloblastoma were treated. Eight patients were seen primarily, and 3 presented with recurrent lesions. The average age was 15.5 years; 5 of 11 patients were black, and 9 of 11 tumors were unicystic ameloblastomas. The literature review showed 85 children in the Western reports and 77 reported from Africa. The average ages were 14.3 and 14.7 years, respectively, but unicystic ameloblastomas accounted for 76.5% of the Western and only 19.5% of the African children, with an increased frequency of occurrence in the mandibular symphisis in African (44.2%) versus Western (5.8%) patients. Analysis of recurrence after enucleation of unicystic ameloblastomas in 20 children followed at least 5 years or until recurrence showed a recurrence of 40%.

CONCLUSIONS

Ameloblastomas in children differ from adults, with a higher percentage of unicystic tumors. African children appear to resemble the adult pattern. Although enucleation has been claimed to give acceptable recurrence rates in unicystic ameloblastoma, there are no large series with long follow-up in children. The histologic pattern that exhibits mural invasion in unicystic ameloblastoma suggests that more aggressive surgery is necessary.

Use of calretinin in the differential diagnosis of unicystic ameloblastomas

AIMS

Calretinin, a 29-kDa calcium-binding protein is expressed widely in normal human tissues and tumours including both unicystic and solid and multicystic ameloblastomas. The histological distinction between unicystic ameloblastomas and certain non-neoplastic odontogenic cysts can be problematic. The objective of this study was to determine whether calretinin was expressed in the lining epithelium of odontogenic keratocysts, residual and dentigerous cysts and to determine whether this calcium-binding protein could be used to distinguish these cysts from the unicystic ameloblastoma.

METHODS AND RESULTS

The lining epithelium in 22 cases of odontogenic keratocyst, 26 cases of residual cyst and 20 cases of dentigerous cyst were examined for the expression of calretinin. No positive epithelial staining was observed in any of these cystic lesions. In comparison, however, 81.5% of cases of unicystic ameloblastoma showed a coarse dark brown staining of the more superficial epithelial cell layers. Scattered positive stromal and epithelial cells were present; these were interpreted as mast cells.

CONCLUSIONS

Calretinin appears to be a specific immunohistochemical marker for neoplastic ameloblastic epithelium and we suggest that it may be an important diagnostic aid in the differential diagnosis of cystic odontogenic lesions and ameloblastic tumours.

Effect of preservation of the inferior and posterior borders on recurrence of ameloblastomas of the mandible

OBJECTIVE

The purpose of this study was to evaluate the experience and results of using a rational radical conservative approach in the surgical treatment of mandibular ameloblastomas.

STUDY DESIGN

A retrospective analysis of every patient with an ameloblastoma of the mandible treated in the Department of Oral Medicine and Oral Surgery at the Jordan University of Science and Technology between 1989 and 1999 was conducted. All were operated on by the author, who used a uniform surgical protocol in every case. All soft tissues in contact or overlying the lesion and a wide margin of cancellous bone related to the tumor were destroyed. The compact bone comprising the lower border of the mandible and the posterior border of the ascending ramus together with the nutrient periosteum attached to them were preserved, thus maintaining the continuity of the mandible and the facial contours. When teeth, soft tissues, or both were involved, they were destroyed. All patients were reviewed annually for a follow-up period of 3 to 10 years (mean, 6.5 years) by the same clinician.

RESULTS

All ameloblastomas were located in the mandible; 21 were in the angle/molar region and the ascending ramus, and 2 cases were in the anterior region. There was no clinical or radiographic evidence of recurrence observed during the follow-up period.

CONCLUSION

Ameloblastoma has a high rate of local recurrence if it is not adequately removed. The findings of this study to date suggest that the technique of rational radical conservative resection may have a place in the treatment of ameloblastoma of the mandible and is worthy of further trial.

Ameloblastoma--a diagnostic problem

A 50-year-old female was referred by her dental practitioner. She had a periapical radiolucency associated with the lower right second premolar tooth. The tooth was root treated and subsequently apicected. Tissue curetted at the time of surgery was shown to be a solid ameloblastoma which was managed initially by marginal excision. Histopathological examination of the resection specimen demonstrated tumour at the inferior margin. A segmental resection of the mandible with an immediate reconstruction using a free tissue transfer of the iliac crest was therefore performed. The case shows the need for vigilance in dealing with periapical pathology and underlines the importance of sending all tissue specimens for histopathological analysis.

Clinical features and management of oral and maxillofacial tumors in children

OBJECTIVE

To clarify the characteristics of oral and maxillofacial tumors in children, we carried out a clinical study of such tumors and reviewed the relevant procedures for treatment. Study design. Medical records of 105 patients less than 15 years of age who were treated for oral and maxillofacial tumors during the 20 years between 1976 and 1997 were retrieved and analyzed.

RESULTS

Of the 105 cases, 102 (97.1%) involved tumors that were benign; only 3 patients (2.9%) had tumors that were malignant. With regard to benign soft tissue tumor, the most common type was hemangioma (25/69; 36.2%), the second most common type was papilloma (19/69; 27.5%), and the most common site was the tongue. With regard to bone tumor, the most common type was odontoma (14/33; 42.4%), the second most common type was ameloblastoma (11/33; 33.3%), and the most common site was the mandible. Most of the odontogenic tumors (25/28; 89.3%) developed in patients more than 6 years of age; these tumors may develop after dental crown formation. In each case of benign soft tissue tumor, resection was performed; 4 of these tumors (2 hemangiomas, 1 lymphangioma, and 1 papilloma) recurred, but after re-resection recurrence has not been found for more than 4 years. In the cases of benign jawbone tumor, resection and enucleation were the procedures principally performed; 3 ameloblastomas recurred after enucleation, but after relatively wide resection for these recurrent tumors there has been no recurrence for more than 17 years. With regard to the ameloblastomas, enucleation with preservation of the periosteum was effective and bone regeneration occurred rapidly.

CONCLUSIONS

Most oral and maxillofacial tumors in children are benign. In any case of such benign tumor, including ameloblastoma, minimal surgical treatment should be the procedure of first choice.

Unicystic ameloblastoma. A review of 193 cases from the literature

Based on a world-wide literature survey of 193 published cases of unicystic ameloblastomas (UA), data have been produced allowing the presentation of a revised concept of this much debated lesion. UA is a variant of the solid or multicystic ameloblastoma. Radiographically, the unilocular pattern is more common that the multilocular, especially in cases associated with tooth impaction. However, it is stressed that although the lesion is pathomorphologically unicystic, it will far from always produce a unilocular radiolucency. The mean age at the time of diagnosis of UA is closely related to an association with an impacted tooth. Almost 20 years separate the mean age of the 'dentigerous' variant from the 'non-dentigerous' (16.5 years versus 35.2 years) The male:female ratio for the 'dentigerous' type is 1.5:1, but for the 'non-dentigerous' type it is reversed (1:1.8). Location favours greatly the mandible (mandible to maxilla = 3 to 13:1). Between 50 and 80% of cases are associated with tooth impaction, the mandibular third molar being most often involved. The 'dentigerous' type occurs on average 8 years earlier than the 'non-dentigerious' variant. The mean age for unilocular, impaction-associated UAs is 22 years, whereas the mean age for the multilocular lesion unrelated to an impacted tooth is 33 years. Histologically, the minimum criterion for diagnosing a lesion as UA is the demonstration of a single cystic sac lined by odontogenic (ameloblastomatous) epithelium often seen only in focal areas. This simple type of UA (according to the authors' modification of the classification by Ackermann et al. (Journal of Oral Pathology 1988; 17:541-546)), is one of four UA subtypes, the others being (1) simple with intralumenal proliferations; (2) simple with both intralumenal and intramural proliferations; and (3) simple with intramural proliferations only. All four subtypes occur in both the 'dentigerous' and 'non-dentigerous' variants. The simple subtype with and without intralumenal proliferations may be treated conservatively (enucleation), whereas subtypes showing intramural growths must be treated radically, i.e. as a solid or multicystic ameloblastoma. Finally, the authors disclose areas and issues pertaining to UA that still need to be addressed.

Some current concepts on the pathology of ameloblastomas

This article describes some fundamental concepts and new developments in the pathologic characteristics of ameloblastoma. The former include (1) the necessity of separating ameloblastomas into three clinical types, namely the solid or multicystic (the classic intraosseous ameloblastoma), the unicystic, and peripheral varieties; (2) the importance of the tumor's location in the jaws; and (3) the manner in which cancellous and compact bone of the jaws affect the spread of ameloblastomas. New developments discussed include the desmoplastic ameloblastoma, the clear cell ameloblastoma, the recognition of the so-called acanthomatous epulis in dogs as a fairly common spontaneous animal model of ameloblastoma, and some work concerning therapeutic irradiation of ameloblastomas. Additional topics include the problems involved in the early microscopic diagnosis of ameloblastoma and of ameloblastic carcinoma and our lack of knowledge concerning the cause of ameloblastomas.