Recurrence rates of intraosseous ameloblastomas of the jaws: A systematic review of conservative versus aggressive treatment approaches and meta-analysis of non-randomized studies
Introduction
Ameloblasotmas appear in three main histologic types, solid or multicystic, unicystic and peripheral according to the 2005 WHO histological classification of odontogenic tumour (World Health Organization).
In the jaws clinicians encounter mostly cystic or unicystic and the more aggressive solid or multicystic ameloblastomas which are described as aggressively benign with problematic recurrences. Although metastasis of ameloblastomas is rare (Eckardt et al., 2009), there are several reports of metastasis to the lungs (Luo et al., 2012, Lin et al., 2014), cervical lymph nodes (Jayaraj et al., 2013), brain and bone (Zwahlen and Gratz, 2002) which highlights the potential aggressiveness and the complications that ameloblastomas can cause.
Peripheral ameloblastoma also known as extraosseoous ameloblastoma is mostly found in the retromolar aspect of the mandible. Peripheral ameloblastoma has a different biology compared to cystic and solid ameloblastoma. Peripheral ameloblastoma arises from either extraosseous remnants of dental lamina or the basal cell layer of surface epithelium (Buchner and Sciubba, 1987). Peripheral ameloblastoma represents only 1% of all ameloblastomas (Vanoven et al., 2008). In addition, peripheral ameloblastoma rarely show radiologic evidence of bone involvement and their differential diagnosis includes epulis, benign tumor, papilloma and pyogenic granuloma (Philipsen et al., 2001).
Ameloblastomas in the jaws present as cystic or unicystic versus solid or multicystic ameloblastomas, with most common being the latter. According to Carlson and Marx (Carlson and Marx, 2006) and Hong and associates (Hong et al., 2007) treatment and prognosis of ameloblastoma is heavily influenced by its histological classification. A systematic review and meta-analysis on the recurrence rates of unicystic ameloblastomas conducted by Lau and co-workers (Lau and Samman, 2006) showed the existence of weak only evidence of the superiority of jaw resection compared to other treatment forms. Pogrel & Montes (Pogrel and Montes, 2009) in their review consider only enucleation plus adjunctive treatments such as cryotherapy or use of Carnoy's solution as alternatives to resection and that as preferable only in selected cases of the unicystic variant. A recent attempt to explore the optimal treatment for unicystic ameloblastomas in children suggests that the luminal or cystic type is less aggressive and responds well to conservative treatment whereas plexiform and mural types may not (Seintou et al., 2014). On the other hand and in reference to solid or multicystic ameloblastomas it has been argued that jaw resection is highly curative and the treatment of choice for this type of ameloblastomas (Carlson and Marx, 2006). Sauk and co-workers give a new perspective on the management of ameloblastomas suggesting that research focusing on the pathogenetic mechanisms of the lesion may have a benefit to the end of a non-invasive therapy (Sauk et al., 2010). As a rule, clinicians have to consider in their treatment plan radiographic characteristics whereas the aggressiveness of the tumor could be evaluated only after its histological examination if not after the operation. From a descriptive epidemiology point of view, this is burdened by the fact that the histological characteristics of the tumor mentioned before and established by WHO are not used correctly at all times.
The aim of the present review was to summarize the recurrence rates of unicystic and solid or multicystic ameloblastomas and assess the effectiveness of radical and conservative treatment approaches on both variants.
Section snippets
Protocol and eligibility criteria
The present systematic review is conducted and reported according to the Cochrane Handbook (Higgins and Green, 2011) and the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) statement (Moher et al., 2009) and its extension for abstracts (Beller et al., 2013), respectively. Since no randomized controlled trials involving ameloblastomas were identified in the preliminary literature search, a systematic review of both randomized and non-randomized studies was planned.
Study selection and characteristics
A total of 1455 hits were retrieved by our search of electronic databases. Within the selected studies for this review the authors identified only two study types which were case-series and retrospective cohort studies. The number of identified studies and the selection process is illustrated in Fig. 1. Publication years of the included studies varied from 1977 to 2007. In total seventeen emails were sent by the authors requesting full-text copies of articles to which 4 groups or primary
Discussion
The summary recurrence rates showed fewer recurrences after radical treatment approach both in unicystic and solid or multicystic ameloblastomas over an average follow-up period of 5 years. (Fig. 1, Fig. 2). The calculated risk of recurrence after radical compared to conservative treatment approach in solid or multicystic ameloblastomas was lower (Fig. 4). The risk of recurrence comparing the two treatment approaches in cases of unicystic ameloblastoma could not be calculated. These findings
Conclusion
While the authors truly believe that solid ameloblastomas are best treated by resection rather than by so called conservative treatments, the current literature is replete with studies containing inadequate follow-up periods and does not clearly support this conclusion. Based on the existing evidence weak, at best, clinical recommendations can be made for the treatment of ameloblastoma patients. The authors conclude that the available evidence may suggest that smaller lesions could be managed
Funding
The present study was funded by an EVO grant from the Oulu University Hospital Pohjois-Pohjanmaan Sairaanhoitopiiri.
Financial disclosure
None.
Conflict of interest
None.
Acknowledgments
The authors thank Professor Jouko Miettunen from the Department of Psychiatry, Institute of Clinical Medicine, University of Oulu for providing his valuable comments.
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