|Year : 2009 | Volume
| Issue : 1 | Page : 70-74
Unicystic plexiform ameloblastoma: An insight for pediatric dentists
C Yavagal, R Anegundi, S Shetty
Department of Pediatric Dentistry, SDM College of Dental Sciences and Hospital, Dharwad, India
Department of Pediatric Dentistry, S.D.M. College of Dental Sciences, Dharwad - 580 009, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Ameloblastomas have been categorized broadly into three biologic variants: cystic (unicystic), solid, and peripheral. The term plexiform unicystic ameloblastoma refers to a pattern of epithelial proliferation that has been described in cystic lesions of the jaws. Although the histology suggests that cystic ameloblastomas follow a biologically low-grade course, recent evidence suggests that they may often behave clinically as biologically aggressive tumors. This is supported by the high incidence of cortical perforation, tooth resorption, lesion size, bony destruction, and a high rate of recurrence after simple enucleation. This article tries to provide an insight for pediatric dentists regarding this biologically distinct entity. A literature review on the topic has been added along with a case report highlighting the state-of-the-art approach and management of such ameloblastomas, in pediatric patients.
Keywords: Ameloblastoma in children, pediatric maxillofacial lesions, unicystic plexoform lesions
|How to cite this article:|
Yavagal C, Anegundi R, Shetty S. Unicystic plexiform ameloblastoma: An insight for pediatric dentists. J Indian Soc Pedod Prev Dent 2009;27:70-4
|How to cite this URL:|
Yavagal C, Anegundi R, Shetty S. Unicystic plexiform ameloblastoma: An insight for pediatric dentists. J Indian Soc Pedod Prev Dent [serial online] 2009 [cited 2020 Feb 28];27:70-4. Available from: http://www.jisppd.com/text.asp?2009/27/1/70/50824
| Introduction|| |
Ameloblastomas have been categorized broadly into three biologic variants: cystic (unicystic), solid, and peripheral. The literature indicates that the cystic variant is biologically less aggressive and has a better response to enucleation or curettage than the solid ameloblastoma.  In six studies on cystic ameloblastomas, the overall recurrence rate for all cases was 15%, with some evidence to suggest that the mural histological subtype had a greater recurrence rate than the others. 
The term plexiform unicystic ameloblastoma refers to a pattern of epithelial proliferation that has been described in cystic lesions of the jaws. It does not exhibit the histological criteria for ameloblastoma published by Vickers and Gorlin,  and has therefore been considered by some pathologists to be a hyperplastic epithelial proliferation rather than an ameloblastoma. In 1977, Robinson and Martinez  first contributed the term 'unicystic ameloblastoma'. They purported the unicystic variant as a less aggressive variant of ameloblastoma and suggested simple enucleation as the treatment.
The histology of cystic ameloblastomas is deceptively bland. Basal palisades and intercellular edema are features that characterize this tumor. Recurrence of a cystic jaw lesion with this simple pattern should be regarded as a possible cystic ameloblastoma. The finding of positively stained Ki-67 cells in dentigerous cysts (6.6%), cystic ameloblastomas (4.3%), and solid ameloblastomas (2.8%) is contrary to what one might expect, suggesting that the biological aggressiveness of cystic ameloblastomas is less likely related to increased cellular proliferation than to other factors. Although the histology suggests that cystic ameloblastomas follow a biologically low-grade course, they may often behave clinically as biologically aggressive tumors. This is supported by the high incidence of cortical perforation, tooth resorption, lesion size, bony destruction, and a high rate of recurrence after simple enucleation.
The pathogenesis of cystic ameloblastomas remains obscure. The reason why some ameloblastomas become completely cystic may be related to epithelial dysadhesion (e.g., defective demosomes) or, more likely, to the intrinsic production of proteinases (e.g, metalloproteinass, and serine proteinases); enzymes that normally degrade the central zone of the enamel organ after tooth development. 
Incidence and Predilection
Unicystic ameloblastoma has been reported to occur more often in a younger population (third decade) than its solid counterpart (fourth decade). 
Unicystic ameloblastomas have a marked predilection for the mandible. In fact, in Gardner and Corio's study of 46 examples of histological variants of unicystic ameloblastoma, referred to as plexiform unicystic ameloblastoma, not one occurred in the maxilla.  All unicystic ameloblastomas in the series reported, respectively, by Robinson and Martinez,  and by Eversole, Leider, and Sturb  occurred in the mandible.
Review of the literature
Ameloblastoma is uncommon in children. The most commonly quoted article regarding ameloblastoma is a review of 1,036 ameloblastomas, in which the average patient age is 38.9 years, with only 2.2% (19 of 858) under 10 years and 8.7% (75 of 858) between 10 and 19 years.  This report, however, was published in 1955, when adenoameloblastomas and ameloblastic fibromas were included in ameloblastomas and before the histological characteristics for ameloblastomas in cysts and been delineated. Kessler and Dominquez  described eight of 92 patients (8.7%) less than 16 years of age, whereas, Khan  found 38 of 311 ameloblastomas (12.2%) in patients younger than 19 years. Mehlisch et al ,  found 16 of 126 patients (12.6%) to be less than 20 years of age, but only one patient under the age of 10, and Sandler et al ,  found 15% of their 87 patients to be under 20 years of age and 3% to be under the age of 10.
A large series of Asian patients show a higher percentage of children with ameloblastoma to be younger that 20 years: 19 of 104 Japanese patients (18.2%) ,) and 29 of 147 Thai patients (19.7%). 
| Case Report|| |
A 13-year-old girl was referred to the Department of Pediatric Dentistry, SDM College of Dental Sciences and Hospital, Dharwad, with a swelling in the left mandible [Figure 1]. The swelling was painful and had been slowly increasing in size for a year. On extra oral examination, the swelling was about 5 cm x 5 cm in size on the left mandible extending to about 4 cm from the symphisis region to 1 cm in front of the ear lobule, and supero-inferiorly it was 2 cm from the zygoma to 1 cm below the lower border of the mandible. The swelling was fluctuant in certain areas and hard in other areas. The swelling was tender to palpation and a mild temperature rise over the swelling was apparent. Intraorally, the swelling extended from the mesial surface of 34 to the distal aspect of 36 [Figure 2]. The orthopantomograph revealed a well-defined unicystic radiolucency from one periapical region of 35 and 36 to the inferior border of the mandible, involving the body ramus and coronoid process of the mandible on the involved side [Figure 3]. It was found that 37 was impacted and radiolucency was present around the crown portion of 37. Later FNAC (Fine Needle Aspiration Cytology) was performed [Figure 4]. The cytosmear showed numerous neutrophils, macrophages, and few desquamated epithelial cells in an eosinophilic background, and hence no conclusive evidence could be drawn from the same [Figure 5].
Therefore, an extensive enucleation of the said lesion along with sub-periosteal dissection was planned under general anesthesia. A CT scan was advised, to plan a meticulous approach [Figure 6]. A Modified Wards incision was placed using a No.15 B.P. blade, extending anteriorly up to the region of 35 [Figure 7]. After reflecting the mucoperiosteal flap, the expanded cortical plate was identified and separated from the mucoperiosteum. Subperiosted dissection was carried out beginning from the sound bone near the 35 region, posteriorly [Figure 8]. The mental nerve was identified and preserved. The cystic lining was separated from the inferior border of the mandible taking care not to injure the inferior alveolar nerve. The impacted tooth bud was delivered out with its cystic lining. The retracted cystic mass [Figure 9] was then sent for histopathological analysis. The section [Figure 8] showed a cystic epithelium with cuboidal to columnar peripheral cells and few loosely packed stellate cells. The epithelium showed plexiform in the luminal prolifery and subepithelial hyalinization. The odontoblastic rests were seen within the fibrous capsule. Based on these findings a diagnosis [Figure 10] of unicystic plexiform ameloblastoma was made.
| Discussion|| |
The unicystic ameloblastoma, a variant of ameloblastoma, first described by Robinson and Martinez in 1977,  is reported to have a less aggressive biologic behavior and lower recurrence rate than the classic solid or multicystic ameloblastoma. Although the unicystic ameloblastoma is a "cystic" appearing lesion on gross examination, subsequent microscopic examination shows the presence of an ameloblastoma within the cyst wall. Prior to the report by Robinson and Martinez, this variant had been referred to as a mural or intraluminal ameloblastoma.
There are various subtypes of unicystic ameloblastoma depending on the character and extent of ameloblastic proliferation within the cyst wall. Vickers and Gorlin, in 1970,  first described the features of the early ameloblastic change that occurs within the wall of a cyst. These include hyperchromatism of the nuclei in the basal cell layer of the epithelial lining, palisading and polarization of the basal cell nuclei away from the basement membrane, and cytoplasmic vacuolization of the basal cells. In 1988, Ackerman et al ,  suggested categorizing the unicystic ameloblastoma into the following variants:
Those in which the lining epithelium shows features of early ameloblastic transformation, as described by Vickers and Gorlin,  in some areas.
Those with intramural proliferation in which the neoplastic epithelium has extended into the connective tissue wall of the cyst.
| Conclusions|| |
This article tries to highlight some recent concepts about unicystic plexiform ameloblastomas in children, based on a case report, and also tries to emphasize the fact that recent insights into the biologic nature of these lesions seem to suggest that they could be more aggressive than previously thought. Hence reconsideration should be given to their treatment. It should not often be the case where the pediatric dentists or maxillofacial surgeons perform enucleation or excisional biopsy for a presumed dental cyst only to be informed later of the diagnosis of cystic ameloblastoma. Hence it is important to reiterate that, an accurate and timely diagnosis of the character and extent of a unicystic ameloblastoma (with a thorough microscopic examination of the entire specimen) can go a long way in the overall meticulous rehabilitation of the child.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
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