PEDIATRIC DENTISTRY/Copynght © 1982 byThe American Academy of Pedodontics/Vol. 4, No. 3

Ameloblastic fibroma: a case report

Ronald A, Bell, DBS, MEdDavid L. Schaffner, DOS, MSDavid R. Myers, DBS, MS

AbstractThe clinical and histopathologic features of a case of

ameloblastic fibroma in a 9-year-old boy has beenpresented along with a review of the literature. Thetumor responded to conservative surgical treatmentand there was no recurrence one year postoperatively.Analysis of the literature suggests that the tumor mayhave a higher potential for recurrence than is generallyappreciated. In addition, the possibility of maturationaldifferentiation and/or malignant transformation shouldbe recognized. The importance of early and accuratediagnosis, prompt treatment, and long-term followup isemphasized.

J. he ameloblastic fibroma is an uncommon,benign, mixed odontogenic neoplasm. It is the leastdifferentiated of the odontogenic mixed tumors inthat the neoplastic elements do not characteristical-ly produce dentin or enamel matrix, the hallmark ofthe more differentiated tumors. Biologically, it isgenerally regarded as being less aggressive than theameloblastoma, a feature which must be consideredin the rational treatment and management of the pa-tient with this tumor.

Report of CaseA 9-year-old Caucasian male was seen in February,

1980, in the pedodontic clinic at the Medical Collegeof Georgia School of Bentistry for routine examina-tion. The parent's only concern relating to the child'sdentition was that there was "too much spacing andsticking out of front teeth."

Extraoral examination revealed a well-nourished,healthy child with no evidence of lymphadenopathyor facial asymmetry. Intraoral examination reveal-ed that the permanent incisors, permanent firstmolars, primary cuspids and primary molars werepresent. The alignment of the posterior mixed denti-tion was normal with the exception of a partiallyerupted lower left first permanent molar which wasdisplayed approximately 6-7 mm distal to thedeciduous second molar (Figure 1). The opposing leftmaxillary first permanent molar had supraeruptedabout 2 mm. The soft tissues surrounding thedisplaced tooth were normal except for slight in-flamation associated with the operculum. The patientindicated no history of symptoms associated with the

Figure 1. Initial clinicalpresentation of distallydisplaced mandibular leftfirst permanent molar.

lower left quadrant and there was no tenderness topalpation. No buccal or lingual cortical expansionwas noted.

Radiographic examination revealed a multilocular,radiolucent lesion close to the crest of the alveolarridge occupying the space between the first perma-nent molar and the second primary molar. The firstpermanent molar was displaced and tipped distally6-7 mm (Figure 2). An occlusal radiograph (Figure 3)indicated no erosion but possible slight expansion ofthe lingual cortical plate.

An incisional biopsy was performed using intra-venous meperidine hydrochloride and diazepam seda-tion in conjunction with local anesthesia. Amucoperiosteal flap was reflected facially from themandibular left cuspid area to the distal of the firstpermanent molar, revealing the firm, white lesionaltissue which had eroded through the cortical bonealong with the alveolar crest. Several fragments ofthis tissue were curetted and submitted for histo-pathologic evaluation. The flap was repositioned andsutured interproximally with 3-0 plain gut sutures.

Histologic sections (Figure 4) showed a soft tissuespecimen consisting of a benign neoplastic prolifera-tion of fibrous connective tissue with numerous smallislands and cords of epithelium dispersed throughoutthe specimen. The epithelial component generallyconsisted of a double layer of columnar cells. The im-mature connective tissue stroma was characterizedby a loose network of delicate collagen fibers inassociation with spindle- and stellate-shapedfibroblasts. Some of the epithelial islands were rimm-ed by a zone of connective tissue hyalinization. Thediagnosis was ameloblastic fibroma.

The patient was admitted to Eugene TalmadgeMemorial Hospital for surgical removal of the lesion

PEDIATRIC DENTISTRY: Volume 4, Number 3 251

Figure 2. Bitewing radiograph showing multilocularradiolucent lesion, distally displaced mandibular first per-manent molar, and supraeruption of the maxillary left firstpermanent molar.

under general anesthesia. The patient's family andmedical history, and review of systems wereunremarkable. Preoperative laboratory work, in-cluding CBC, SMA-6, urinalysis, and chest x-rayfilms were within normal limits.

A full thickness mucoperiosteal flap extendingfrom the retromolar pad to the left primary caninewas reflected allowing removal of the buccal plate inthe area of the tumor. On exposure it became evidentthat the lesion extended inferiorly and lingually inproximity to the roots of the second primary molar.The second primary molar was removed and thetumor, the bulk of which was situated just beneaththe lingual cortex, was cleanly enucleated. The bonewas smoothed with a bone file and the area vigorous-ly irrigated. The gingiva was repositioned with multi-ple 3-0 plain gut sutures. The recovery andpostoperative period were uneventful and the patientwas discharged the day following surgery. Thesurgical specimen was submitted for histo-pathologic examination and the diagnosis ofameloblastic fibroma was confirmed.

Figure 3. Occlusal radiograph on the left mandible show-ing lingual orientation of the lesion with no apparent cor-tical erosion.

Follow-up examinations have been made at three,six, and twelve months. At one year, the secondbicuspid had emerged into the oral cavity with noevidence of developmental defect and the first per-manent molar had migrated mesially approximately4-5 mm. Radiographically, significant regenerationof bone and no evidence of residual or recurrenttumor were noted (Figure 5). The patient will be main-tained on a regular six-month recall schedule.

DiscussionThe ameloblastic fibroma is an odontogenic tumor

found primarily in children and teenagers (Table 1)with no apparent sex or race predilection. The lesionmay occur in either jaw, although 80% of thereported cases have been in the mandible, usually inthe premolar-molar area. The tumor enlarges bygradual expansion and often exhibits an asymp-tomatic clinical course. Pain or swelling may be thepatient's initial complaint.15

Ameloblastic fibroma radiographically presents asa unilocular or multilocular radiolucency with a

Figure 4. Photomicropgraph of the biopsy specimenshowing numerous cords of odontogenic epithelium dispers-ed throughout an immature connective tissue stroma(Hematoxylin and Eosin, original magnification 100 x).

Figure 5. Twelve-month postoperative radiograph of theleft mandibular area showing no sign of tumor recurrence.Significant regeneration of bone, normal bicuspid eruption,and mesial movement of the first permanent molar arenoted.

252 AMELOBLASTIC FIBROMA: Bell, Schaffner, and Myers

smooth, well-defined periphery. 1,2.5 Associatedfeatures may include unerupted or displaced teeth,divergence of the roots of adjacent teeth, or expan-sion of the cortical plates.1-6

Histologically, the ameloblastic fibroma ischaracterized by the proliferation of odontogenicepithelium supported by a primitive mesenchymalconnective tissue stroma.1,2 The epithelium presentsas nests, buds, and cords of cuboidal or columnarcells which may develop a central portion resembl-ing stellate reticulum. The cell-rich mesenchymalcomponent closely resembles the dental papilla of thedeveloping tooth germ. The ameloblastic fibromacontains no calcified tissue elements.

Generally credited as demonstrating benignbehavior, the recommended treatment forameloblastic fibroma consists of curettage orenucleation. 16 A few recurrences have beendocumented by Gorlin et al.,3.4 Heringer2 Tanaka7

and Lysell and Sund.8 Trodahl,~ in a survey of 24 casesfrom the Armed Forces Institute of Pathology, in-dicated 10 patients required further surgical pro-cedures after the initial treatment, an apparent recur-rence rate of 43.5%. In most of these recurrent casesthe initial surgical procedure was "believed to havecompletely removed the tumor, and yet itrecurred. ’’5 Interestingly, 4 of the 10 cases recurredmore than two years after initial treatment; the ma-jority of other cases, in which evidence of recurrencewas reported, were not followed for that length oftime.

The possible pathogenesis of ameloblastic fibromahas been correlated with the events of normalodontogenesis.~,~,’° This maturational theory of mixedodontogenic tumor origin proposes that theameloblastic fibroma and ameloblastic fibro-odontoma are progressive phases in the developmentof odontomas. In support of this viewpoint,Trodahl~ and Carr et al.,1 have pointed out that somerecurrent lesions initially diagnosed as ameloblasticfibroma showed maturation toward ameloblasticfibro-odontoma or odontomao On the other hand, thefact that no histologic evidence of additional matura-tion has been observed in many other examples ofrecurrent ameloblastic fibroma provides support tothe theory that the ameloblastic fibroma is an in-dependent entity.7.~.1~,13

Further support for the maturational theory isderived from the observation that all these tumorsshow a similar distribution in the jaws and occur inthe same general patient age population. ".1~ A moredetailed analysis of patient data by Slootwig,~6

however, showed the mean age of occurrence for theameloblastic fibroma to be 14.6 years in contrast to8.1 years for the ameloblastic fibro-odontoma.

In view of this data, the maturational theory seemsunlikely in that the more differentiated tumor shouldnot occur at a younger age than the tumor fromwhich it is hypothetically derived. Slootwig’s dataalso showed significant differences in the distributionof these two tumors. His data does supoort the con-cept that the ameloblastic fibro-odontoma may repre-

Table 1. Ameloblasticfibroma: data s~ ofdocumented cases through1980.

Author Number Sex Age Average SiteRecurrencesof cases M F Range Age Max. Mand.

Gorlin et al.4 36*

Trod~~ 24**

Heringer6 19"**

Addi~onal Reports****T~aka et M.~ ILysell & Su_nd~ 2Nflsen & Ma~usson~° 2Reich~t & Zobl~s 1Rodney & Carrin~on~a ILewin-Epstein et al.~ 1Singh & Agarwal~ 1Hager et al.~6 1Edwards & Goubran~7 tPresent Case 1

Totals 91

20 15 1V~-39y 14y 8 26 2

I6 8 1½-41y 15y 3 21 10

9 10 Im-42y 15y 3 16 1

1 7y 7y 1 11 1 7-13y 10y 2 11 1 9-14y I1V~y 1 1 01 16y 16y 1 11 6y 6y 1 0

1 8y 8y 1 01 35y 35y 1 0

1 7y 7y 1 01 18y lSy 1 01 9y 9y 1 0

53 37 lm-42y 14y 19 70 1659% 41% 21% 79% 18%

*Gorlin et al.~ reported 10 of their own cases and 26 compiled from published reports.**Trodahl~ reported on a survey of cases from the Armed Forces Institute of Pathology.

***Heringer~ documented 19 cases not included in the tabulations of Gorlin et al.~ and Trodahl)****Additional reports include cases not previously tabulated in comprehensive reviews.

PEDIATRIC DENTISTRY: Volume 4, Number 3 253

sent an immature form of an odontoma, but theameloblastic fibroma probably arises as a separateodontogenic tumor. Additionally, the ameloblasticfibroma is appropriately designated as a neoplasmas it has the potential for unlimited growth, recur-rence, and malignant transformation. This is indistinction to the odontoma which lacks these prop-erties and may be, more appropriately considered ahamartoma.

Of concern is the possibility of malignant transfor-mation of the ameloblastic fibroma into ameloblasticfibrosarcoma.l,.,.~8 The ameloblastic fibrosarcoma is a

rare malignant tumor of clusters and strands ofbenign epithelial components within a cell-rich mesen-chymal component exhibiting the cytologic featuresof a fibrosarcoma.l,17,~8.~9 Leider et al.20 and Goldstein etal. 2~ documented recurrent ameloblastic fibromas thathad transformed histologically into ameloblasticfibrosarcoma. These tumors were characterized byprogressive overgrowth and increased cellularity ofthe malignant mesenchymal component, leaving onlya few remnants of odontogenic epithelium.

In a review of fibrosarcomas of bone, Dahlin andIvins22 reported that 2 of 13 fibrosarcomas of the man-dible occurred at sites of previously diagnosedameloblastic fibroraa. In their review of the literature,Howell and Burkes ~’ identified 22 cases ofameloblastic fibrosarcoma and 89 cases ofameloblastic fibroma and fibro-odontoma. They sug-gest that although this high ratio of malignant le-sions may in part be artefactual due to the greaterlikelihood that a sarcoma will be reported, the malig-nant potential of ameloblastic fibroma may besomewhat higher than is generally appreciated. Theyconcluded, however, that the use of radical surgicalprocedures in the treatment of ameloblastic fibromais still not justified, although careful microscopicreview of the histopathology and a prolonged periodof followup is mandatory.

Summary

A case of ameloblastic fibroma of the posteriormandible in a 9-year-old boy has been presented. Theclinical and histological aspects of the case are typicalof ameloblastic fibroma, as is the lack of recurrenceduring the initial 12-month postoperative periodfollowing conservative surgical treatment. Given thequestions and concerns in the literature with regardto recurrence rate, possibility of maturational differ-tiation, and transformation into fibrosarcoma, the im-portance of early and accurate diagnosis, prompttreatment, and long-term followup must beemphasized.

Dr. Bell is associate professor and director of clinical pedodontics,Department of Pedodontics; Dr. Schaffner is assistant professor,Department of Oral Pathology; and Dr. Myers is professor and

chairman, Department of Pedodontics, School of Dentistry, MedicalCollege of Georgia, Augusta, GA 30912. Requests for reprintsshould be sent to Dr. Bell.

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254 AMELOBDkSTIC FIBROMA: Bell, Schaffner, and Myers