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October2009I MumbaiI VolumeIII I Issue10I Pages60 I Price:Rs.80

ISSNNO.Print-ISSN0974-39791SSNNO.Online-ISSN0974-4916

ital01 clinicaldentistry. ida.org. in

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Clinical Dentistry

PLEXIFORMUNICYSTICAMELOBLASTOMA- A CASEREPORTANDTHELITERATUREREVIEWAbstractII BriefBackgroundThe paper presents a less common case of plexiform unicysticameloblastoma, a review of its literature, diagnosis andmanagement.

II Materials and MethodsIntraoral examination, panoramic radiograph, CT scan andhistopathological examination led to the diagnosis of plexiformunicystic ameloblastoma, following which segmental resectionof the mandible was done.

II DiscussionDiscussion pertained to explaining the various types ofameloblastoma, their characteristics, the histologicallyacceptedcriteria, occurrence pattern and proliferation into cystic lumenand the treatment modalities.

II Summary and ConclusionsUnicystic ameloblastoma is an ameloblastoma developingwithin the lining, lumen, or wall of a cyst besides being aninvasive ameloblastoma that has a single cystic space ratherthan multicystic spaces. It usually occurs in patients around 18to 20 years of age with a strong predilection for the posteriormandible. Unicystic ameloblastoma is treated with segmentalresection and reconstruction with iliacgraft and reconstructiveplate.

II KeyWordsCyst,tumour, ameloblastoma, odontogenic

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II IntroductionThe Unicystic Ameloblastoma is less common thanthe common intraoseous ameloblastoma, but it isimportant because it has a better prognosis. It occurspredominantly in the second and third decades, i.e.,in younger people than the classical intraosseousameloblastoma. Almost all have occurred in the

posterior aspect of the mandible. This lesiongenerally appears radiographically as a dentigerouscyst, and if it is not too large, is enucleated on thatbasis. It is only when a pathologist examines such alesion that it is apparent that it is an ameloblastoma.However, the larger ones are examined by anincisional biopsy and present a real problem. In thesecases, the pathologist may suggest the diagnosisof unicystic ameloblastoma, based on the patient'sage, the radiographic appearance of the lesion, andits microscopic features, but he or she cannot becertain that the tumour has not breached the fibrous

wall of the cyst in other parts of the lesion. Oneneeds to examine the entire specimen to make thatevaluation.

IICase ReportA 31 year old male patient reported with complaintof pain and swelling on the right side of the face.He experienced dull and continuous pain since onemonth followed by swelling. When the patient firstvisited our hospital, observable swelling was foundin the right posterior region of the mandible causingexpansion of both lingual and buccal cortices. Onintraoral examination, mucosal inflammation wasobserved with obliteration of the mandibularvestibule

on the right side from first premolar till the retromolarregion. The right lower second molar was mobile. On

Fig.( I) Preoperative front view

palpation "egg shell crackling" was observed on fewareasof buccal vestibule.

Panoramic radiograph revealed a well definedradiolucency associated with impacted rightmandibular third molar extending anteriorly tillsecond premolar with resorption of the second andfirst molar roots. The mandibular canal deflected

downward due to the cystic enlargement. (T scanrevealed perforation of both buccal and lingualcortices. After the radiological examination, incisionalbiopsy was performed. The histopathologicalexamination suggested unicystic plexiformameloblastoma. It showed cystic lining with columnarbasal cells, nucleus palasiding with polarizationand hyperchromatism, cytoplasmic vacuolizationwith intercellular spacing. Strands of odontogenicepithelium were seen extending into the connectivetissue from the lining and producing plexiformpattern with stellate reticulum like tissue betweenthe strands.

Under the final diagnosis of plexiform unicysticameloblastoma, segmental resection of themandible from distal of right first premolar to distalof the impacted right third molar was performed. Thecortico-cancellous graft was harvested from rightanterior iliac crest and secured to the defect with

the help of stainless steel reconstruction plate. Thepostoperative healing was uneventful. In the follow-up period of 2 years, no evidence of recurrence wasobserved.

II DiscussionPlexiform pattern of epithelial proliferation,which does not exhibit the histologic criteria forameloblastoma published by Vickers and Gorlin,

Fig. (2) Intra oral view showing obliteration of the vestibule

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Fig. ( 3 ) Pre operative OPG

occurs in dentigerous cysts. Some pathologistshave diagnosed it as ameloblastoma yet othershave considered it to be epithelial hyperplasia.Gardner DGhas studied Sections of 19 cases and thelimited clinical information available. Histologicallycharacteristic ameloblastoma was found associatedwith this pattern in nine cases and one case,exhibitingonly this pattern, recurred. It is concluded that thepattern in question is in fact ameloblastoma and thatVickers and Gorlin's criteria, although valuable, aretoo rigid for the diagnosis of this plexiform patternof ameloblastoma in dentigerous cysts.There is needfor further study on the natural behaviour of thesetumours. However, enucleation with good follow-upexamination is probably sufficient for tumours thathave proliferated into the cystic lumen, but moreextensive surgery is indicated for those involvingtheperiphery ofthe fibrous connective tissue wall of thecyst.This pattern occurs primarilyduring the secondand third decades of life,generally in the mandible.The term plexiform unicystic ameloblastoma isproposed for this lesionto distinguish it from classicalplexiform ameloblastoma.!

The term, plexiform unicystic ameloblastoma,refers to a pattern of epithelial proliferation that hasbeen described in dentigerous cysts, primarily inpersons in the second and third decades of lifeandpredominantly in the posterior part of the mandible.Gardner and Corio's article provides the first studyon the biologic behaviour of these lesions. Of 28examples treated by enucleation/curettage, and forwhich adequate follow-up information was obtained,only three recurred. Their figure (10.7%) comparesvery favourably with the 55% to 90% recurrencerate quoted for ameloblastomas of all types thathave been treated by curettage and is similarto thatfound inother typesof unicysticameloblastoma.The

Fig. ( 4) Intra operative photo showing incision line marked

plexiformunicystic ameloblastoma isconcluded fromtheir study to be an undifferentiated histologicvariantof unicystic ameloblastoma and not a separate entity.Enucleation with long-term follow-up informationis adequate for tumours that have proliferated intothe lumen of the cyst, but more extensive surgery isrecommended for those that involve the peripheryof its fibrous connective wall. Their study has alsoshown that plexiform unicystic ameloblastomas arenot alwaysassociated with unerupted teeth, in whichcase they probably occur over a wider age range thanthose resemblingdentigerouscysts.2

Philipsen Hp, Reichart PA have published a paperbased on a world-wide literature survey of 193published cases of unicystic ameloblastomas (UA);data have been produced allowing the presentationof a revised concept of this much debatedlesion. UA is a variant of the solid or multicysticameloblastoma. Radiographically, the unilocularpattern is more common that the multilocular,especially in cases associated with tooth impaction.However, it is stressed that although the lesionis pathomorphologically unicystic, it will far fromalways produce a unilocular radiolucency.The meanage at the time of diagnosis of UAis closely relatedto an association with an impacted tooth. Almost20 yearsseparate the mean age of the 'dentigerous'variant from the 'non-dentigerous' (16.5years versus35.2years)The male:femaleratioforthe 'dentigerous'type is 1.5:1, but for the 'non-dentigerous' type it isreversed (1:1.8).Locationfavoursgreatly the mandible(mandible to maxilla = 3 to 13:1).Between 50 and80% of cases are associated with tooth impaction,the mandibular third molar being most ofteninvolved.The 'dentigerous' type occurs on average 8years earlier than the 'non-dentigerious' variant. Themean age for unilocular,impaction-associated UAsis

18 Clinical Dentistry, Mumbai . October 2009

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Fig.( 5 ) Excisedspecimen

22 years, whereas the mean age for the multilocularlesion unrelated to an impacted tooth is 33 years.Histologically, the minimum criterion for diagnosinga lesion as UA is the demonstration of a single cysticsac lined by odontogenic (ameloblastomatous)epithelium often seen only in focal areas.This simpletype of UA, according to the authors' modificationof the classification by Ackermann et a13,is one offour UA subtypes, the others being (1) simple withintralumenal proliferations; (2) simple with bothintralumenal and intramural proliferations; and (3)simple with intramural proliferations only. All foursubtypes occur in both the 'dentigerous' and 'non-dentigerous' variants. The simple subtype with andwithout intralumenal proliferations may be treatedconservatively (enucleation), whereas subtypesshowing intramural growths must be treated radically,Le.,as a solid or multicystic ameloblastoma. Finally,the authors disclose areas and issues pertaining toUA that still need to be addressed.4

The term plexiform unicystic ameloblastoma refersto a pattern of epithelial proliferation that has beendescribed in cystic lesions of the jaws. It has beenconsidered hyperplastic epithelium, rather thanameloblastoma, by some pathologists because itdoes not exhibit previously accepted histologiccriteria for ameloblastoma. Gardner and Corio's article

provides histologic evidence that plexiform unicysticameloblastoma is, in fact, a variant of conventionalunicystic amelobllstoma by reporting ten cases ofunicystic ameloblastoma that exhibit both patterns.Further evidence of the ameloblastomatous nature

of plexifqrm unicystic ameloblastomas is that theirbiologic behaviour, even when this pattern occursalone, is similar to that of conventional unicysticameloblastoma.s

Fig.( 6 ) Reconstruction of the defect with iliacgraftandreconstructive plate

Matsumoto, Mizoue and Seto have reported a tumourthat resembled previously reported uncommontumours histologically similar to ameloblastoma oradenomatoid odontogenic tumour (AOT), showingthe formation of hard tissue. They evaluated thehistological characteristics by reviewing the literature.The patient was a 19-year old male. The lesion waslocated from the canine to third molar in the rightmandible and was unicystic with a comparativelyclear demarcation. The tumour tissue was cysticoverall, showing multiple formations of small andlarge cysts. The tumour tissue resembled a variantform of plexiform ameloblastoma. Formation ofdentin and dentinoid was observed in the tumour

stroma, whereas formation of enamel was not

observed. Very few cases of a variant form ofameloblastoma that shows formation of dentinoid

have been reported, and the histological picture intheir study closely resembled previously reported"adenoid ameloblastoma with dentinoid':6

A case of an atypical odontogenic tumour withfeatures of unicystic plexiform ameloblastomaand odontoblastic differentiation with depositionof tubular dentin matrix is reported by Orlowski,Doyle and Salb. The significance of dentinogenesis,amelogenesis, and calcification in odontogenictumours is discussed in their article.7 Plexiform

unicystic ameloblastomas havea marked predilectionfor occurring in the posterior part of the mandible.Gardner, Morton and Worsham have presented thefirst report of sucha lesion in the maxilla.8

Navarro, Principi, Massucato and Sposto havepresented a case of a 17-year-oldWhite male

Clinical Dentistry, Mumbai . October 2009 19

Clinical Dentistry

-,

Fig.( 7) Post operative OPG after one year.

patient complaining of enlargement in the gingivalregion and the fundus of the left maxillary anteriorvestibular sulcus. The clinicopathological diagnosiswas plexiform unicystic ameloblastoma. With theirreport, the authors have illustrated the importanceand complexity of a differential diagnosis of lesionswith a cystic aspect in the anterior region of themaxilla, among them inflammatory radicular cysts,odontogenic keratocysts,adenomatoid odontogenicand unicystic ameloblastoma.9

Three histopathologic variants of unicysticameloblastoma have been described.lO In the first

type (luminal unicystic ameloblastoma), the tumourisconfined to luminal surface of cyst;while the lesionconsists of fibrous cyst wall, with a lining that consistspartially or totally of ameloblastic epithelium.

This demonstrates a basal layer of columnar orcuboidal cells with hyperchromatic nuclei thatshow reverse polarity and basilar cytoplasmicvacuolization. The overlying epithelial cells are looselycohesive and resemble stellate reticulum. The findingthus seems to be related to inflammatory edema.In the second microscopic variant (intraluminalunicystic ameloblastoma), one or more nodules ofameloblastoma project from cystic lining into lumenof cyst.These nodules may be relatively small or theylargely fill the cystic lumen. In some cases,nodulesof tumour that project into lumen demonstrate anedematous plexiform pattern that resemblesplexiformpattern seen in conventional ameloblastoma.These lesions are referred to as plexiform unicysticameloblastoma. In the third variant (mural unicysticameloblastoma), the fibrous wall of cyst is infiltratedby typical follicular or plexiform ameloblastoma.The extent and depth of ameloblastic proliferationmay vary considerably. With any presumed unicysticameloblastoma, multiple sections through manylevels of specimen are necessary to rule out thepossibility of mural invasion of tumour cell.ll

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Classification of ameloblastoma into solid or

multicystic, unicystic and peripheral types based onthe biological behavior hasgained recent recognition.Tie-J and Motoo have reviewed available English-language literature on unicystic ameloblastomasince its first description in 1977. A total numberof 182 cases was retrieved to evaluate various

clinical and pathological aspects of this variant. Thetumour tends to occur at a younger age (mean: 25.5years) and exhibits a low rate of recurrence (13.8%)following enucleation or curettage in comparisonto the conventional ameloblastoma. The variabilityof histological spectrum, diagnostic problems andchoice of treatment for this form of ameloblastoma

were also discussed in the light of recent researchinterest and progress.12

Most unicystic ameloblastomas are diagnosed bythe pathologist once it is completely enucleated.No further treatment is indicated, other thanradiographing the surgical site annually for a periodof ten years if it can be demonstrated microscopicallythat the ameloblastoma is confined to the epitheliallining or is an intraluminal nodule. If. however, theameloblastoma has invaded the cystic capsule, thesurgeon may consider the option of further surgerysuch as marginal resection to ensure that the tumourhas been completely removed. The overall recurrencerate of the unicystic ameloblastoma after enucleationis 10%to 15%.The rare unicystic ameloblastomas ofthe posterior maxilla should be treated by marginalresection because recurrences in that location can

involve the pterygomaxillary fossa and are thereforedangerous. Once the unicystic ameloblastoma hasbreached the fibrous connective tissue capsuleof the cyst, it becomes a classical intraosseousameloblastoma, and should be treated assuch.13

II ConclusionThe unicystic ameloblastoma is a less aggressiveneoplasm and occurs in younger patients. It usually

20 Clinical Dentistry, Mumbai . October 2009

Clinical Dentistry

occurs in patients around 18to 20 years of age with astrong predilection forthe posterior mandible. Almost90%ofcases areassociated withthe crown ofimpactedthird molar teeth with the radiographic presentationof a dentigerous cyst.Thistype of ameloblastoma canarisefrom a dentigerous cyst or de novo next to a cyst.The former is more commonly seen. In about 10%of cases, it can present as a unilocular radiolucencysimulating a residual cyst, periapical, primordial cystor Odontogenic keratocyst (OKC).Radiographically,it is unilocular and corticated radiolucency and, attimes, the margins are scalloped, simulating an OKC.

II References

1. Gardner DG. Plexiform uni<;:ystici ameloblastoma: A

diagnostic problem in dentigerous cysts. Cancer 1981Mar 15; 47(6):1358-63.

2. Gardner DG,Corio RL.Plexiform unicystic ameloblastoma.A variant of ameloblastoma with a low-recurrence rate

after enucleation. Cancer. 1984 Apr 15; 53(8):1730-5.

3. Ackermann GL, Altini M, Shear M. The unicystic

ameloblastoma: a clinicopathological study of 57 cases. JOral Pathol. 1988 Nov;17(9-1 0):541-6

4. Philipsen HP. Reichart PA. Unicystic ameloblastoma. Areview of 193 cases from the literature. Oral Oncol. 1998

Sep;34(5):317-25.

5. Gardner DG, Corio RL. The relationship of plexiform

unicystic ameloblastomatocohventionalameloblastoma

Oral Surg Oral Med Oral Pathol. 1983 Jul;56(1 ):54-60

6. Matsumoto Y, Mizoue K, Seto K. Atypical plexiformameloblastoma with dentinoid: adenoid ameloblastoma

with denti[1oid.J Oral Pathol Med. 2001 Apr;30(4)::'51-4

7. Orlowski WA, Doyle JL, Salb R. Unique odontogenictumour with dentinoge[1esisand features of L;nicystic

- -- - ---

Three histologic types are described: the intraluminal,the mural (within the cystic wall) and the plexiformunicystic ameloblastoma. The intraluminal andplexiform are treated with curettage. Mural unicysticameloblastoma is treated with partial resection,especially when it involves the full thickness of thewall.Patients should be placed on follow-up for morethan five years. In this article, we have attemptedto review the literature concerning the plexiformunicystic ameloblastoma, and have presented ourexperience in treating the same.

- - - - - -- - ~ - -

plexiform ameloblastoma. Oral Surg Oral Med OralPathol. 1991 Jul;72(l):91-4.

8. Gardner DG, Morton TH Jr, Worsham JC Plexiform

unicystic ameloblastoma of the maxilla.oral Surg OralMed Oral Pathol. 1987 Feb; 63(2):221-3.

9. Navarro CM, Principi SM, Massucato EMS and Sposto MR.

Maxillary unicystic ameloblastoma. Dentomaxillofacial

Radiology (2004)33, 60-62

10. Leider AS, Eversole LR, Barkin ME. Cystic ameloblastoma:

A clinicopathological analysis. Oral Surg Oral Med Oral

Pathol 1985; 60:624-30

11. Paikkatt VJA, Sreedharan SB. Kannan VPC Unicystic

ameloblastoma of the maxilla: a case report. J Indian SocPedod Prev Dent2007;26(2):116-110

12. Tie JL and Motoo K. Reviewing the UnicysticAmeloblastoma: A Clinicopathologically Distinct Entity. I

Oral Medicine & Pathology Vol. 2 (1997) .NO.2 pp.61-68

13. Pilch BZ. Head and Neck Surgical Pathology. Lippincott

Williams &Wilkins, 2000 p-214.

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CIi n ica 1 Dentistry, Mum ba i 21October 2009