Ameloblastoma –Adding perspectives - ssdctumkur.org · Ameloblastoma Volume 1 Issue 2 September 2010 11 Journal of Dental Sciences and Research Review Ameloblastoma –Adding perspectives

Ameloblastoma

Volume 1 Issue 2

September 2010

11 Journal of Dental Sciences and Research

Review

Ameloblastoma –Adding perspectives

Dr.Laxmidevi BL1, Dr.Kokila G2, Dr.Jyothi Mahadesh3.

1Senior Lecturer, 2Reader, 3Prof. and H.O.D., Department of Oral Pathology and

Microbiology, Sri Siddhartha Dental College and Hospital, Tumkur, Karnataka.

Abstract:

Ameloblastomas are very common odontogenic tumours. The knowledge

about this tumour is gaining greater importance because of its emerging

variants. It is very essential to know the clinical, radiographical and

histopathological features of all the subtypes of ameloblastoma along with

their behavioural and prognostic characteristics. This article aims at

reviewing and presenting the newer perspectives of the subtypes of

ameloblastoma with more emphasis on UAs (unicystic ameloblastomas), DAs

(Desmoplastic ameloblastomas), and HLAs (hybrid lesion of ameloblastoma)

from the existing literature.

Journal of Dental Sciences & Research 1:2: Pages 11-22

Introduction

In humans, tumors of

odontogenic tissues are

comparatively rare, comprising of

about 1% of all jaw tumors.

Ameloblastomas constitute almost

half (48.9%) of the odontogenic

tumors with female-to-male and

maxilla-to-mandible ratios of 1:1.7

and 1:8 respectively.1 The WHO

defines it as locally invasive

polymorphic neoplasm consisting of

proliferating odontogenic

epithelium,which usually has a

follicular or plexiform pattern lying

in fibrous stroma.2,3This tumour is

discussed to be derived from

serre’s epithelial cell rests, the

epithelial cell rest of malassez,

epithelium of odontogenic cysts

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and basal cell layer of gingiva or

oral mucosa4,5

Clinically ameloblastomas

appear as aggressive odontogenic

tumours often asymptomatic and

slow growing with no evidence of

swelling. It can even cause

symptoms such as swelling, dental

malocclusion, pain and paresthesia

of affected area.6 Usually

radiographs appears as a well

demarcated unilocular or

multilocular radiolucency that may

or may not be associated with

unerrupted tooth.

Histopathologically ameloblastoma

exhibits proliferating odontogenic

epithelium within a background of

fibrous stroma.7 Since

ameloblastoma shows histologic

patterns which vary greatly, a

number of subtypes can be

distinguished.5

Ameloblastoma is notorious

for its recurrences although it is

benign in nature. Due to this it is of

great importance not only to the

surgeons but also to the private

practioners of dentistry. Therefore

this article aims at discussing the

diversities of clinical, radiographical

and histopathological features of

subtypes of ameloblastoma

reviewing from the existing

literature.

Discussion:

Ameloblastomas are an

enigmatic group of oral tumours.8A

series of genetic and molecular

alterations appear to promote the

development and progression of

the odontogenic tumours via

multiple steps. Some of these

include Oncogenes eg. Fibroblast

growth factor receptor,

Transcription factors eg.myc,

tumour suppressor genes eg.

Retinoblastoma, Oncoviruses

eg.HPV, EBV etc.9

In the literature unicystic and

desmoplastic variants are now

recognized as clinically,

radiographically and

histopathologically distinct entities,

with differing prognostic

significance.2, 10. Hence, based on

all these features along with

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behavioural and prognostic

characteristics, subtypes or

variants of ameloblastomas can be

presently distinguished as follows.1

1.The classic solid/ multicystic

ameloblastoma (SMA)

2.The unicystic ameloblastoma

(UA)

3.The peripheral ameloblastoma

(PA)

4.The desmoplastic ameloblastoma

(DA), including the so-called hybrid

lesions.

In a recent study done on

3,677 ameloblastoma cases,

clearly demonstrated that it is not

appropriate to diagnose the

ameloblastoma without specifying

the type.11

Unicystic Ameloblastoma

Unicystic Ameloblastoma was

first described by Robinson and

Martinez in 1977.12,13

The term ‘unicystic’ is

derived because of its macro- and

microscopic appearance of the

Lesion.11 The incidence of UAs is 5-

22% of all types of

ameloblastomas.14 Younger

patients are commonly affected,

with 50% of cases being diagnosed

during the second decade of life.

The average age in one large

series was found to be 23

years.15,16

Slight male predilection with

a male:female ratio of 1.6:1 is

seen. However, when the tumor is

not associated with an un-erupted

tooth, the gender ratio is reversed

to a male to female ratio of

1:1.8.Depending on the association

of impacted tooth, UA can be

divided into 2categories.11

1. Histologically verified UAs which

are associated with an unerrupted

tooth (dentigerous variant)

2. UAs lacking an association with

an unerrupted tooth (non

dentigerous variant).

Most common site is the

mandible, irrespective of the

variant. The ratio of the maxilla:

mandible is 1:7 for the dentigerous

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variant, versus 1:4.7 for the

nondentigerous type.17

Radiographically, unilocular

and multilocular patterns of UAs

exist. Unilocular pattern seen

predominantly. Eversole LR et al

identified predominant

radiographical

patterns for UA: unilocular,

scalloped, macromultilocular,

pericoronal, interradicular,

or periapical expansile

radiolucencies. 1When the UAs

associated with impacted tooth the

diferential diagnosis is dentigerous

cyst. UAs that are not associated

with an impacted tooth may mimic

a residual cyst or a keratocyst.14

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.UA should be differentiated

from odontogenic cysts because

the former has higher rate of

recurrence than later. In a

clinicopathological study of 57

cases of UA ,Ackerman et.al

classified this entity into 3

histolologic groups.12

GroupI:Luminal UA [tumour

confined to the luminal surface of

the cyst:(Fig.1)]

Fig.1: Photomicrograph shows cystic wall

lined by ameloblastomatous epithelium

and stellate reticulum like

cells(CTW:Connective tissue

wall,AE:Ameloblastomatous

epithelium)[Heamatoxyllin& Eosin stain

x10]

GroupII: Intraluminal/plexiformUA

[nodular proliferation in to the

lumen without infilteration of the

tumour cells in to the

connective tissue wall:(Fig.2)]

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Fig.2:Photomicrograph with Intraluminal

nodular/papillomatous proliferation of

epithelium. (NP: Nodular proliferation)

[Heamatoxyllin & Eosin stain x10]

GroupIII: Mural UA [invasive

islands of ameloblastomatous

epithelium in the connective tissue

wall not involving the entire

epithelium:(Fig.3)]

Fig.3: Intramural ameloblastomatous

epithelial proliferation. (CTW:Connective

tissue wall,AE:Ameloblastomatous

epithelium) [Heamatoxyllin & Eosin stain

x10]

Histological subgroups (modified

after Ackerman et.al) by Philipsen

and Reichart.11

Subgroup1: Luminal UA

Subgroup1.2: Luminal and

intraluminal

Subgroup1.2.3: Luminal,

intraluminal and intramural

Subgroup1.3: Luminal and

intramural.

Therefore when UAs removed

in toto, the surgical specimen is

that of partially or totally collapsed

cystic sac. By careful examination

of the inner and outer aspects of

the cyst wall, it may be possible to

spot characteristics of UA features

such as one or several intraluminal

papilloma-like tissue proliferation

and/or intramural focal thickenings

or nodules. Lack of these findings

does not however exclude a

diagnosis of UA. The diagnosis of

UA can only be made histologically

and cannot be predicted

preoperatively on clinical or

radiographic grounds. Examination

of the entire lesion through

sectioning at many levels is

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mandatory for securing the final

diagnosis.11,18

The UAs diagnosed as

subgroups 1 and 1.2 may be

treated conservatively where as

subgroups 1.2.3 and1.3 showing

intramural growths must be

treated radically same as SMA.11

Recurrence is also related to

histological subtypes of UAs with

those invading fibrous wall having

the rate of 35.7% but others only

6.7%.19

Recurrence rate for

enucleation alone is 30.5%, where

as 3.6% for resection,12 compared

to 0-25% chances in conventional

ameloblastoma after resection.8

Desmoplastic Ameloblastoma

Recently, the desmoplastic

variant of ameloblastoma is

considered as a distinct clinical,

radiographical and pathologic

entity and classified as separate

category by WHO classification of

odontogenic tumours.10

DAs comprises of 4 to 13%

of all the ameloblastomas. Eversole

and co-workers are, credited for

the first publication on DA in

English literature It is named so

because of unusual

histomorphology, including the

extensive collagenisation or

desmoplasia.20,21

Average age of occurance is 42.9

yrs compared to 35.9 of SMA.No

gender predilection. In most of the

cases presents as painless swelling

with tumour size varying between

1.0 and 8.5 cms at the greatest

diameter. In the study of

Phillipsen, maxilla:mandible ratio

was 1:0.9.This is in sharp contrast

to the SMA showing 1:5.4. 22

Vast majority of DAs are

seen in the anterior region till

premolar portions of the jaw.

Approximately half of them are

seen in the maxilla.7Only about

5.4% cases were seen in the

mandibular molar region as

opposed to 39% of SMA. An

association of DA and unerrupted

or impacted tooth has been found

in only about 3.4% of cases, as

against the 8.7% among SMA.22

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The radiographic features of

DA differ from those of SMA. DAs

frequently presents as diffuse,

mixed radiolucent-radio-opaque

lesion with ill defined borders,

often misdiagnosed as fibro-

osseous lesion(Fig.4).23,24,25 The

illdefined borders may explain the

infiltrative behaviour of DA.22

Fig.4: Radiograph showing ill-defined

borders of the DA (Courtesy: J Can Dent

Assoc 2004; 70(2):100–4)

Waldron and El Mofty26

described histologic appearance of

DA as small ovoid islands and

narrow cords of odontogenic

epithelium widely separated by

dense ,moderately cellular fibrous

connective tissue. Typical

ameloblastic columnar cells may be

scant and the peripheral palisading

may be absent. The center of the

epithelial islands may appear

hypercellular with spindle shaped

or squamotoid epithelial cells.22,24

Extensive stromal desmoplasia

(Fig.5) is a prominent feature, with

abundant thick collagen fibres that

seems to compress or squeeze the

odontogenic epithelial islands from

the periphery. Myxoid changes of

the stroma may be observed

surrounding the odontogenic

epithelium. Formation of

metaplastic bone trabeculae

rimmed by active osteoblasts has

been described in several

cases.The desmoplastic stroma of

DA is not scar tissue but newly

produced connective tissue.22,27

Fig.5:Photomicrograph showing extensive

desmoplasia with compressed/squeezed

odontogenic epithelial islands

(magnification x5)[Courtesy: J Can Dent

Assoc 2004; 70(2):100–4]

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DA showed similar

recurrence rate (15.9%) as that of

SMA.Krezler even reported the

higher recurrence rate than other

types of ameloblastomas. The

reason for this could be because

radiographically DAs can be

misdiagnosed as fibro-osseous

lesions and also they present with

ill-defined borders making it

difficult to assess the exact

interface of the lesion with normal

bone.Along with all these, it is

more commonly seen in maxilla

which may produce early invasion

of the adjacent

structures.24.According to Phillipsen

et.al radiographically ill-defined

borders suggest an infiltrative

process and aggressive nature with

propensity to recur.28,29 Resection

and enucleation are the main

treatment modalities of DAs even

though biological behaviour and

prognosis, and the proper

treatment stratergies for DAs are

not entirely defined so for.

Prospective studies with regular

and long term follow-up is required

to provide the necessary

information.Till then DAs has to be

treated as that of SMA.24

Hybrid Lesion of

Ameloblastoma (HLAs)

The HLAs was first described

by Waldron and El-Mafty. 26It is a

tumour variant where histologically

areas of follicular or plexiform

ameloblastoma coexist with areas

characteristics of DA.30 It has been

suggested that the hybrid lesion

should be considered a collision

tumour. Whereas many more cases

with detailed clinical and

radiographic data and

corresponding analysis are needed

to clarify the biological behaviour

of this tumour.22

Conclusion

Eventhough ameloblastomas

are common odontogenic tumours,

they present challenge in both

diagnosis and treatment, because

of diversities in clinico-pathological

and radiographic features.

Therefore this article is an attempt

at adding the current newer

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perspectives, by discussing the

clinico-pathological and

radiographic variations of UAs, DAs

and little about HLAs to the already

existing types of ameloblastomas,

for a better and appropriate patient

management.

Conflict of Interest Statement:

None Declared

Acknowledgements

We sincerely thank Dr. John O Keffe, Editor in chief, J Can Dent Assoc, for

permitting to use the illustrations (fig 4 & fig 5 ) of desmoplastic

ameloblastoma. We also thank Dr. Suhas, Professor and HOD, Oral Medicine

and Radiology, Sri Siddhartha Dental College, for his constant support in

bringing up this work.

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Corresponding Author

Dr. Laxmidevi BL,

Senior Lecturer,

Department of Oral Pathology and

Microbiology, Sri Siddhartha Dental

College and Hospital, Tumkur,

Karnataka- 572107

Ph.no:9844391171, E-

mail:[email protected]

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Ameloblastoma –Adding perspectives - ssdctumkur.org · Ameloblastoma Volume 1 Issue 2 September 2010 11 Journal of Dental Sciences and Research Review Ameloblastoma –Adding perspectives