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 Table of Contents  
CASE REPORT
Year : 2017  |  Volume : 12  |  Issue : 4  |  Page : 284-288

Plexiform unicystic ameloblastoma: A rare variant of ameloblastoma


Department of Oral Medicine and Radiology, Sharad Pawar Dental College and Hospital, DMIMS (DU), Wardha, Maharashtra, India

Date of Web Publication17-May-2018

Correspondence Address:
Dr. Suwarna M Bhalerao
Sharad Pawar Dental College and Hospital, DMIMS (DU), Sawangi (M), Wardha, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdmimsu.jdmimsu_30_18

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  Abstract 


The term plexiform unicystic ameloblastoma (UA) refers to a pattern of epithelial proliferation that has been described in the cystic cavity. Due to the unilocular presentation, it is commonly misdiagnosed with an odontogenic (dentigerous) cyst. However, they may often behave clinically as biologically aggressive tumors. The location of the UA within the jawbones shows a marked predominance of the mandible irrespective of the variant. The posterior mandible, including the ascending ramus, is the region most often affected in both variants. In the present case too, the ramus was primarily involved. These tumors show a high incidence of cortical perforation, tooth resorption, and a high rate of recurrence after simple enucleation. Hence need to be carried out of segmental resection due to the extensive size of the lesion. This case report aims to provide an insight into this biologically and radiographically distinct entity. An accurate and timely diagnosis of the character and extent of UA should be done which is only possible after a thorough microscopic examination of the lesion. A literature review on the topic has been added along with a case report highlighting the approach of diagnosis and management of such ameloblastomas.

Keywords: Computed tomography, mandible, multilocular, orthopantomogram, radiolucency, three-dimensional computed tomography, variant of ameloblastoma


How to cite this article:
Bhalerao SM, Lohe VK, Bhowate RR, Mohod SC, Patel S. Plexiform unicystic ameloblastoma: A rare variant of ameloblastoma. J Datta Meghe Inst Med Sci Univ 2017;12:284-8

How to cite this URL:
Bhalerao SM, Lohe VK, Bhowate RR, Mohod SC, Patel S. Plexiform unicystic ameloblastoma: A rare variant of ameloblastoma. J Datta Meghe Inst Med Sci Univ [serial online] 2017 [cited 2019 Aug 17];12:284-8. Available from: http://www.journaldmims.com/text.asp?2017/12/4/284/232579




  Introduction Top


Ameloblastoma is the most common odontogenic neoplasm. Churchill is credited with the first use of the term ameloblastoma in 1934.[1] A thorough description of ameloblastoma was given by Falkson in 1879, and since then, thousands of reports on ameloblastoma have been published.[1]

The relative frequency of unicystic ameloblastoma (UA) has been reported as 5% and 22%. Robinson and Martinez, in 1977, were the first to describe UA and to call for recognition of the entity.[2] Plexiform UA is a relatively rare variant of UA. We report a case of plexiform UA of the mandible in a 25-year-old female.


  Case Report Top


A 25-year-old female patient reported with the chief complaint of swelling on the left side of lower jaw for the past 7 months. She noticed a swelling in the lower jaw in the posterior region, which was initially small in size and gradually increased to the present size. It was initially painless, but the patient now complains of mild intermittent pain, occasionally for the past 10 days and numbness and paraesthesia over swelling and the left side of lower lip for the past 15 days. There were no history of previous consultation and any such swelling in the past.

Extraoral examination revealed a solitary swelling in the left mandibular molar ramus area. The swelling was roughly oval with an approximate size of 5 cm × 4 cm. The margins of the swelling were diffuse. The skin overlying the swelling was smooth and normal in color, lobulation seen on left angle of the mandible. On palpation, the temperature of overlying skin of swelling was not raised. The consistency of the swelling was bony hard. Mediolateral expansion of the cortical plates was noted at molar ramus region of the mandible. A single left submandibular lymph node of size approximately 2 cm–1.5 cm was noted, which was slightly tender and mobile.

Intraoral examination revealed a single painful, bony hard swelling present in 36, 37, 38 and retromolar area, slightly obliterating the pterygopalatine raphe. Expansion of buccal and lingual cortical plate was noted. Tilted 38, no carious tooth present with 37 and 38, no periodontal pocket present with 37 and 38 [Figure 1].
Figure 1: Intraoral examination revealed bony hard swelling present in 36, 37, 38, and retromolar area, slightly obliterating the pterygopalatine raphe and tilted 38, buccal and lingual cortical plate expansion was noted

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Provisional diagnosis on clinical examination was made as ameloblastoma differential diagnosis of, odontogenic keratocyst, dentigerous cyst associated with 38, calcifying odontogenic cyst, calcifying epithelial odontogenic tumor and ameloblastic fibroma was considered.

Radiographic examination of the lesion (orthopantomogram [OPG]) showed a well-defined, multilocular radiolucency, with corticated borders involving the left side of the mandible which extended anteroposteriorly from the mesial of 36 to the posterior border of the ramus of the mandible and superoinferiorly from coronoid notch to the inferior border of the mandible. The presence of scalloping border in the left ascending ramus of mandible, thinning of cortication present in the lower border of the mandible, lobulations seen on the inferior cortex of mandible, loss of cortication seen on the anterior border of the ramus of the mandible. Resorption of the distal surface of the root of the mandibular first, second, and third molar was also noted [Figure 2]. Peripheral ameloblastoma (PA) mandible view showed that buccal cortical plate expansion [Figure 3].
Figure 2: Orthopantomogram showed that multilocular radiolucency involving the molar and ramus of the left side of mandible causing thinning of cortication present in the lower border of the mandible

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Figure 3: Peripheral ameloblastoma mandible view show that buccal and lingual cortical plate expansion

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Computed tomography (CT) and three-dimensional (3D) CT scan of the lesion showed a unilocular osteolytic lesion in the posterior part of body and ramus of the mandible. Buccal and lingual cortical plate expansion was noted [Figure 4] and [Figure 5].
Figure 4: In axial and coronal view showed that there is lytic expansile lesion of the ramus of the left mandible of size 5.8 cm × 4 cm with cortical thinning and loss of integrity. There is soft-tissue density and few calcific foci within

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Figure 5: Three-dimensional computed tomography scan view showed that buccal and lingual cortical plate expansion was noted

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Routine hemogram was performed, and all the blood indices were within normal limits. An incisional biopsy was then performed, which on histopathologic examination revealed a cystic cavity lined by odontogenic epithelium and a connective tissue capsule. Epithelium shows palisaded basal layer resembling ameloblast-like cells and a superficial layer showing stellate reticulum-like cells. The connective tissue was dense, fibrous with collagen fibers arranged haphazardly. Numerous engorged and dilated blood vessels were seen. From the above clinicopathological features, a diagnosis of UA was made.

The patient then underwent a mandibular segmental resection involving condyle and reconstruction was done with 2.7 mm titanium reconstruction plate and iliac crest graft, under general anesthesia [Figure 6].
Figure 6: Intraoperative photographs

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Healing was uneventful. The patient was followed up after 1 month with a radiographic evaluation which showed complete healing of wounds and well-maintained graft [Figure 7].
Figure 7: Postoperative orthopantomogram

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We received a segmental resected specimen involving condyle, coronoid process, up to ascending ramus, which showed perforation in the anterior border of ascending ramus [Figure 8]. Moreover, radiographic evaluation of resected specimen showed multilocularity like a plexus form involving condyle, coronoid process, up to ascending ramus, which showed perforation in the anterior border of ascending ramus [Figure 9].
Figure 8: Resected specimen

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Figure 9: Radiograph of the resected specimen

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Histopathological examination of the excisional biopsy specimen showed lesional tissue that consisted of a cystic cavity lined by odontogenic epithelium and connective tissue capsule. The epithelium showed cuboidal or columnar basal cells with hyperchromatic nuclei, nuclear palisading with polarization, cytoplasmic vacuolization with intercellular spacing, and subepithelial hyalinization and superficial [Figure 10].
Figure 10: H and E stained section showing ameloblastic cystic epitheliums showing intraluminal proliferation in the form of plexiform pattern ([a] H and E, ×100 and [b] H and E, ×40). Intraluminal exophytic masses (subgroup 1.2 or plexiform unicystic ameloblastoma) [c] intraluminal exophytic masses (subgroup 1.2 or plexiform UA)

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Tissue material resembling an odontogenic keratocyst lining was not observed, even with serial sections of tissue. Hence, the possibility of ameloblastic transformation of odontogenic keratocyst was also excluded.

According to the classification suggested by Ackermann et al.,[3] it was classified as UA subgroup 1.2 which is also known as plexiform UA.


  Discussion Top


The UA, a variant of ameloblastoma, is reported to have less aggressive biologic behavior and lower recurrence rate than the classic solid or multicystic ameloblastoma. Although the UA is a “cystic” appearing lesion on gross examination, subsequent microscopic examination shows the presence of ameloblastoma within the cyst wall.[3]

There are four subtypes or variants of ameloblastomas which can presently be distinguished:[3]

  1. The classic solid/multicystic ameloblastoma (SMA)
  2. The UA
  3. The PA
  4. The DA, including the so-called hybrid lesions.


Before the report by Robinson and Martinez, this variant had been referred to as a mural or intraluminal ameloblastoma. The minimum criterion for diagnosing a lesion as UA is the demonstration of a single (often macro-) cystic sac, with an odontogenic (ameloblastomatous) epithelium, which is usually present only in focal areas.

The histologic features of UA have been established by several authors, all of whom recognize various subtypes. The most accepted histologic classification of UA is that suggested by Ackermann et al.[3] who classified it into following four histologic subgroups:

  • (1) Luminal UA
  • (1.2) luminal and intraluminal UA
  • (1.2.3) luminal, intraluminal, and intramural UA
  • (1.3) luminal and intramural UA.


The luminal type of tumor is called UA subgroup (1) which is defined as a cystic cavity lined by an epithelial lining of which parts show transformation to cuboidal or columnar basal cells with hyperchromatic nuclei, nuclear palisading with polarization, cytoplasmic vacuolization with intercellular spacing, and subepithelial hyalinization. This definition was originally suggested by Vickers and Gorlin.[4]

UA subgroup (1.2) shows simple and intraluminal features. The intraluminal proliferation of ameloblastic epithelium in the form of plexiform pattern. Hence, this subgroup is sometimes referred to as the plexiform UA.

The term plexiform UA refers to a pattern of epithelial proliferation that has been described in the cystic cavity. Due to unilocular presentation, it is commonly misdiagnosed as an odontogenic (dentigerous) cyst. However, they may often behave clinically as biologically aggressive tumors. The location of the UA within the jawbones shows a marked predominance of the mandible irrespective of the variant. The posterior mandible, including the ascending ramus, is the region most often affected in both variants. In the present case too, the ramus was primarily involved.

UA subgroup (1.2.3) covers cases where there is an occurrence of intramural ameloblastoma tissue as well as subgroup (1.2) features. The last subgroup (1.3) exhibits a cyst with a luminal lining in combination with intramural nodules of SMA tissue.

It is important to stress that these four subgroups occur in both the dentigerous and the nondentigerous variants. The present case shows the presence of plexiform ameloblastoma in continuity with the cyst lining proliferating into the cystic lumen and hence was diagnosed with subgroup (1.2) plexiform UA.

Philipsen and Reichart [5] in their critical review of 193 cases of UA divided the material into two categories: histologically verified UAs associated with an unerupted tooth and UAs lacking an association with an unerupted tooth. The present case was not associated with any unerupted tooth so that this tumor can be termed as nondentigerous variant.

The cases diagnosed with dentigerous cyst occurred in much younger patients (mean 16.5 years) than those diagnosed as nondentigerous (mean 35.2 years).[5] In contrast to this finding, the present case was of nondentigerous type, but it has occurred in the second decade of life.

In regard to gender distribution, the UA dentigerous variant shows a slight male predominance with a male:female ratio of 1.6:1. However, when the tumor is not associated with an unerupted tooth, the gender ratio is reversed to a male:female ratio of 1:1.8.[5] Hence, although the nondentigerous variant is seen more commonly in females, it was not so in male patient.

The location of the UA within the jawbones shows marked predominance of the mandible irrespective of the variant. The posterior mandible, including the ascending ramus, is the region most often affected in both variants5. In the present case too, the ramus was primarily involved. The radiographic appearance of all UAs is divided into the two main patterns, unilocular and multilocular; there is clear predominance of the unilocular configuration in all studies where this feature was evaluated. This predominance was exceptionally marked for the dentigerous variant where the unilocular: multilocular ratio was 4.3:1.[6] For the nondentigerous type this ratio was 1.1:1.

Leider et al. proposed three pathogenic mechanisms for the evolution of UA: (1) the reduced enamel epithelium associated with a developing tooth undergoes. (2) ameloblastomas arise in dentigerous or other types of odontogenic cysts in which the neoplastic ameloblastic epithelium is preceded temporarily by a nonneoplastic stratified squamous epithelial lining; and (3) a solid ameloblastoma undergoes cystic degeneration of ameloblastic islands with subsequent fusion of multiple microcysts and develops into a unicystic lesion.[7]

Li et al. found that all areas of UA lining contained significantly more PCNA positive cells than dentigerous cyst linings even in areas where epithelial morphology was similar to that of the dentigerous cyst lining. This finding favored the concept that UAs are de novo cystic neoplasms.[8]

Li et al. did not find a true dentigerous arrangement in any of their seven cases of the dentigerous variant. This finding was interpreted as an argument against the hypothesis that UA may originate from a preexisting dentigerous cyst.[8] Similar observations were made by Philipsen et al.[9] when they examined the dentigerous appearance characteristic of another odontogenic tumor, the follicular variant of the adenomatoid odontogenic tumor (AOT). The lack of a true dentigerous cyst-impacted tooth relationship did not support the AOT originating from a preexisting dentigerous cyst but rather favored the “envelopmental” concept, that is, an unerupted tooth being embedded in an expanding tumor mass, whether cystic or solid.

Immunocytochemical markers for lectins (Ulex europaeus agglutinin I and Bandeiraea simplicifolia agglutinin I) and proliferating cells (proliferating cell nuclear antigen and Ki-67) may be helpful in differentiating UA from any other cyst [8],[10],[11] Studies should be conducted to find whether are truly tumorous proliferation or only represent a nonneoplastic, plexiform epithelial hyperplasia.

Various treatment modalities for plexiform UA have been used such as enucleation, enucleation followed by application of Carnoy's solution, marsupialization followed by surgery, and segmental resection. The recurrence rate after enucleation alone is the highest (30.5%), while resection of PUA results in the lowest recurrence rate (3.6%).[12]

In our case, segmental resection was carried out due to the extensive size of the lesion.


  Conclusion Top


In most cases, unilocular lesions are diagnosed with odontogenic cyst both clinically and radiographically. Hence, the chances of treating the lesion conservatively are more. Enucleation or excisional biopsy is the most preferred and planned treatment in case of odontogenic cysts. An accurate and timely diagnosis of the character and extent of UA should be done which is only possible after a thorough radiographic and microscopic examination of the lesion. We would like to emphasize the importance of the radiographic evaluation using OPG, CT, and 3D CT for to evaluate the extend of lesion and involovenment of surrounding structures and microscopic examination for diagnosis of the character and extent of UA. So of all lesions mimicking odontogenic cyst prior to the treatment plan. Adequate radical resection of UA s is important to avoid further complications and recurrence.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Robinson L, Martinez MG. Unicystic ameloblastoma: A prognostically distinct entity. Cancer 1977;40:2278-85.  Back to cited text no. 1
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2.
Iordanidis S, Makos C, Dimitrakopoulos J, Kariki H. Ameloblastoma of the maxilla. Case report. Aust Dent J 1999;44:51-5.  Back to cited text no. 2
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3.
Ackermann GL, Altini M, Shear M. The unicystic ameloblastoma: A clinicopathological study of 57 cases. J Oral Pathol 1988;17:541-6.  Back to cited text no. 3
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4.
Vickers RA, Gorlin RJ. Ameloblastoma: Delineation of early histopathologic features of neoplasia. Cancer 1970;26:699-710.  Back to cited text no. 4
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5.
Philipsen HP, Reichart PA. Unicystic ameloblastoma. A review of 193 cases from the literature. Oral Oncol 1998;34:317-25.  Back to cited text no. 5
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6.
Eversole LR, Leider AS, Strub D. Radiographic characteristics of cystogenic ameloblastoma. Oral Surg Oral Med Oral Pathol 1984;57:572-7.  Back to cited text no. 6
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7.
Leider AS, Eversole LR, Barkin ME. Cystic ameloblastoma. A clinicopathologic analysis. Oral Surg Oral Med Oral Pathol 1985;60:624-30.  Back to cited text no. 7
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8.
Li TJ, Browne RM, Matthews JB. Expression of proliferating cell nuclear antigen (PCNA) and ki-67 in unicystic ameloblastoma. Histopathology 1995;26:219-28.  Back to cited text no. 8
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9.
Philipsen HP, Samman N, Ormiston IW, Wu PC, Reichart PA. Variants of the adenomatoid odontogenic tumor with a note on tumor origin. J Oral Pathol Med 1992;21:348-52.  Back to cited text no. 9
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10.
Li TJ, Browne RM, Matthews JB. Epithelial cell proliferation in odontogenic keratocysts: A comparative immunocytochemical study of ki67 in simple, recurrent and basal cell naevus syndrome (BCNS)-associated lesions. J Oral Pathol Med 1995;24:221-6.  Back to cited text no. 10
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11.
Saku T, Shibata Y, Koyama Z, Cheng J, Okabe H, Yeh Y, et al. Lectin histochemistry of cystic jaw lesions: An aid for differential diagnosis between cystic ameloblastoma and odontogenic cysts. J Oral Pathol Med 1991;20:108-13.  Back to cited text no. 11
    
12.
Lau SL, Samman N. Recurrence related to treatment modalities of unicystic ameloblastoma: A systematic review. Int J Oral Maxillofac Surg 2006;35:681-90.  Back to cited text no. 12
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]



 

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