| Abstract|| |
Ameloblastoma is a true benign neoplasm of odontogenic epithelial origin mostly seen in the mandible. After odontoma, it is the second most commonly seen odontogenic neoplasm. Ameloblastoma comprises of several clinical, radiological and histological varieties, making it the most significant odontogenic neoplasm. Among these, the unicystic type is the least explored due to the fewer numbers of reported cases. Clinically and radiographically, it represents a cyst, but displays classic ameloblastomatous epithelial lining part of the cyst cavity, with or without intraluminal and/or mural tumor growth. We present an unusual case of unicystic ameloblastoma showing mural proliferation with mixed histological pattern [Plexiform, Follicular and Acanthomatous] of the mandible in a 32-year-old male.
Keywords: Follicular ameloblastoma, mural proliferation, plexiform pattern, unicystic ameloblastoma
|How to cite this article:|
Ahmed SP, Gunasekaran N, Arunachalam P, Annasamy RK. Mural unicystic ameloblastoma with multifarious histopathological patterns: An exquisite case report. Indian J Dent Res 2020;31:803-6
|How to cite this URL:|
Ahmed SP, Gunasekaran N, Arunachalam P, Annasamy RK. Mural unicystic ameloblastoma with multifarious histopathological patterns: An exquisite case report. Indian J Dent Res [serial online] 2020 [cited 2021 Jan 28];31:803-6. Available from: https://www.ijdr.in/text.asp?2020/31/5/803/306452
| Introduction|| |
Mandibular swellings can be instigated by various benign lesions of both odontogenic and non-odontogenic origin. Ameloblastoma is the second most common tumor of odontogenic origin which develops from epithelial component of the odontogenic apparatus. They have multiple histological variants and can have high recurrence rates, if inadequately treated. As per the WHO 2017 (4th edition) classification, ameloblastoma is classified as Ameloblastoma-conventional type, Ameloblastoma-unicystic type, Ameloblastoma-extraosseous/peripheral type and malignant subtypes. The term 'Unicystic Ameloblastoma' was adopted in the second edition of the International Histologic Classification of Odontogenic Tumors and was first described by Robinson and Martinez in 1977. 80% of this lesion is said to occur exclusively in the mandibular third molar area, where most cases are associated with unerupted teeth and seen in young patients during the second decade of life. They are slow growing and are relatively locally aggressive. Although the term unicystic would imply a unilocular radiographic appearance, the lesion can sometimes have a multilocular radiographic appearance as well. Unicystic ameloblastomas are those cystic lesions that show clinical and radiographic characteristics of an odontogenic cyst but on histologic examination show a cystic cavity lined by ameloblastomatous epithelium with or without intraluminal and/or mural proliferations. We thereby illustrate an unusual case of unicystic ameloblastoma-mural type with mixed histological pattern [Plexiform, Follicular and Acanthomatous] of the mandible in a 32-year-old male.
| Case Report|| |
A 32-year-old male patient reported to the Department of Oral Medicine and Radiology with a chief complaint of swelling on the right side of the lower jaw for the past 2 years, associated pain while chewing food for the last 3 months and difficulty in mouth opening. History revealed that the swelling was initially small in size and gradually increased to attain the current size and associated with intermittent, dull pain which was chronic and radiating in nature. Extra oral examination revealed a solitary diffuse swelling on the right side of the lower one-third of the face, measuring approximately 6 x 4 cm extending anteriorly 3 cm short of the chin to the angle of the mandible posteriorly, superiorly from the line joining the corner of the lip and lower margins of ear to the inferior border of mandible, inferiorly. The skin overlying the swelling was stretched, warm, tender and hard to palpate. On intraoral examination, solitary diffuse bicortical swelling was evident on the right side of the mandible obliterating the right buccal and lingual vestibule. On palpation, the swelling was bony hard in consistency and tender. Mouth opening was restricted to about 19 mm interincisal distance.
OPG showed a unicystic expansile lesion on the right side of mandible with displacement of the third molar, and resorption of roots of the first and second molars [Figure 1]. Axial CT revealed a well-defined, expansile, unilocular lytic lesion with scalloped margins on the angle of the right side of the mandible with loss of lingual cortex. Routine blood investigations were done and were found to be within normal limits.
|Figure 1: OPG shows unicystic expansile lesion on the right side of mandible with resorption of roots of 46, 47|
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Based on the clinical, radiographic and CT findings, a provisional diagnosis of ameloblastoma was made. Under local anaesthesia, an incisional biopsy was done and sent for histopathological diagnosis. The histopathological examination revealed a cystic cavity lined by epithelium. The lining epithelium showed ameloblast like basal cells and loosely arranged superficial cells resembling stellate reticulum like cells. In a few areas, the connective tissue wall exhibited odontogenic islands resembling follicular ameloblastoma. Thus, based on histopathological diagnosis of unicystic, ameloblastoma mural type (follicular variant) was given [Figure 2].
|Figure 2: Photomicrograph after incisional biopsy shows cystic cavity lined by odontogenic epithelium with mural proliferation (Haematoxylin and eosin staining, 10×)|
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The treatment plan was for segmental resection with wide margins to avoid a recurrence and subsequent long-term follow-up was planned. Following resective surgery, the specimen was sent for histopathological examination to ensure complete removal of the lesion as well as to substantiate the diagnosis [Figure 3].
Excisional biopsy tissue showed a cystic cavity lined by epithelium with connective tissue wall. The epithelial lining showed flat interface with tall columnar basal cells resembling ameloblast and superficially, the cells were star shaped and loosely arranged resembling a stellate reticulum like cells. In few areas the lining epithelium was highly proliferative; [Figure 4] extending deep into the connective tissue wall in the form of interconnecting strands and cords resembling plexiform ameloblastoma. The strands and cords showed peripherally placed ameloblast like cells and centrally placed stellate reticulum like cells. The connective tissue wall also showed odontogenic islands resembling follicular ameloblastoma. The islands showed peripherally placed ameloblast like cells and centrally placed stellate reticulum like cells with squamous differentiation [Figure 5]. The connective tissue wall was loose to densely arranged with minimal inflammatory component. Based on these findings, the biopsied tissues were histopathologically reported as unicystic ameloblastoma with mural proliferation exhibiting Plexiform and Follicular pattern with acanthomatous change. The patient was followed up for the past 2 years with no recurrence so far.
|Figure 4: Photomicrograph shows proliferative cystic lining epithelium, extending deep into the connective tissue wall in the form of interconnecting strands, cords and islands. (Haematoxylin and eosin staining, 10×)|
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|Figure 5: Photomicrograph shows connective tissue wall showing (plexiform and follicular mural proliferation) with squamous differentiation and keratin pearl formation. (Haematoxylin and eosin staining, 10×)|
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| Discussion|| |
Odontogenic Tumors (OT) are a heterogeneous group of lesions of diverse clinical behaviour and histopathologic types, ranging from hamartomatous lesions to malignancy. The classification of odontogenic tumors is essentially based on interactions between odontogenic ectomesenchyme and epithelium. This dynamic classification is constantly renewed with the addition of new entities and the removal of some older entities.
Unicystic ameloblastoma is a subtype of intraosseous ameloblastoma, consisting of a large single cyst. Unilocular ameloblastoma (UA) is a rare type of ameloblastoma, accounting for about 6% of ameloblastomas. They are likely to present a decade earlier than conventional ameloblastoma. Radiographs often show a unilocular, well-demarcated radiolucency that surrounds the crown of the unerupted tooth, resembling dentigerous cysts. The ratio of mandibular to maxillary unicystic ameloblastoma has been reported to be 13:1. Eversole et al. were able to identify numerous radiographic patterns of UA ranging from well-defined unilocular to multilocular appearances: unilocular, scalloped macromultilocular, pericoronal, interradicular, and periapical expansile radiolucencies. For dentigerous type the unilocular to multilocular ratio is 4.3:1 and for the nondentigerous type, this ratio is 1.1:1,
There can be 3 pathologic mechanisms for the development of UA:
- The reduced enamel epithelium, associated with the developing tooth, undergoes ameloblastic change with subsequent cystic transformation.
- Ameloblastomas arise in dentigerous or other types of odontogenic cysts in which the neoplastic ameloblastic epithelium is preceded temporarily by a non-neoplastic stratified squamous lining.
- Solid ameloblastoma undergoes cystic degeneration of ameloblastic islands with a subsequent fusion of multiple microcysts and then into a unicystic lesion.
Minimum histopathological criteria for diagnosing a unicystic ameloblastoma is based on the Vickers and Gorlin criteria which describes the presence of single cystic sac, which is lined by odontogenic (ameloblastomatous) epithelium with a tall columnar basal layer, subnuclear vacuoles, reverse polarity of hyperchromatic nucleus and a thin layer of edematous, degenerating stellate reticulum like cells on the surface in focal areas. Our case showed a cystic cavity with epithelial lining which was highly proliferative and extended into the connective tissue, suggesting mural type of UA, with few areas showing both plexiform and follicular pattern with squamous differentiation.
In 1988, Ackermann studied 57 cases and categorised unicystic ameloblastoma (UA) in 3 histologic growth patterns:
- Luminal UA (tumor confined to the luminal surface of the cyst);
- Intraluminal/plexiform UA (nodular proliferation into lumen without infiltration of tumor cells into connective tissue wall); and
- Mural UA (invasive islands of ameloblastomatous epithelium in the connective tissue wall not involving the entire epithelium).
Later, another subgrouping was given based on treatment modalities by Philipsen and Reichart:
Subgroup 1: luminal UA;
1.2: luminal and intraluminal UA;
1.2.3: luminal, intraluminal and intramural UA; and
1.3: luminal and intramural UA.
The UA diagnosed as subgroups 1 and 1.2 can be treated conservatively, while subgroups 1.2.3 and 1.3 showing intramural growths require radical resection as for solid or multicystic ameloblastoma.
Traditionally, unicystic ameloblastomas were treated conservatively, regularly by enucleation of the cysts, and recurrence was uncommon. Following enucleation, vigorous curettage of the bone should be avoided as it may implant foci of ameloblastoma more deeply into the bone. Chemical cauterization with Carnoy's solution (powerful fixative that penetrates the cancellous spaces and thus fixes the remaining tumor cells) is also advocated for subgroups 1 and 1.2. Subgroups 1.2.3 and 1.3 have a high risk for recurrence, requiring more aggressive surgical procedures. This is because the cystic wall in these cases have islands of ameloblastoma tumour cells and there may be penetration into the surrounding cancellous bone.
Several additional treatment modalities for UA have been used such as segmental or marginal resection, more conservative treatment such as enucleation and curettage, marsupilization to reduce the size of the lesion followed by second stage surgery. These treatments can be followed by adjunctive therapy together with cryotherapy, thermal or chemical cauterization, and even radiotherapy or chemotherapy. The reported recurrence rate after treatment for unicystic ameloblastoma ranges from 10-25%. There is no adequate evidence to prove which treatment modality is more effective. Lau et al. reported recurrence rates of 3.6% for resection, 30.5% for enucleation alone, 16% for enucleation followed by Carnoy's solution application, and 18% for marsupialization followed by enucleation (where the lesion reduced in size). Despite the high success rate for resection of UA, a more conservative treatment is generally favoured, in order to optimize the quality of life.
Clinically, unicystic ameloblastoma is considered to be a less aggressive tumour with better prognosis. The plausible reason for a bad prognosis is that though the unicystic ameloblastoma is usually cystic, well-localized and surrounded by a fibrous capsule, the tumour can infiltrate the capsule and the surrounding cancellous bone, making it an aggressive tumour.
| Conclusion|| |
Unicystic ameloblastoma is a rare variant of ameloblastoma, which presents with a diversity of clinical, radiological and histopathological features. Radiographically, most of the cases of unicystic ameloblastomas show multilocularity, although unilocular ameloblastomas with a single large unilocular radiolucency have also been reported. These tumours show aggressive behaviour. Hence, it presents a challenge both for its diagnosis and treatment and consideration should be given to plan proper treatment. Finally, this case study adds to the rare case report in the literature of mural unicystic ameloblastoma with plexiform and follicular pattern with acanthomatous change.
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.
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Conflicts of interest
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Dr. Preethi Arunachalam
Department of Oral Pathology, SRM Dental College, Bharathi Salai, Ramapuram, Chennai, Tamil Nadu - 600 089
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]