|Year : 2016 | Volume
| Issue : 1 | Page : 36-41
Unicystic Ameloblastoma Developing into a Hybrid Lesion of Rare Entity - with Review of Literature
Savina Gupta, Mukul Nandkumar Padhye, Gokul Venkateshwar, Sandhya Tamgadge, Hirkani Attarde
Department of Oral and Maxillofacial Surgery, D.Y. Patil University, School of Dentistry, Nerul, Navi Mumbai, Mumbai, Maharashtra, India
|Date of Web Publication||27-Jun-2016|
Department of Oral and Maxillofacial Surgery, D.Y. Patil University, School of Dentistry, Nerul, Navi Mumbai - 400 706, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
Existence of unicystic ameloblastoma with desmoplasia is a seldom occurrence. It was first described by Waldron and El-Mofty in the year 1987 as the term hybrid ameloblastoma. Here, we account a case of hybrid lesion depicting outstanding unicystic, follicular ameloblastoma with desmoplasia and mucus cell differentiation showing inductive changes. The patient is a 38-year-old male with a swelling in the lower right posterior region of the jaw. Radiologically, a mixed radiopaque-radiolucent lesion was sighted in this region. Taking into account of patient's complaint, clinical, radiographic, and histologic features; diagnosis of ameloblastic fibrodentinoma was made. It was followed by complete excision of the tumor. The challenge in the management of this tumor was to render complete excision as recurrence may occur in incomplete removal and also to reconstruct the bony defect to give a moderate cosmetic and functional result to the patient. The excisional biopsy report was established to be of hybrid ameloblastoma. Since there are few cases reported in the past of this lesion, the present case is an addition for better perception of this odontogenic tumor. This article identifies some profound concepts and new developments in the histopathologic design of ameloblastoma and its hybrid variant. It also briefly reviews the literature referring to this rare tumor entity. Considering the characteristics of ameloblastoma, priority of surgical management for hybrid lesion is also described.
Keywords: Desmoplastic, hybrid, unicystic ameloblastoma
|How to cite this article:|
Gupta S, Padhye MN, Venkateshwar G, Tamgadge S, Attarde H. Unicystic Ameloblastoma Developing into a Hybrid Lesion of Rare Entity - with Review of Literature. Indian J Oral Health Res 2016;2:36-41
|How to cite this URL:|
Gupta S, Padhye MN, Venkateshwar G, Tamgadge S, Attarde H. Unicystic Ameloblastoma Developing into a Hybrid Lesion of Rare Entity - with Review of Literature. Indian J Oral Health Res [serial online] 2016 [cited 2019 Jun 15];2:36-41. Available from: http://www.ijohr.org/text.asp?2016/2/1/36/184737
| Introduction|| |
In the field of oral and maxillofacial surgery, hybrid ameloblastoma is a seldom occurrence, ,,, portraying histologically a marked stromal desmoplasia. In treating this type of tumor, it is important to evaluate the clinical types in the lesion, localization, and size of the tumor.
To enhance knowledge of this pathologic entity, we contribute another case of hybrid ameloblastoma.
| Case report|| |
A 38-year-old male patient reported to the department with a chief complaint of pain and swelling in lower right posterior region of the jaw since 6 months. The patient presented a history of enucleation and curettage along with extraction of the third molar for the similar complaint 23 years back. The patient was disease free till this lesion recurred 8 years after initial surgery, requiring second intervention. A local dentist aspirated the cystic cavity along with extraction of the first and second mandibular molars. The size of the swelling subsequently decreased. Presently, the patient endured this lesion once again since last 6 months.
The patient was otherwise in good health, and his medical and family history was noncontributory.
Extraoral examination presented with a swelling in relation to the angle of the mandible on the right side extending anteroposteriorly from body to the angle of the mandible and superoinferiorly from the line corresponding to the tragus of the ear till the angle of the mandible. The overlying skin was smooth and normal in color [Figure 1]. On palpation, swelling was tender, firm, nonfluctuant, and noncompressible. There was no significant lymphadenopathy detected.
On intraoral examination, the overlying mucosa of the lesion was pink in color. Dimensions of the lesion were 4 cm × 3 cm, with well-defined margins, extending anteroposterior from the mandibular second premolar to the anterior border of the ramus of the mandible and superoinferiorly from the edentulous ridge of 46, 47, and 48 obliterating vestibule of the mandible [Figure 2]. On palpation, both buccal and lingual cortices were involved. The swelling was firm, tender, and noncompressible. All neighboring teeth were vital with no evidence of other dental abnormalities.
Orthopantomogram revealed multilocular radiolucency with soap bubble appearance extending from coronoid process till the body of the mandible. The locules had mixed radiolucent and radiopaque appearance [Figure 3].
Computed tomography illustrated an osteolytic, space occupying lesion at the posterior part of the right mandible. The axial section demonstrated buccal and lingual cortical thinning in the area of 46, 47, and 48 regions [Figure 4]. The sagittal section exhibited a multilocular hypodense region ranging from coronoid process till the base of the mandible. Base of the mandible had thinned out [Figure 5]. Three-dimensional computed tomography presented involvement of coronoid process till the distal aspect of the second premolar with a small breach in the buccal cortex involving the inferior alveolar nerve in the lesion [Figure 6].
An incisional biopsy was conducted on the ascending ramus region under local anesthesia. The histopathological diagnosis obtained was ameloblastic fibrodentinoma.
The management was done by segmental resection on the right side of the jaw, from posterior aspect of the second premolar, salvaging the condyle, and coronoid process via extraoral approach [Figure 7]. Immediate reconstruction was done with 2.4 mm locking reconstruction plates.
Excised specimen was sent for histopathological diagnosis. It was reported to be a hybrid lesion of unicystic, follicular, desmoplastic with mucus cell differentiation and numerous foci of inductive changes.
Deviation of the mandible toward the left side was observed after 2 weeks postoperatively [Figure 8]. Patient was evaluated in regular monthly intervals. Patient is apparently disease free, with no marked complaints regarding the surgery since 2 years.
| Discussion|| |
Odontogenic tumors develop from odontogenic epithelium, which has the capability for various differentiations and mesenchymal induction. Histologically, ameloblastoma occurs in different patterns, as plexiform, follicular, basal cell, granular, desmoplastic, and acanthomatous. Hybrid lesion is a variant of ameloblastoma in which follicular and plexiform exist together with areas of pronounced stromal desmoplasia. ,
Hybrid ameloblastoma was first identified by Waldron and El-Mofty in 1987.  It is a benign, locally invading, intraosseous, infiltrative ameloblastoma.  From the review of the literature, hybrid ameloblastoma is rarely found. , So far, only 30 cases of hybrid ameloblastoma have been reported.  They are reported to be 4-13% of all ameloblastomas.  Clinical findings of 26 cases of hybrid ameloblastoma have been summarized in [Table 1].
|Table 1. Clinico pathologic features of 26 compiled cases of Hybrid Ameloblastoma |
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Regarding on age, sex distribution, and site of occurrence of this lesion; it usually appears at the age of 42.9 years, higher for males (45.9 years) than for females (39.7 years), male/female ratio is 1:1. , The usual site of lesion is anterior portion of the jaws,  and the ratio of maxilla/mandible is 1:0.9.  In our case, the lesion was observed in the posterior aspect of the mandible.
Radiologically, conventional ameloblastoma is classified as unilocular or multilocular radiolucency with well-defined borders. The radiographic characteristics of the case in this article demonstrated a combination of two distinctive visual aspects as in mixed radiolucent-radiopaque multilocular areas. This indicates the presence of hybrid lesion of ameloblastoma. Recurrence after initial surgical treatment is an outcome of the infiltrative growth of ameloblastoma through the adjacent bone. This new bone formation leads to mixed radiolucency and radiopacity.  Moreover, most ameloblastomas show multilocularity, whereas unicystic ameloblastomas depict large unilocular radiolucency. Seldom, we encounter a multilocular lesion in unicystic ameloblastoma; which was observed in the present case. 
The unicystic ameloblastoma commonly appears as a cystic lesion with either an intraluminal or an intramural proliferation of the cystic lining.  Histopathological examination of the surgical specimen showed a unicystic ameloblastoma of intraluminal and mural type. Intraluminal proliferation was of plexiform pattern, and mural proliferation showed unusual histopathological findings, which revealed follicular, acanthomatous areas coexisting with desmoplastic areas. This mural picture was similar to the so-called "hybrid lesion of ameloblastoma." The lesion also revealed a distinctive picture of extensive collagenized stroma containing small islands of tumor epithelium with scanty inclination to form cystic structures. The ameloblastoma also displayed evidence of focal mucus cell differentiation [Figure 9]. The occurrence of mucous cells in ameloblastoma is an exceptionally rare phenomenon and up to now 6 cases of ameloblastoma showing mucous cells are reported.  In this article, we make an addition of one more of such a case. This is a unique case report of desmoplastic ameloblastoma with mucous cell differentiation in posterior mandible as all the earlier published cases showed occurrence in anterior jaws. , The probable pathogenesis for mucous cell differentiation expresses the pluripotential character of the odontogenic epithelium.
|Figure 9: (a) Photomicrograph of an incisional biopsy shows odontogenic epithelium consisting of tall columnar ameloblast-like cells and stellate reticulum-like cells suggestive of unicystic ameloblastoma. (b) Photomicrograph of an excisional biopsy shows odontogenic island in the connective tissue capsule. (c) Photomicrograph of an excisional biopsy shows odontogenic island in the connective tissue capsule showing cystic degeneration. (d) Photomicrograph of an excisional biopsy shows desmoplasia with compressed odontogenic island in the connective tissue capsule along with calcifications|
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With respect to histologic features, these hybrid lesions are also known to have a combination of desmoplastic and conventional ameloblastoma.  The odontogenic epithelium occurs as irregular, stellate, or follicular islands and cords; central part frequently appears hypercellular with spindle-shaped or squamatoid cells. Peripheral columnar or cuboidal cells seldom disclose ameloblastic appearance. Therefore, vaguely mimicking a follicular ameloblastoma with acanthomatous characteristics. Furthermore, spectacularly there is extensive stromal desmoplasia with copious thick collagen fibers compressing epithelial islands.  According to Sun et al.,  scattered epithelial nests and extensive desmoplasia were salient features of desmoplastic ameloblastoma. The neoplastic epithelial islands seen in desmoplastic ameloblastoma are small and ameloblastic cells are rare.  A hybrid odontogenic tumor incorporating two distinct lesions is highly uncommon,  and the present case is depicting this seldom occurrence.
In our case, the incisional biopsy report derived was of ameloblastic fibrodentinoma. As preoperative biopsy does not illustrate the entire lesion, it may result in incorrect categorization of the lesion. Thus, the true nature of the lesion is manifested only after the entire specimen is available for microscopy. The treatment plan was formulated according to clinical examination and biopsy reports.
Ameloblastoma is a polymorphic neoplasm for which the surgical intervention is established by a number of clinical and histological factors. The method of surgery consists of radical surgery (segmental resection) and conservative method (enucleation with bone curettage). Aggressive lesions demand more radical surgical approach ensuing large jaw defects. Recurrence rates of ameloblastoma are reportedly as high as 15-25% after radical treatment and 75-90% after conservative treatment.  Of late, the progress in comprehending the biologic conduct of ameloblastoma reveals that unicystic lesions are well localized by the fibrous capsule of the cyst, with few tumors broaching peripheral tissues, whereas multicystic and solid lesions are known to have aggressive infiltration to adjacent tissue.  Gardner recommended that solid and multicystic ameloblastoma should be treated radically, whereas unicystic ameloblastoma can be cured by curettage.  The intraluminal subtype of unicystic ameloblastoma may respond well with enucleation, but the intramural subtype may not; and since this more aggressive treatment is recommended. 
Philipsen et al. advocated treating these kinds of cases such as other variants of infiltrative ameloblastoma till they the diagnosis is histopathologically confirmed.  Sun et al.  reviewed desmoplastic ameloblastoma and concluded that resection reduces recurrence rate as compared to enucleation of the lesion and the average period of recurrence was 36.9 months.
To a large extent, recurrence is the result of performing an inadequate initial procedure. Therefore, radical and aggressive surgery is a more favored option for recurrent ameloblastoma management.  In the present scenario, the patient already had recurrence twice previously; therefore, the preferred choice of surgery was radical resection. Moreover, the prognosis of recurrence appears to be associated with the surgical planning before evaluation of the histologic subtype.
Therefore, complete excision is advocated for conventional and desmoplastic variants of ameloblastoma. The unicystic type requires additional subtyping to determine the best treatment approach.
Ameloblastoma carries a certain risk of developing local recurrences depending on histology and the type of surgical treatment.  Long-term follow-up is advised in such cases.
| Conclusion|| |
Hybrid ameloblastoma is a variation of ameloblastoma presenting distinguishable clinical, radiological, and histological features as compared with conventional ameloblastoma.
A unicystic ameloblastoma developing into a hybrid lesion is a benign, locally invasive odontogenic tumor with a probable recurrence rate with an unsuitable initial therapeutic approach. When the tumor recurrence is detected, the ideal treatment method is bone resection. This can be performed by either marginal or segmental resection depending on location and extent of recurrence.
Most cases of this rare variant of ameloblastoma need to be retrospectively analyzed to categorically explain their behavior, aggressiveness, and prognosis. The diagnosed and treated cases should be kept under regular follow-up to rule out any evidence of recurrence and malignant transformation.
This reported case reinforces that patients presenting with hybrid odontogenic lesions of this grade should undergo close follow-up for few decades after surgical treatment.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]