Hybrid ameloblastoma: An amalgam of rare and conventional ameloblastoma.

Ameloblastoma is a common benign odontogenic tumor with multiple histologic types. This case report describes an unusual type of ameloblastoma called "Hybrid Ameloblastoma" with features of both follicular and desmoplastic ameloblastoma in a 50-year-old female. This is a very rare form of ameloblastoma as <30 cases have been reported so far in literature. Though this rare form of ameloblastoma is only a histologic variant, it poses a great challenge to diagnosticians and thus to surgeons as there will be mismatch of biopsy reports at different sites in the same tumor thereby changing the treatment plan. This case report is one such example of diverse presentation of this ameloblastoma with conflicting histopathological diagnosis at initial biopsy and on surgical excision.

Introduction

Ameloblastoma is a common benign but locally aggressive neoplasm of odontogenic origin. It accounts for about 18% of the various odontogenic neoplasms.[12] It is known to occur in many forms. In 2005, the World Health Organization histologically classified the ameloblastoma into (1) solid/multicystic, (2) extra-osseous/peripheral, (3) desmoplastic, and (4) unicystic. The solid/multicystic ameloblastoma was further divided into a follicular and a plexiform type. The follicular type has 4 subtypes - a spindle cell type, an acanthomatous type, a granular type, and a basal cell type.[3]

The prevalence of solid/multicystic variant of ameloblastoma ranges from 11% to 95.4%; whereas that of other variants such as peripheral, desmoplastic, and unicystic range between 2–10%, 4–13%, and 5–22% of all ameloblastomas, respectively.[4]

Waldron and El-Mofty discovered a rare variant of ameloblastoma composed histologically of areas of the classic follicular or plexiform ameloblastoma and areas of desmoplastic ameloblastoma. This was named hybrid ameloblastoma (HA). To best of our knowledge, <30 cases of hybrid variant of desmoplastic ameloblastoma have been published so far.[5] The aim of this article is to report one such rare case for better understanding of this ameloblastic variety which could pose difficulty in diagnosis and treatment due to its diverse histopathological presentation.

Case Report

A 50-year-old female reported to the Department of Oral Medicine and Radiology, Manipal College of Dental Sciences, Manipal, India, with the complaint of asymptomatic swelling in the right side of lower jaw since 1 year. Swelling started spontaneously and enlarged slowly to the present size. She did not report of any pain/trauma/sinus opening/bleeding/or any altered sensation in that region. She had no contributory medical history.

There were no abnormal findings in physical and extra oral examination with no gross facial asymmetry and no abnormality on the visible skin surfaces and scalp. However, on palpation, there was a slight bony hard bulge felt in the right body of mandible.

Intra oral examination revealed a single rounded swelling on the buccal aspect of 44, and 45 approximately 2 cm × 2 cm obliterating the buccal sulcus with normal overlying mucosa [Figure 1]. The teeth in that region showed no evidence of caries.

Figure 1

Intra oral picture showing buccal cortical expansion

On palpation, there was bony hard, nontender expansion of buccal cortex w.r.t 44 and 45 with no lingual cortical involvement. Associated teeth 44, 45 were vital with no mobility and 43, 46 were missing.

The long duration of the swelling, its asymptomatic nature and absence of odontogenic abnormalities raised the suspicion of a benign bony lesion - odontogenic cyst/tumor was considered in the clinical differential diagnosis.

A screening panoramic radiograph [Figure 2] showed a large multilocular radiolucency extending from distal border of lower right lateral incisor to 1st molar region approximately 4 cm and superioinferiorly 3 cm. The lesion was well defined with corticated borders and multiple thick radiopaque septae giving it the characteristic “soap bubble” appearance.

Figure 2

Panoramic radiograph showing “soap bubble” appearance of the tumor

Computed tomography scan revealed a multiloculated, expansile, well demarcated lytic lesion in the body of the right hemi mandible involving the alveolar process of canine and first premolar, eroding through cortex into adjacent soft tissues with no evidence of periosteal reaction.

Radiographic features of multilocular radiolucency in the mandibular molar region not crossing the midline with thick radiopaque septae and buccolingual expansion, favored diagnosis of ameloblastoma.

A bone biopsy of the region was done under local anesthesia. Histopathological examination revealed small strands of cords of tumor cells with cubical odontogenic epithelium and peripheral ameloblasts and stellate reticulum-like cells that exhibited squamous metaplasia at places. The intervening stroma was dense and collagenous exhibiting desmoplasia and compressing the odontogenic epithelial cells. These features were suggestive of desmoplastic ameloblastoma [Figure 3].

Figure 3

Pictomicrograph depicting small cords of tumor cells with peripheral ameloblast like cells and stellate reticulum like cells that exhibit squamous metaplasia at places

A wide segmental resection by maintaining lower border continuity was planned for the patient. After segmental resection of the right body of the mandible, the gross specimen was again sent for histopathological examination. The histopathology report of the resected specimen was different from the presurgery biopsy report, which revealed a mature connective tissue stroma with follicles showing peripheral tall columnar cells with hyperchromatic nuclei with reversal of polarity. There was also dense connective tissue stroma with small nests of odontogenic epithelium. These features were suggestive of a hybrid lesion of follicular ameloblastoma with desmoplasia along with areas exhibiting cystic degeneration and squamous metaplasia [Figure 4].

Figure 4

Pictomicrograph depicting it as follicular ameloblastoma with desmoplasia along with areas exhibiting cystic degeneration and squamous metaplasia

The patient is on regular follow-up and postoperative course was uneventful. Radiographic examination of the patient after 1.5 years showed no evidence of recurrence of the lesion and the iliac graft consolidated adequately.

Discussion

Ameloblastoma is a common odontogenic tumor accounting for around 18% of all odontogenic jaw tumors. Follicular and plexiform are the most common histologic variants accounting for 32.5% and 28.2% while desmoplastic is extremely rare with incidence rates ranging from 4% to 13%. The present case showed microscopic features of both desmoplastic ameloblastoma and classic follicular ameloblastoma. It is still not clear whether desmoplastic changes occur secondarily in the stroma of a preexisting solid/multicystic variant of ameloblastoma, or whether the areas of primary desmoplastic ameloblastoma transform in to solid multicystic type.[6] Radiologically, the desmoplastic variant exhibits atypical and varied radiographic features such as: Localized irregular multilocular radiolucency with indistinct borders or a mixed radiopaque-radiolucent appearance with ill-defined margins. The features of the HA reported so far have been compiled in Table 1.[7]

Table 1

Features of 30 compiled cases of hybrid lesions of ameloblastoma

The characteristics of the case presented in this report were compared with those of the 29 cases reported in the literature. The present case matched with gender (female), site (mandibular canine-premolar region), and radiographic features of mixed radiolucent and radiopaque appearance. After a thorough literature search, we found difference of opinion regarding the surgical management since there is no established biologic behavior of this variant of ameloblastoma yet.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.