Ameloblastoma Case Study

Ameloblastoma is the most common odontogenic epithelial tumor of the jaw bones. [REF] It was first described by Churchill in 1881 and defined by Robinson as a tumor that is usually “unicentric, nonfunctional, intermittent in growth, anatomically benign, and clinically persistent”.[M] Although most ameloblastomas are histologically benign and lack cytological atypia, they are generally considered to be locally aggressive and destructive, exhibiting various rates of recurrence. Ameloblastoma Case Study. [K] WHO describes four variants of ameloblastoma, i.e. solid multicystic- follicular, plexiform, desmoplastic and unicystic. [Ref] However, many unusual histological variants have been reported in the past that mimic the conventional ameloblastomas but present with a widely variable histological presentation. Only few cases of such histological variants though have been reported in the literature which has made it difficult to predict the clinical course and biological behaviour of these variants. Here, we report a case of verrucopapillary ameloblastoma which is a very uncommon histopathological variant of ameloblastoma.

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Case report:

An 18 year old male patient reported with a chief complaint of swelling in the right side of the lower jaw near the body of the mandible since 3 months which was visible on extraorally. The swelling was hard in consistency and was not associated with pain, paresthesia or discharge. The loco-regional lymph nodes were not palpable. On intraoral examination, the overlying mucosa showed swelling in the right buccal vestibular region without any signs of ulceration or paresthesia. The teeth in the region showed positive response to stimulus on vitality testing. The panoramic radiograph showed a lytic lesion with well defined margins in the premolar–molar region extending distal to the mandibular right second molar. The orthopantomograph of the patient showed a radiolucent multilocular osteolytic lesion extending from the distal periradicular area of 43 till right posterior body angle region corresponding to mesial crown outline of 48 antero-posteriorly and from the alveolar crest till the inferior mandibular cortex supero-inferiorly. Ameloblastoma Case Study. The 3D cone beam computed tomography reconstruction showed a lesion measuring 5.9cm x 3.2cm x 2.7cm in size with fine curved and linear bony septae in the centre of the osteolytic area. The lesion was expansile with perforation of the buccal and lingual cortical plates and thinning of the inferior border of the mandible. The histopathological examination of the submitted specimen showed an unencapsulated lesion with mature fibrocellular stroma with proliferating odontogenic islands. The periphery of the tumour showed cystic cavity lined by hyperkeratinizing stratified squamous epithelium of varying thickeness. The lining epithelium was thrown into multiple sharp or blunt and rounded verrucopapillary projections into the cystic lumen plugged by keratin. These projections were supported by thin connective tissue cores. Keratin was seen deposited on the surface in the form of parallel lamella and keratin flakes were also present. An unusual finding seen in our case was the presence of acantholytic cells with areas of focal necrosis on the surfa. The lining epithelium shows basal layer with columnar cells with hyperchromatic nuclei and peripheral palisading with surface keratinization and cellular vacuolization indicative of KCOT like areas. Multiple odontogenic islands with peripheral columnar odontogenic cells with hyperchromatic nuclei were present in the connectice tissue stroma. The suppoting connective tissue stroma showed epithelial islands with acanthomatous changes and microcystic degeneration. Interconnecting strands of odontogenic epithelium resembling the plexiform variant were also present. The connective tissue was densely fibrocellular with numerous dilated and engorged blood vessels. Ameloblastoma Case Study. Immunohistochemical staining with Ki-67 antibody showed intense positivity in the basal and supra-basal cells with infrequent positivity in the superficial cells indicative of high proliferative potential of the lesion. Immunohistichemical staining with anti-p53 antibody showed basal and suprabasal positivity of the lining epithelium suggestive of mutation in the tumour suppressor gene. Based on the histopathologic evaluation, a diagnosis of papilliferous keratoameloblastoma was given. The lesion was removed completely with wide excision and the patient has not reported back with any recurrence two after the surgery.

Discussion:

Ameloblastomas are common odontogenic tumour that show diverse, yet pathognomic histopathological features. However, wide variation has been reported in the past regarding the histopathological presentation of ameloblastoma. Squamous metaplasia has been reported commonly in the acanthomatous variant of ameloblastoma where the central stellate reticulum like areas are replaced by squamoid cells. This keratinization is well documented in some lesions such as odontogenic keratocyst, acanthomatous ameloblastoma, calcifying odontogenic cyst, squamous odontogenic tumor, and squamous odontogenic carcinoma. [G] Keratin formation has also been reported in another variant of ameloblastoma termed keratoameloblastoma, which was first described by Pindborg in 1970. Another variant of keratoameloblastoma, with verrucopapillary projections into the lumen has been reported under the name papilliferous ameloblastoma. Till date, 15 cases have reported in English literature with papilliferous histologic components in ameloblastoma. [F] Ameloblastoma Case Study.

The distinction between acanthomatous ameloblastoma with keratin production and keratoameloblastoma is not clear. WHO in 2005 described keratin with pearl formation in ameloblastoma under the histologic variant of acanthomatous ameloblastoma. In 1992 classification of odontogenic tumours by WHO, it was defined as ameloblastoma with extensive keratinization. [G] However, Morgan et al have described ameloblastoma with unequivocal keratinization occurring in the centre of the epithelial follicles at the expense of the stellate reticulum-like areas as a keratoameloblastoma. Norval et al suggested that keratoameloblastoma should be considered a variant of acanthomatous ameloblastoma.[F]

However, one criteria to distinguish acanthomatous ameloblastoma form keratoameloblastoma is the presence of keratin in the connective tissue stroma as compared to acanthomatous ameloblastoma which has keratin only in the areas showing sqauamous metaplasia in the centre of odontogenic islands and follicle. [H, cross ref 7]

The present case in a male patient in the right mandibular body region is similar in presentation as compared to previously reported cases except the age of the patient which is comparatively younger (second decade) as compared to mean age of presentation of KA with papilliferous proliferation which occur at a relatively older age (mean age of occurrence in sixth decade). The right side of the mandible is commonly involved as compared to the left (2:1) with most cases reported in the posterior body-ramus region. [H] Our case differs from the previous cases in showing multiple papilliferous projections with acantholytic cells with necrotic and hemorrhagic material in the lumen and dilated, congested blood vessels. Ameloblastoma Case Study. The lesion also showed multiple solid islands of odontogenic epithelium with hyperchromatic nuclei in the connective tissue stroma.[H]

Whitt et al have described 4 variants of ameloblastoma showing keratin formation (Table 1). Corio et al.20 have described a keratinizing ameloblastic carcinoma showing the typical histologic features of malignancy in their series of ameloblastic carcinomas, which included pleomorphism, increased nuclear/cytoplastic ratio, nuclear hyperchromatism, increased numbers of mitotic figures, abnormal mitotic figures, and necrosis. Our case fulfils the criteria of papilliferous type of KA.

The present case exhibited an elevated level of mitotic activity, altered p53 profile and proliferation index (Ki-67). It can be inferred that the lesion is comparatively more aggressive locally as compared to conventional ameloblastoma, and should be excised extensively to avoid local recurrence. [F] However, it is still unclear how the production of keratin in histopathologic variants of ameloblastoma affects the biological behaviour and prognosis of such lesions. The probable reason could be attributed to less number of reported cases with follow up of such variant to comment definitively on its behaviour. [G]

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Conclusion:

Papilliferous keratoameloblastomas refers to a variant of ameloblastoma that is rarely reported and its biological behaviour is poorly understood. The present case shows higher proliferative activity in the basal and suprabasal cells of the tumour providing an indication of its local aggressiveness as compared to the conventional ameloblastomas. Ameloblastoma Case Study. Presently, such lesions are treated in a manner similar to conventional ameloblastomas, though it lacks any authoritative evidence. Report of more such cases with longer follow up duration and molecular profiling is required in the future to completely understand the spectrum of clinical and histological features, biological behaviour and prognosis of such cases.

Table 1 : Types Of Keratoameloblastoma Based On Histopathological Features(Whitt et al)

Ameloblastoma Case Study