Ameloblastoma is a benign, slowly growing, locally invasive, epithelial odontogenic tumour of the jaws with a high rate of recurrence if not completely excised. It is classified into solid/multicystic, extraosseous/peripheral, desmoplastic and unicystic types . Unicystic ameloblastoma is an infrequent variant and accounts for 5 - 15% of all ameloblastomas . The mean ages are 16 and 35 years for unerupted and erupted tooth respectively . Vast majority of cases present as painless swelling with facial asymmetry . Radiologically, it presents as a well corticated unilocular radiolucency . The unicystic ameloblastoma is further subdivided into two basic histopathological patterns, the luminal and mural . The treatment depend on clinico-pathological factors such as the size, anatomical site and histologic variant . There is paucity of reports on unicystic ameloblastoma in our setting. We are presenting a case of unicystic ameloblastoma in a 17-year old female.
A 17-year old female attended the Maxillofacial surgery outpatient clinic with four years history of painless frontal lower jaw swelling. There was no history of paraesthesia, bleeding, discharge of fluid or pus from this gradually increasing swelling. Past dental history was not contributory as the patient had never visited a dental clinic previously. So also the past medical history. Physical examination revealed a well circumscribed swelling in the anterior mandible extending from first premolar on the right to the first premolar on the left mandible (Figure 1). The swelling measured 6cm in diameter with cortical expansion mainly of the buccal plate. The mucosa surface was pink without evidence of ulceration. There was egg crackling sensation on palpation of the buccal cortical plate. All teeth were firm except the lower right central incisor which showed grade one mobility. A golden-yellowish fluid with shimmering effect was aspirated from the lesion. Other systemic examinations were unremarkable. Xrays were requested for, which included right/left oblique laterals,occlusal and PA views. It demonstrated a well circumscribed radioluscent lesion with cortical rimming, lamina dura of the affected teeth were intact except for the root of the lower first incisor that was slightly amputated (Figure 1). Results of routine baseline investigations were essentially normal. Clinical diagnosis of dentigerous cyst, /ameloblastoma was made.
The patient was counseled and had enucleation via intraoral buccal flap approach. Portions of the lingual plates overhanging were nibbled to prevent necrosis and subsequent steomyelitis. Post operative recovery was uneventful. The enucleated lesion was submitted for histopathological examination and revealed cyst wall lined by ameloblasts exhibiting nuclei palisading, reverse polarity and subnuclear vacuoles. Foci of stellate reticulum like cells were noted and diagnosis of unicystic ameloblastoma was made (Figures 2,3). Showed the histology of unicystic ameloblastoma. The patient showed remarkable improvement without any evidence of recurrence for over four years of follow-up visits.
Unicystic ameloblastoma is a rare variant of ameloblastoma, presenting as a cyst.It accounts for 5 - 15% of all ameloblastomas and there are many debates concerning the origin of unicystic ameloblastoma whether it arises de novo or from non-neoplastic cyst epithelium . Leider et al, proposed three pathogenic mechanisms for the evolution of unicystic ameloblastoma: reduced enamel epithelium, from dentigerous cyst and due to cystic degeneration of solid ameloblastoma . It often involves an impacted tooth and the focal area of the cystic tumour lining is often composed of a non specific, thin epithelium that mimics the dentigerous cyst lining . The origin of the index case is not clear.
Unicystic ameloblastoma tends to affect young patients, with about half of cases occurring in the second decade of life . The index case is a 17-year old female. Mandible is the common site of involvement in more than 90% of cases, usually the posterior region . This is in contrast with the present case which was found in the anterior mandible. Majority of cases are asymptomatic, sometimes presenting as painless swelling of the jaws as seen in our case. Atimes, it may grow and causes mucosa ulceration. Small cysts are usually detected by routine radiographs or due to local effects of the lesion Radiological examination is vital in making diagnosis and planning for surgery. It presents as a well corticated unilocular radiolucency. Root resorption can be seen.4 The index case showed a well circumscribed radioluscent lesion with cortical rimming suspected to be a dentigerous cyst. Dentigerous cysts are mostly seen in panoramic radiographies as unilocular, welldefined radiolucent areas that show cortication. Inaddition, dentigerous cyst may resemble odontogenic keratocyst and ameloblastic fibroma on plain radiography. Odontogenic keratocysts are not always pericoronal. They cause less expansion and less root resorption. Ameloblastic fibromas are expansive unilocular or multilocular radiolucencies that are well-defined, corticated border and mostly they do not have tooth structure or calcification within the lesion. In many cases, they are associated with the crown of an unerupted tooth. Computed tomography (CT) provide important information for the differential diagnosis .
The definitive diagnosis is based on histopathological examination. It is divided into luminal and mural type. In luminal variant, the tumour is confined to the luminal surface. The present case show no evidence of tumour infiltration within the fibrous wall. Whereas in the mural variant, there are invasive islands of ameloblastomatous epithelium within the fibrous wall. Dentigerous cyst are usually lined by stratified squamous epithelium . Average interval of recurrence is 7 years. Recurrence is also related to histologic subtypes of unicystic ameloblastoma, with those invading the fibrous wall having a rate of 35.7%, but others only 6.7% . The index patient had no evidence of recurrence for over four years of follow-up visit. Long-term follow-up is necessary because of occasional cases of delay recurrence of unicystic ameloblatoma .
Unicystic ameloblastoma involving anterior mandible is rare, meticulous observation, high index of suspicion, radiological and histopathological features are essential in making challenging diagnosis.
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