Unicystic Ameloblastoma of the Mandible

INTRODUCTION

Ameloblastoma develops from epithelial cellular elements and dental tissues in their various phases of development. It is a slow-growing, persistent, and locally aggressive neoplasm of epithelial origin. It is the second most common odontogenic neoplasm. The tumor is often asymptomatic presenting as slowly enlarging facial swelling. It is often associated with an unerupted third molar². It may be detected during the course of routine radiography. The vast majority of ameloblastomas arise in the mandible, and the majority of these are found in the angle and ramus region. There are three forms of ameloblastomas, namely multicystic, peripheral, and unicystic tumors³. Multicystic ameloblastoma is the most common variety and represents 86% of cases. Peripheral tumors are odontogenic tumors, with the histological characteristics of intraosseous ameloblastoma that occur solely in the soft tissues covering the tooth-bearing areas of the jaws. Unicystic tumors include those that have been variously referred to as mural ameloblastomas, luminal ameloblastomas, and ameloblastomas arising in dentigerous cysts⁴. Various treatment methods for the lesion in relation to many factors, such as the tumour size and location, have been suggested. These include enucleation, marginal resection and aggressive resection. When a diagnosis of ameloblastoma is obtained, the treatment must be aggressive and radical. The goal of treatment of ameloblastoma is to achieve complete excision and appropriate reconstruction. We present a case of a large unicystic mandibular ameloblastoma in a 30 year old female.

CASE REPORT

A 30 year old female came with a chief complaint of a slowly growing swelling on the right side of the face since one year (Figure1). Initially, the swelling was small in size but has gradually increased over a period of time to attain the present size. It was not associated with pain or difficulty in opening the mouth, chewing or articulating (Figure2). No abnormality was detected upon systemic examination. On inspection, a diffuse swelling measuring approximately 7x4 cms in size is present on the right side of face extending anteroposteriorly 2 cms from the symphisis mentii to the ramus of mandible and superoinferiorly from alatragal line to

the inferior border of mandible. The surrounding oral mucosa was normal. On palpation, the inspection findings were confirmed. The swelling was non tender and hard in consistency. The lymph nodes were non palpable. An orthopantomogram (OPG) was done, which showed large cystic lesion in the right side of mandible. The patient was taken up for enucleation and marsupialisation (Figure3) and after that for surgery under general anaesthesia (Figure 4, 5). A segmental mandibulectomy was done (Figure 6) and reconstruction plate was put (Figure7). The resected specimen (Figure 11, 12) was sent for histopathological examination and it revealed features consistent with that of the unilocular ameloblastoma.

DISCUSSION

Unicystic ameloblastoma, a variant of ameloblastoma was first described by Robinson and Martinez⁵ .Unilocular ameloblastoma is a rare type of ameloblastoma, accounting for about 6% of ameloblastomas. It usually occurs in a younger age group, with about 50% of the cases occurring in the second decade of life. More than 90% are located in the mandible^6-8. Between 50 and 80% of cases are associated with tooth impaction, the mandibular third molar being most often involved. Patients most commonly present with swelling and facial asymmetry, pain being an occasional presenting symptom. Mucosal ulceration is rare, but may be caused by continued growth of the tumor. Small lesions are sometimes discovered more on routine radiographic screening examinations or as a result of local effects (like tooth mobility, occlusal alterations and failure of eruption of teeth) produced by the tumor⁹. Histologically, the minimum criterion for diagnosing a lesion as Unilocular ameloblastoma is the demonstration of a single cystic sac lined by odontogenic (ameloblastomatous) epithelium often seen only in focal areas. Unilocular ameloblastoma should be differentiated from odontogenic cysts because the former has a higher rate of recurrence than the latter¹⁰ According to Reichart relative frequency has been reported as between 5% and 22% of all subtypes of ameloblastomas. No data is available concerning prevalence and incidence of unicystic ameloblastoma. There have been many debates regarding whether unicystic ameloblastoma develops or arises in an existing cyst¹¹. 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. ¹² .It often involves an impacted tooth and the focal area of the cystic tumor lining is often composed of a nonspecific, thin epithelium that mimics the dentigerous cyst lining.¹³ In the present case the association with an impacted tooth and presence of non specific thin epithelium lining in focal areas of cystic tumor supporting the second hypothesis i.e. arising from preexisting dentigerous cyst. Based on the character and extent of tumor cell proliferation within the cyst wall, several histologic subtypes of unicystic ameloblastoma are recognized, which include simple cystic type, intraluminal and mural type. Gardner in 1984 has pointed out that there is a difference in biological behaviour between these lesions¹⁴. Till now no recurrence has been seen and patient is still regularly being followed up. Perhaps the most important consideration regarding unicystic ameloblastoma is that of biologic behaviour. It has been widely stated that these lesions are less aggressive than their solid or multicystic counterparts and should be treated by enucleation or curettage. However, Gardner has pointed out that there is a difference in biological behaviour between those lesions that are simply cystic or show intraluminal proliferation and those in which the epithelium penetrated and breaches the fibrous wall, therefore having the capacity to invade the cancellous bone. It has been suggested that recurrence following conservative surgery is more likely to occur in the third group therefore these lesions should be treated in the same manner as solid ameloblastomas.¹⁵ Whatever surgical approach the surgeon decides to take, long-term follow-up is mandatory, as recurrence of unicystic ameloblastoma may be long delayed .¹⁶

CONCLUSION

Unicystic ameloblastoma is a tumor with a strong propensity for recurrence, especially when the ameloblastic focus penetrates the adjacent tissue from the wall of the cyst. The ability to predict this potential occurrence prior to surgery would greatly enhance therapeutic strategies for reducing the incidence. Hence, the Pathologist should examine the tissue sections carefully in an attempt to determine whether ameloblastoma has penetrated the wall of the cyst or not so that the complications can be minimized.

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