|Year : 2008 | Volume
| Issue : 2 | Page : 65-70
Unicystic ameloblastoma: 3 case reports and review of literature
Simi Thankappan1, Valsa Thomas1, Sharafudeen Kandamparambil1, Sherin Nair2
1 Department of Oral Medicine and Radiology, Government Dental College, Calicut, India
2 Department of Oral Pathology and Microbiology, Government Dental College, Calicut, India
Post graduate Student, Department of Oral Medicine & Radiology, Government Dental College, Calicut -673008, Kerala
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The term unicystic ameloblastoma (UA) refers to those cystic lesions that show clinical, radiographic, or gross features of a jaw cyst, but on histologic examination show a typical ameloblastomatous epithelium lining part of the cyst cavity, with or without luminal and/or mural tumor growth. Even though the lesion is not as aggressive as the solid ameloblastoma, an accurate histopathologic diagnosis is essential for the treatment and prognosis. Here we present 3 cases of UA showing different histologic features and coming under histologic variants of UA. These cases re-establish the fact that thorough microscopic examination of the surgical specimen is necessary for the final diagnosis of UA. Also the complexity of the diagnostic process of bone pathologies increases when the lesions are present at uncommon locations. The most important aspect governing treatment modalities in these three cases are individual considerations rather than theoretical factors.
Keywords: Unicystic ameloblastoma, intraluminal, mural, plexiform
|How to cite this article:|
Thankappan S, Thomas V, Kandamparambil S, Nair S. Unicystic ameloblastoma: 3 case reports and review of literature. J Indian Acad Oral Med Radiol 2008;20:65-70
|How to cite this URL:|
Thankappan S, Thomas V, Kandamparambil S, Nair S. Unicystic ameloblastoma: 3 case reports and review of literature. J Indian Acad Oral Med Radiol [serial online] 2008 [cited 2020 Sep 20];20:65-70. Available from: http://www.jiaomr.in/text.asp?2008/20/2/65/44368
| Introduction|| |
The term unicystic ameloblastoma (UA) refers to those cystic lesions that show clinical, radiographic, or gross features of a jaw cyst, but on histologic examination show a typical ameloblastomatous epithelium lining part of the cyst cavity, with or without luminal and/or mural tumor growth. 
The term 'Unicystic Ameloblastoma' was adopted in the second edition of the international histologic classification of odontogenic tumors. Unicystic ameloblastoma was first described by Robinson and Martinez in 1977.  It accounts for 10-15% of all intraosseous ameloblastomas.  The term 'unicystic ameloblastoma' is derived from the macro- and microscopic appearance, the lesion being a well defined, often large monocystic cavity with a lining, focally but rarely entirely composed of odontogenic (ameloblastomatous epithelium). It is often accompanied by an innocuous epithelium of varying histologic appearance that may mimic the lining of a dentigerous or radicular cyst. 
There can be three pathologic mechanisms for the evolution of UA: 
- The reduced enamel epithelium associated with the developing tooth undergoes ameloblastic change with subsequent cystic transformation.
- Ameloblastomas arise in dentigerous or other types of odontogenic cysts in which the neoplastic ameloblastic epithelium is preceded temporarily by a non-neoplastic stratified squamous lining.
- Solid ameloblastoma undergoing cystic degeneration of ameloblastic islands with subsequent fusion of multiple microcysts and then into a unicystic lesion.
| Case Report|| |
An 11-year old girl was referred to Government Dental College, Calicut with a swelling on the right side of the face. It started as a small swelling 2 months back and enlarged to its present size. Because of lack of relief after consultation with a dentist, she was referred to Dental College. At the time of presentation, there was a diffuse swelling lateral to the ala of nose and intraorally involved both labial and palatal sides of 11, 12, 13, 14 and 15 with tipping of 12 and 13 [Figure 1]. It was about 3×2 cm. There was no history of pain, toothache, pus discharge or paresthesia. Cystic fluctuancy was present on palatal aspect of swelling. A provisional diagnosis of odontogenic cyst was made on clinical findings.
On radiographic examination, periapical and the occlusal radiographs showed a well defined radiolucency of size 4×2 cm extending from 11-15. The lateral incisor had an open apex with dens- in- dente extending up to the middle third of the root [Figure 2]. Detailed analysis of the image revealed an interrupted lamina dura on the root apex. Computerized tomography scan showed an expansile radiolucency in the region suggestive of odontogenic cyst [Figure 3]. Aspiration yielded a straw colored fluid with abundant cholesterol crystals. Vitality tests showed vital 11 and nonvital 12, 13, 14, 15. A working diagnosis of periapical cyst due to dens in dente of 12 was made.
Enucleation was planned based on the diagnosis of a periapical cyst. The lesion was completely removed and the radiographic image of an encapsulated cystic lesion was confirmed during surgery. Contrary to the most probable clinical diagnosis, i.e . , periapical cyst, microscopic analysis of the surgical specimen revealed simple UA [Figure 4]. The nonvital teeth were endodontically treated. The patient is under strict follow up.
A 27 year old patient reported to Oral Medicine department with complaint of occasional bleeding from posterior part of left lower jaw since two months. There was no extraoral swelling, no history of pain, toothache, pus discharge or paresthesia. On intraoral examination, a mild swelling with slight fluctuance was noted in the posterior region distal to 37 and medial to ramus. 38 was missing and there was no history of extraction. A clinical diagnosis of odontogenic cyst of 38 was made.
On radiographic examination, panoramic view showed a well defined multilocular radiolucency of size 8×4 cm distal to 37 with impacted 38 displaced and lying close to the lower border of the mandible [Figure 5]. Anteriorly the radiolucency started from distal aspect of 37, extending postero-superiorly up to the subcondylar region with complete resorption of coronoid process. The lesion involved the entire thickness of ramus in the upper and middle part; up to 1 cm from the angle of mandible. The lesion had almost pushed 38 to the lower border. Sclerotic border was present in the most superior region. CT showed a well defined expansile lytic lesion with no marginal sclerosis or periosteal reactions. The report was suggestive of dentigerous cyst with differential diagnosis as ameloblastoma [Figure 6]. Aspiration yielded blood. A working diagnosis of ameloblastoma was made on the basis of clinical and radiographic findings.
Incision biopsy showed features of plexiform UA. Even though the patient was young, a conservative treatment was not possible because of extensive involvement of both coronoid and condyle. Part of the mandible with the lesion was resected under general anesthesia and the defect was reconstructed using iliac graft.
Gross specimens showed a cystic capsule in the lower half of ramus enclosing impacted third molar and intraluminal tumor in upper ramus. The histopathology report was confirmatory of plexiform UA [Figure 7]. The patient is currently under follow up and no recurrence has been reported so far.
An 18-year old male presented to Oral Medicine department with painless swelling of 6-months duration over right mandibular posterior region. The patient reported that the swelling had gradually increased in size over a period of 6 months. There was no history of pain, pus discharge, toothache or paresthesia. Clinical examination revealed a bony hard swelling over the right side of mandibular molar-ramus region. Intraoral examination showed buccal cortical plate expansion in the third molar region. There was no fluctuancy related to the swelling. 48 was missing and there was no history of extraction. A clinical diagnosis of odontogenic cyst / tumor was made.
On radiographic examination, panoramic radiograph showed a unilocular radiolucent lesion of size 5×4 cm extending from 47 to the mid ramus region, with 48 embedded in the lesion [Figure 8]. CT scan showed a unilocular expansile lytic lesion with minimal extension of solid components into the adjacent soft tissue with third molar in the lesion. Report was suggestive of ameloblastoma [Figure 9]. Aspiration yielded blood. A working diagnosis of ameloblastoma was made on the basis of clinical and radiographic findings.
An incision biopsy was done. Histopathologically the lesion was characterized as a mural ameloblastoma [Figure 10]. Considering the patient's age and the size of the lesion, a conservative treatment plan was adopted. The lesion was enucleated and chemical cauterization with Carnoy's solution was done under GA along with extraction of 47 and 48. The patient is under strict follow up and no recurrence has been reported so far.
| Discussion|| |
The ameloblastoma is a true neoplasm of odontogenic epithelial origin. It is the second most common odontogenic neoplasm, and only odontoma outnumbers it in reported frequency of occurrence.  Its incidence, combined with its clinical behavior, makes ameloblastoma the most significant odontogenic neoplasm.
Ameloblastoma, according to the new classification approved at the Editorial and Consensus Conference held in Lyon, France in July 2003 in conjunction with the preparation of the new WHO Blue Book volume 'Pathology and Genetics of Tumors of the Head and Neck' is included under "benign neoplasms and tumor-like lesions arising from the odontogenic apparatus showing odontogenic epithelium with mature fibrous stroma, without ectomesenchyme" and is divided into four types. 
- The classic solid/multicystic ameloblastoma (SMA)
- The UA
- The peripheral ameloblastoma (PA)
- The desmoplastic ameloblastoma (DA), including the so-called hybrid lesions.
Some of the terms used for UA prior to 1977 were cystic ameloblastoma, ameloblastoma associated with dentigerous cyst, cystogenic ameloblastoma, extensive dentigerous cyst with intracystic ameloblastic papilloma, mural ameloblastoma, dentigerous cyst with ameloblastomatous proliferation and ameloblastoma developing in a radicular cyst. 
The UA occurs in a younger age group, with slightly more than 50% of cases occurring in patients in the second decade of life. In more than 90% of cases, the UA is located in the mandible, with 77% located in the molar ramus region (mandible to maxilla 13:1). ,, Between 50 and 80% of cases are associated with tooth impaction, the mandibular third molar being most often involved. The 'dentigerous' type occurs on average 8 years earlier than the 'non-dentigerous' variant. The mean age for unilocular, impaction-associated UAs is 22 years, whereas the mean age for the multilocular lesion unrelated to an impacted tooth is 33 years.  There are no reports of any sexual or racial predilection. , UA dentigerous variant may show a slight male predilection while this ratio is reversed in cases of UA not associated with impacted tooth. 
Patients most commonly present with chief complaints of swelling and facial asymmetry. Although the swelling is typically asymptomatic, pain is an occasional presenting sign. A chief complaint of painless swelling often indicates a lesion of long duration and significant size. Continued growth of the tumor and enlargement of the involved area may eventuate in ulceration of the mucosa overlying the lesion. Small lesions tend to be discovered more often on routine radiographic screening examinations or as a result of local effects produced by the tumor. Such local effects include tooth mobility, occlusal alterations and failure of eruption of teeth. 
Maxillary UAs are very rare. The first case reported by Gardner and colleagues in 1987 occurred in a 12 year old boy in the molar area. There was no bone infiltration.  UA in the anterior maxilla is considered to be rare and atypical. 
Radiograph of UA presents with unilocular and multilocular patterns with clear predominance for unilocular configuration. Unilocular pattern is often misdiagnosed as an odontogenic keratocyst or Keratinizing Cystic Odontogenic Tumor  (KCOT) or a dentigerous cyst and is seen in cases associated with tooth impaction. However, it is stressed that although the lesion is pathomorphologically unicystic, it will far from always produce a unilocular radiolucency. Eversole et al. were able to identify six radiographic patterns for UA ranging from well defined unilocular to multilocular appearances. 
Truly multilocular UAs are not encountered often. The scalloping of the cortex and differential bone loss also produces the illusion of a multilocular process on the plane films. The scalloping resorption of the cortical plates rather than compartmentalized areas separated by true bony septa can be visualized in CT images.  Contrast-enhanced magnetic resonance imaging was considered useful in the diagnosis of UA, as characteristic features of this type of lesion i.e., thick enhancement of the tumor wall and small intraluminal nodules were detected only by CE-MRI. 
Histologically, the minimum criterion for diagnosing a lesion as UA is the demonstration of a single cystic sac lined by odontogenic (ameloblastomatous) epithelium often seen only in focal areas. UA should be differentiated from odontogenic cysts because the former has a higher rate of recurrence than the latter.  In a clinicopathologic study of 57 cases of unicystic ameloblastoma, Ackermann et al . classified this entity into 3 histologic groups. 
Group I: - Luminal UA (tumor confined to the luminal surface of the cyst).
Group II: - Intraluminal/Plexiform UA (nodular proliferation into the lumen without infiltration of tumor cells into the connective tissue wall).
Group III: - Mural UA (invasive islands of ameloblastomatous epithelium in the connective tissue wall not involving the entire epithelium).
Histologic subgrouping (modified after Ackermann et al .) by Philipsen and Reichart. 
Subgroup 1 - Luminal UA
Subgroup 1.2 - Luminal and intraluminal
Subgroup 1.2.3 - Luminal, intraluminal and intramural
Subgroup 1.3 - Luminal and intramural
Plexiform UA, the histologic equivalent of intraluminal UA and coined by Gardner  refers to a pattern of epithelial proliferation that has been described in dentigerous cysts. It does not exhibit the histologic criteria for ameloblastoma published by Vickers and Gorlin. , Plexiform UAs are not always associated with unerupted teeth, in which case they probably occur over a wider age range than those resembling dentigerous cysts.  It exhibits a low rate of recurrence following enucleation or curettage. 
The UAs diagnosed as subgroups 1 and 1.2 may be treated conservatively (careful enucleation), whereas subgroups 1.2.3 and 1.3 showing intramural growths must be treated radically, i.e., as a solid or multicystic ameloblastoma.  Vigorous curettage of the bone is discouraged since it may implant foci of ameloblastoma more deeply into bone. Chemical cauterization with Carnoy's solution is also advocated for subgroups 1 and 1.2. Subgroups 1.2.3 and 1.3 in which the cystic wall is involved with islands of ameloblastoma tumor cells and there is possible penetration into the surrounding cancellous bone are thought to be associated with a high risk for recurrence, requiring more aggressive surgical procedures. ,,,
Because the presence of islands of odontogenic epithelium in the cyst wall influences the surgical approach, it is recommended that pathologists carefully examine cystic ameloblastoma surgical specimens for their presence. Multiple, even serial sections are required for examinations. The true nature of these lesions becomes evident only when the entire specimen is submitted for microscopy. The pathology report should include a description of the islands with an indication of their site in the capsule of the tumor. Also treatment plan should take into account factors like individual patient considerations, clinical judgment of the surgeon, type of jaw involved and whether recurrence has occurred or not.
Average interval of recurrence is 7 years. Recurrence is also related to histologic subtypes of UA, with those invading the fibrous wall having a rate of 35.7%, but others only 6.7%. 
Recurrence rates were 3.6% for resection, 30.5% for enucleation alone, 16% for enucleation followed by Carnoy's solution application, and 18% by marsupialization followed by enucleation (where the lesion reduced in size) or resection. 
Three cases of UAs are presented with review of literature highlighting histologic variants and mode of treatment.
First case presented, is a subgroup 1 lesion with no infiltration into the surrounding bone. Fortunately, the surgical conduct was compatible with the biological nature of unicystic ameloblastoma, which does not present an aggressive clinical behavior. In addition, scrupulous review of the surgical specimen revealed the absence of ameloblastic cell chains infiltrating the fibrous capsule, indicating a good prognosis and low recurrence potential. This case illustrates the obvious need for meticulous histologic examination of every cystic lesion of the jaw.
Case two may be treated as a subgroup 1.2 UA. This is the most common presentation of UA. Even though the treatment for this type is theoretically enucleation and curettage, because of the extensive size of the lesion, resection of affected side of mandible was done.
The third case falls under subgroup 1.3 lesions which are usually treated radically. Here conservative management using enucleation and chemical cauterization with Carnoy's solution was done under general anaesthesia.
Despite the fact that UA may, in general, compare favorably with its solid or multicystic counterpart in terms of clinical behavior and response to treatment, the tumors containing invading islands in the fibrous wall could have a high risk of recurrence. The treatment should be in correlation with the histologic and clinical behavior of the lesion. Furthermore, recurrence of UA may be long delayed, and a long-term postoperative follow up is essential to the proper management of these patients. Although the histologic pattern may have implication for the likelihood of recurrence, it should not affect treatment decision. The growth pattern, the jaw in which the tumor is found, age of the patient and histopathologic subtypes are the most important factors when considering treatment options.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]