Unicystic Ameloblastoma of Mandible- Imaging Features: A Case Report and Literature Review

Abstract

Ameloblastoma are benign tumors whose importance lies in its potential to grow into enormous size with resulting bone deformity. They are typically classified as unicystic, multicystic, peripheral, and malignant subtypes. Unicystic ameloblastoma (UA) refers to those cystic lesions that show clinical, radiographic, or gross features of an odontogenic cyst but on histological examination show a typical ameloblastomatous epithelium lining, with or without luminal and/or mural tumor growth. We present a very rare case of unicystic ameloblastoma in a girl child with an age of 10 years; clinical and radiographic features of UCA, its differential diagnosis, histopathology, and current concepts of management have also been discussed in the present paper.

Keywords

Ameloblastoma - computed tomography - imaging of ameloblastoma - unicystic ameloblastoma

Introduction

Ameloblastoma is the most common benign odontogenic tumor accounting for approximately 1% of tumors and cysts of the jaw and 10% of all the odontogenic tumors.[1] It is a slow-growing, persistent, and locally aggressive neoplasm that may originate from the epithelium involved with the formation of teeth such as enamel organ, odontogenic rests of Malassez, reduced enamel epithelium, and odontogenic cyst lining.[2]

Ameloblastoma may occur centrally within the bone or peripherally, without an intraosseous component in the soft tissues overlying the alveolar ridge. Intraosseous lesions are of two types solid/conventional/multicystic and unicystic.[3] Unicystic ameloblastoma (UA), a variant of ameloblastoma first described by Robinson and Martinez[4] in 1977, refers to those cystic lesions that show clinical and radiologic characteristics of an odontogenic cyst but in histologic examination show a typical ameloblastomatous epithelium lining part of the cyst cavity with or without luminal and/or mural tumor proliferation. Before the report by Robinson and Martinez, this variant had been referred to as a mural or intraluminal ameloblastoma. Recognition of this growth pattern is very important because of its unicystic radiographic appearance, histologic findings, association with an unerupted tooth, occurrence in the mandible of younger patients, and a recurrence rate after conservative surgical treatment lower than that of its conventional counterpart.[5]

We present a case of a unicystic ameloblastoma in a 10-year-old child patient who reported with a complaint of swelling of her right lower jaw.

Case Report

A 10-year-old female child came with a complaint of swelling on the right lower side of her jaw for 1 month which was insidious in onset and got gradually progressed to the present size. It was associated with severe, intermittent, and dragging type of pain which radiates to the right ear. Pain relieved with medication. It was also associated with extraoral swelling for 15 days. On extraoral examination, facial asymmetry was seen in the right lower third of the face. On intraoral examination, a solitary diffuse swelling was seen in the buccal vestibular region of 85 and 46, extending anteroposteriorly from middle third of 85 to distal surface of 46. Superiorly the swelling of the lesion is extending from attached gingiva of 85 and 46 to inferiorly into the buccal vestibule. Sinus opening with pus discharge was seen on the attached gingiva of 85 (buccal or lingual). On palpation, swelling was tender, hard in consistency, noncompressible, and nonreducible. Expansion of buccal cortical plate was felt in relation to 85 and 46.

Based on the history and clinical examination, a provisional diagnosis of ameloblastoma was made. Under differential diagnosis, ameloblastic fibroma and odontogenic keratocyst were considered. Intaoral periapical view (IOPA), occlusal view,orthopantomogram (OPG), and computed tomography (CT) scan were taken. IOPA taken in relation to 85 and 46 [Figure 1] showed diffuse radiolucency distal to 46 with the absence of 47 tooth bud. OPG [Figure 2] view showed a solitary, well-defined radiolucency of size 3 cm × 2 cm extending anteroposteriorly from mesial root of the tooth number 46 is 1 cm from the posterior border of the ramus of the mandible, superoinferiorly 1 cm below the sigmoid notch, to the inferior border of the mandible thinning the inferior cortical margin. Internal structure was radiolucent with the displaced tooth bud of 47 in the ramus region.

Figure 1: Intraoral periapical radiograph showing diffuse radiolucency distal to 46 with the absence of 47 tooth bud

Figure 2: Preoperative orthopantomogram showing solitary, well‑defined radiolucency of size 3 cm × 2 cm surrounding the crown of 47 tooth bud which got displaced into the ramus region with thinning of the inferior border of the mandible

Panoramic CT section [Figure 3] and sagittal CT section [Figure 4] showed hypodense area of size 2.5 cm × 3 cm surrounding the developing tooth bud of 47. Axial CT section [Figure 5]a showed tooth within the hypodense area, and axial CT section [Figure 5]b showed buccal cortical plate expansion with breakdown of lingual cortical plate.

Figure 3: Panoramic computed tomography section showing complete extension of the lesion

Figure 4: Sagittal computed tomography section showing hypodense area surrounding the developing tooth bud of 47

Figure 5: (a) Axial computed tomography section showing tooth within the hypodense area (b) Axial computed tomography section showing buccal cortical plate expansion with breakdown of lingual cortical plate

An incisional biopsy was done and it showed epithelial lining with ameloblast-like cells and adjacent connective tissue stroma. There was no luminal proliferation of epithelium, suggestive of intraluminal ameloblastoma [Figure 6]. Following the diagnosis, the parents were informed about the condition and proposed treatment. Surgical enucleation along with chemical cauterization with Carnoy's solution [Figure 7] was done under general anesthesia along with extraction of 47 [Figure 8] considering age of the patient. The patient is under follow-up, with no functional or esthetic complaints. Six months posttreatment, OPG shows signs of new bone formation [Figure 9].

Figure 6: Low-power histopathological picture of unicystic ameloblastoma showing intraluminal proliferation

Figure 7: Surgical site of enucleation

Figure 8: Surgical specimen with extracted 47

Figure 9: Postoperative orthopantomogram showing signs of new bone formation

Discussion

UA accounts for 6%–15% of all intraosseous ameloblastomas.[1] It is less aggressive and usually occurs in an earlier age group than the solid or multicystic with about 50% of the cases occurring in the second decade of life. As in the present case, >90% of UA are seen affecting the mandibular region,[6] which was also seen in present case. In most cases, UA are associated with impacted tooth, mandibular third molar being the most common.[7]

The term unicystic is derived from the macroscopic and microscopic appearance, the lesion being essentially a well-defined, often large monocystic cavity with a lining, focally but rarely entirely composed of odontogenic (ameloblastomatous) epithelium.[8]

The pathogenesis of cystic ameloblastomas remains obscure. Some investigators believe that UA arises from preexisting odontogenic cysts, in particular a dentigerous cyst, while others maintain that it arises de novo. The reason why some ameloblastomas become completely cystic may be related to epithelial dysadhesion (e.g., defective desmosomes) or, more likely, to the intrinsic production of proteinases enzymes that normally degrade the central zone of the enamel organ after tooth development.[9] (e.g., metalloproteinases and serine proteinases).[9]

Radiographically, the unilocular: multilocular ratio is 13:3 when the lesion is associated with an impacted tooth. For the “nondentigerous” variant, this ratio changes to 8:7. Further, the “dentigerous” type occurs on average 8 years earlier than the “nondentigerous” variant. Finally, 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.[7]

Ackermann et al.[10] classified unicystic ameloblastoma into three types with prognostic and therapeutic implications such as:

• 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 (invasive islands of ameloblastomatous epithelium in the connective tissue wall not involving the entire epithelium).

The microscopic pattern that exhibits mural invasion in UA suggests a more aggressive potential.[11]

Another histologic subgrouping by Philipsen and Reichart[12] has also been described as follows:

• Subgroup 1: Luminal

• Subgroup 1.2: Luminal and intraluminal

• Subgroup 1.2.3: Luminal, intraluminal, and intramural

• Subgroup 1.3: Luminal and intramural.

The unicystic ameloblastomas diagnosed as subgroups 1 and 1.2 can be treated conservatively (enucleation), whereas subgroups 1.2.3 and 1.3 showing intramural growths require radical resection, as for a solid or multicystic ameloblastoma. Following enucleation, vigorous curettage of the bone should be avoided as it may implant foci of ameloblastoma deeper into bone. Chemical cauterization with Carnoy's solution[13] is also advocated for subgroups 1 and 1.2. Subgroups 1.2.3 and 1.3 have a high risk for recurrence, requiring more aggressive surgical procedures.[14]

Recurrence rates for unicystic ameloblastoma after conservative surgical treatment (curettage or enucleation) are generally reported to be <25%. For intraluminal and plexiform type of unicystic ameloblastoma, recurrence rate was found to be as low as 10.7%.[15] Recurrence rates for solid multicystic ameloblastoma was found to be about 50%–90%.

The present analysis included only publications in English. All well-documented publications during the last 20 years were collected, and several clinicopathological features of each case were studied. The following data were recorded: age (≤10 years), sex, location, clinical features/symptoms, histological type, radiographic appearance, and treatment. Only reports of unicystic ameloblastoma in children <10 years confirmed by histological analysis with all the data required for tabulation were included and the articles not having enough information were excluded [Table 1].

Table 1

English literature review till date

Year	Author	Age	Sex	Location	Clinical features	Histological features	Radiological features	Treatment
INA – Information not available; UL – Unilocular ameloblastoma
1998	Li etal.[16]	10	Female	Mandible	Mild fullness over the cheek	Unicystic ameloblastoma	UL	Enucleation
2000	Li etal.[17]	5	Male	Maxilla (premolar to second molar)	Cystic lesion	Mural type	INA	Enucleation
2003	Al-Khateeb and Ababneh[18]	9	Female	Mandible	Painless swelling	Unicystic ameloblastoma	UL	Enucleation plus peripheral ostectomy
2007	Huang et al.[19]	9	Male	Body-angle of INA the mandible	INA	UL	Enucleation and peripheral ostectomy
2008	Qureshi et al.[20]	10	Female	Mandible	Mild fullness over the cheek	Unicystic ameloblastoma	UL	Enucleation, curettage
2008	Gulten et al.[21]	8	Male	Right mandible	Painless hard swelling	Unicystic ameloblastoma	UL	Enucleation and extraction of related teeth
2011	Chacko and Kuriakose[22]	9	Male	Mandible	Pain and swelling in relation to the right side of the lower jaw	Plexiform unicystic ameloblastoma	UL	Enucleation, curettage
2011	Kalaskar et al.[23]	9	Male	Right maxilla	Painless swelling	Unicystic ameloblastoma with intraluminal proliferations	UL	Enucleation + Carnoy’s solution and extraction of related teeth
2011	Ponniah[24]	8	Female	Left ramus of the mandible	Painless swelling on the left side of the mandible	Unicystic ameloblastoma	UL	Enucleation then segmental resection
2011	Sudhakara Reddy et al.[25]	6	Female	Anterior mandible	Slow growing painless swelling	Unicystic ameloblastoma	UL	Enucleation and extraction of related teeth followed by application of Carnoy’s solution
2012	Scariot et al.[26]	9	Female	Right mandibular body	Painless swelling	Plexiform unicystic ameloblastoma	UL	Curettage with extraction of two adjacent teeth
2013	Bhutia et al.[27]	5	Male	Right mandible	painless hard swelling	Type 1 unicystic ameloblastoma	UL	Enucleation of the cyst with extraction of the involved teeth followed by application of Carnoy’s solution
2013	Arora et al.[28]	3	Female	Left maxilla	Bony hard swelling	Unicystic ameloblastoma (Type 1.2)	UL	Enucleation of the cyst with extraction of the involved teeth
2014	Present case	10	Female	Right mandible	Swelling with mild pain	Unicystic ameloblastoma	UL	Enucleation with chemical cauterization

Conclusion

Ameloblastomas in children differ from adults with a higher percentage of unicystic tumors. 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. Although enucleation has been claimed to give acceptable recurrence rates in unicystic ameloblastoma, there are no large series with long follow-up in children. The histologic pattern that exhibits mural invasion in unicystic ameloblastoma suggests that more aggressive surgery is necessary. The present case was treated with Carnoy's solution along with the enucleation, which suggests a possible benefit against recurrence.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflict of Interest

There are no conflicts of interest.

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Publication History

Received: 24 June 2018

Accepted: 29 December 2018

Article published online:
28 June 2021