Félix Rojas, Francisco Javier¹; Salazar Navarro, Luis Alonso^1,2; Benítez Pascual, Julio¹; Ríos Burgueño, Efrén Rafael³; Ochoa Viedas, Ricardo³; Urias Barreras, Cynthia Marina^1,3

Language: English/Spanish [Versión en español]
References: 14
Page: 264-271
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ABSTRACT

Introduction: Ameloblastic fibroma is a rare, benign, mixed odontogenic tumor which represents 1.5-6.5% of odontogenic tumors. It is considered a tumor of childhood, with a slight predilection for the male gender. Its most common site of occurrence is the posterior region of the mandible. Its most common treatments, enucleation, and curettage are controversial due to the possibility of recurrence and malignant transformation. Case report: A case of a 12-year-old female patient is reported, with asymptomatic swelling in the left mandible. Radiographically, a multilocular radiolucent area was observed, in the mandibular body and ascending ramus, associated with an impacted and displaced lower second molar. Enucleation and curettage were performed with allograft placement. Microscopic examination revealed a neoplastic proliferation of mesenchymal cells on a myxoid stroma similar to the dental papilla, and of epithelial cells arranged in follicles and cords, with no hard dental tissues. Due to lesion persistence, another surgical intervention was performed with mandibular resection and titanium plates placement. After a thirty months follow-up, the patient does not have lesions and undergoing oral rehabilitation. Conclusion: Ameloblastic fibroma may show an aggressive persistent behavior to a conservative treatment and a radical surgical intervention could be necessary, so long-term follow-up is essential.

INTRODUCTION

The World Health Organization (WHO) defines ameloblastic fibroma (AF) as a rare, benign, true mixed tumor composed of odontogenic mesenchyme resembling dental papilla and epithelial tissue similar to the odontogenic epithelium, without dental hard tissues. It represents 1.5-6.5% of odontogenic tumors and mainly occurs between the first and second decades of life (the mean age is 14.9 years).^1-4

AF has a slight predilection for the male gender, with male-female ratio of 1.4:1. It is seen most frequently in the mandibular posterior region with a mandible to maxilla ratio of 3.3:1. Clinically, it appears with slow-growing, asymptomatic swelling and may cause jaw expansion with facial deformity.^1-6 Radiographically, AF presents as a well-defined, unilocular or multilocular, radiolucent lesion associated with an impacted tooth in most cases, and root resorption and cortical bone perforation may be observed.^1,3

Macroscopically, it is a solid tumor with a smooth external surface and may be encapsulated.¹ Microscopically, the neoplasm shows two components: the mesenchymal component, myxoid and reminiscent of the dental papilla; and the epithelial component, which can be observed in cords of cuboidal to columnar cells, with thickenings that include stellate reticulum-like areas between peripheral epithelial cells similar to dental follicles. In addition, in some cases a fibrous capsule is observed.^1,3,7-9

AF treatment generally involves a conservative surgical approach in small lesions. However, a rate of recurrence is reported in 16% of cases ultra-conservatively treated. When extremely destructive and recurrent lesions, radical surgery is recommended. Malignant transformation to ameloblastic fibrosarcoma (AFS) is rare, but arises from a recurrent AF in 50% of cases.^1,2,4,5,8

An AF case in the posterior mandible is presented, persistent after conservative surgical management, requiring radical surgical treatment.

CASE REPORT

A 12-year-old female patient, referred to an oral and maxillofacial surgery area (Departamento de Cirugía Oral y Maxilofacial del IMSS HGR 1) presenting a facial asymmetry due to swelling in the left lower third, with unknown evolution time (Figure 1A). The patient denied paresthesia, pain and tooth mobility. Her personal and familiar medical history did not contribute to this condition. Intraorally, cortical bone expansion and absence of dental organ (DO) 37 were observed. However, the mucosa was intact and not painful to palpation.

Radiographically, the orthopantomograph (OPG) showed a large, expansive, multilocular radiolucent lesion with sclerotic borders and tiny radiopaque areas, with root resorption of DO 35 and 36, as well as tooth 37 mobility towards the mandibular basal border (Figure 1B). Due to the clinical and radiographic features and the involvement of a DO, the differential diagnosis included a lesion of benign odontogenic origin such as dentigerous cyst, odontogenic keratocyst and AF. Under general anesthesia and orotracheal intubation, enucleation and curettage of the lesion was performed, which showed fibrous characteristics and was detached in portions (Figure 1C). DO 37 was also extracted. Subsequently, an allogeneic graft was placed; the patient reverted without complications and was discharged seven days later.

Macroscopically, the fragmented soft tissue specimen measured 3.0 × 3.0 × 2.0 cm, irregular in shape and surface, light brown color and firm consistency, corresponding to DO 37 (Figure 2A). Microscopically, a benign mixed odontogenic neoplasm was observed. It was featured by the well-defined proliferation of cuboidal to columnar ameloblastic cells, with spindle-shaped nuclei and distal polarization to the basement membrane and moderate to scarce cytoplasm. They were arranged in cords, nests and follicles; their interior showed stellate-reticulum like spindle cells, on a myxoid stroma, with proliferation of mesenchymal cells, exhibiting areas with hyper cellularity, as well as a focus of dystrophic calcifications (Figure 2B-2F). The diagnosis of AF was issued.

Two months after surgery, an OPG for radiographic control showed that there was no evidence of alterations (Figure 3A). At six months follow-up, an OPG revealed a poorly defined radiolucent area, with irregular borders, in the bone graft area (Figure 3B). It was interpreted as persistence of the lesion and the patient was referred to a pediatric hospital (Centro Médico de Pediatría del IMSS, UMAE) in Guadalajara, Jalisco, Mexico, for a radical surgical treatment, which consisted of a mandibular resection with titanium plates placement and a micro vascularized fibular graft (Figure 3C).

Eight months later, slight facial asymmetry is observed extra orally (Figure 4A). On intraoral examination, the mucosa was observed in standard conditions (Figure 4B). After a thirty-month follow-up, the patient is free of lesions and is in an oral rehabilitation process through implants placement, with the aim of recovering masticatory function and aesthetics (Figure 3D).

DISCUSSION

AF is a relatively uncommon benign mixed odontogenic tumor that occurs primarily in the first to second decades of life, with a mean age of 14 years and most cases occur before 22.¹ However, cases of 7-week-old patients³ and also 38-year-old patients have been reported in literature.⁴ This tumor has a slight predilection for the male gender.¹ In an analysis of 172 AF cases, differences in gender distribution were not statistically significant.⁵ Its most common location is the mandible in the posterior region and most of the maxillary lesions occur in the anterior region.⁵ However, Côrte et al.⁶ reported an AF case in the mastoid segment of the temporal bone.

Clinically, this lesion in general presents swelling and cortical expansion with facial deformity. Radiographically, AF shows unilocular or multilocular well-defined radiolucencies, associated with an impacted tooth up to 80% of cases.¹ Due to this, some authors mention that this lesion is often confused with ameloblastoma and dentigerous cyst.⁷ Usually unilocular lesions are small and asymptomatic, while multilocular ones are associated with larger and more destructive lesions.^1,7 These clinical and radiographic features being consistent with our findings.

When an inductive modification produced a deposition of dentin or dentin plus enamel, this histopathological feature was called ameloblastic fibrodentinoma (AFD) and ameloblastic fibroodontoma (AFO) respectively.^1,7 The current WHO classification emphasizes that such hard tissue formation is usually the first stage of maturation and is more consistent with a developing odontoma.^1,8,9 This position remains controversial as it is recognized that some of these lesions (AFD, AFO) may reach large sizes and arise in age groups which are not always consistent with a hamartomatous lesion such as odontomas,⁹ as observed by Chrcanovic et al.¹⁰ they found some cases of AFD and AFO affected patients older than 20 years, which exceeds the expected age for dental formation. Furthermore, the mean age of patients with these lesions was very similar, which does not support the concept of progressive maturation of these tumoral conditions, and suggests that some AFDs and AFOs are truly neoplastic lesions.

Recently, some molecular features of these mixed odontogenic tumors have been reported, pointing out that AF, AFD and AFO show BRAF gene mutations in the mesenchymal component, unlike odontoma which does not show such alteration, suggesting that at least a subset of AF, AFD, and AFO are molecularly distinct from odontoma, and may represent distinct entities and be neoplastic.¹¹

AF management could be a challenge. Currently there is no consensus regarding to the best surgical approach. Treatment may vary from a conservative method as enucleation and curettage, to radical treatments such as marginal or segmental resection. Small and asymptomatic tumors (especially in little children) are conservatively removed and for extensive and destructive tumors a radical surgery is recommended.^1,2

De Campos et al.⁸ report the case of a pediatric patient diagnosed with locally aggressive AF who underwent conservative surgery, with a 12 years follow-up and no signs of recurrence of the lesion, which suggests that a conservative treatment in young patients is effective and offers a reducing surgical morbidity. Regarding this, Mosby et al.³ and Buchner et al.⁵ suggest that conservative treatment may sometimes cause recurrence, which actually is the proliferation of a residual tumor. On the other hand, Sanadi et al.² report the case of an adult patient who underwent radical surgery at the beginning, considering the possibility of recurrence and malignant transformation of this lesion. Buchner et al.⁵ state that the recurrence rates could be biased as the studies reporting relatively high rates of recurrence and malignant transformations are mainly based on case reports available in the literature, thus cannot be calculated accurately. However, it has been questioned whether AF treatment protocols should be reviewed, since 44% of AFS arise from recurrent AF.^12,13 Recently, AFS molecular features have been identified, highlighting frequent BRAF and occasional NRAS mutations and it has been suggested that AFS should be tested for these mutations, given the availability of approved promising drugs targeting the mutant BRAF gene.¹⁴

In our case a conservative approach was used as the first surgical intervention, considering patient's age and later a radical surgical approach due to the lesion persistence. There must be an individualized surgical treatment in each and every case, with a careful inspection, considering the patient's age, lesion size, histopathological findings, possibility of recurrence and malignant transformation.

CONCLUSION

AF may show an aggressive persistent behavior to a conservative treatment and a radical surgical intervention could be necessary, so long-term follow-up is essential.

REFERENCES

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10. Chrcanovic BR, Gomez RS. Ameloblastic fibrodentinoma and ameloblastic fibro-odontoma: an updated systematic review of cases reported in the literature. J Oral Maxillofac Surg. 2017; 75 (7): 1425-1437.

11. Coura BP, Bernardes VF, de Sousa SF, Diniz MG, Moreira RG, de Andrade BAB et al. Targeted next-generation sequencing and allele-specific quantitative PCR of laser capture microdissected samples uncover molecular differences in mixed odontogenic tumors. J Mol Diagn. 2020; 22 (12): 1393-1399.

12. Munisekhar MS, Shylaja S, Kumar RV, Rao KA, Patil SR, Alam MK. Ameloblastic fibrosarcoma - a rarity? JPRAS Open. 2019; 21: 56-62.

13. Onda T, Yamazaki A, Hayashi K, Iwasaki T, Hashimoto K, Takano M. Ameloblastic fibroma in mandibular anterior tooth region: a case report. Bull Tokyo Dent Coll. 2021; 62 (1): 49-54.

14. Agaimy A, Skalova A, Franchi A, Alshagroud R, Gill AJ, Stoeher R et al. Ameloblastic fibrosarcoma: clinicopathological and molecular analysis of seven cases highlighting frequent BRAF and occasional NRAS mutations. Histopathology. 2020; 76 (6): 814-821.

AFFILIATIONS

¹ Facultad de Odontología, Universidad Autónoma de Sinaloa. México.

² Servicio de Cirugía Oral y Maxilofacial, Hospital General Regional No. 1, IMSS. México.

³ Servicio de Anatomía Patológica, Centro de Investigación y Docencia en Ciencias de la Salud, Universidad Autónoma de Sinaloa. México.

CORRESPONDENCE

Cynthia Marina Urias Barreras. E-mail: cynthia.urias@uas.edu.mx

Received: Mayo 2021. Accepted: Agosto 2021.