Recurrence of ameloblastoma in an autogenous bone graft 10 years after initial operation: A case report and literature review

Background: Ameloblastoma is an asymptomatic locally invasive slow-growing odontogenic epithelial tumor. it is rare that the tumor developing in the autogenous bone graft. Case presentation: This report describes a case of ameloblastoma recurrence in an autogenous iliac bone graft 10 years after initial operation in a 37-year-old female who had a history of partial mandibulectomy + left iliac bone graft for ameloblastoma. In 2016 year, the patient was therefore admitted to our hospital for a second surgery, In 2017, 2018, 2019 after the second surgery, radiograph examination showed no recurrence after the surgery. Conclusions: Awareness of the concept of tumor-free operation, extensively resect the affected bone and soft tissue may help in ameloblastoma recurrence, Pathological diagnosis and long-term regular follow-up visits should help improve long-term outcome


Background
Ameloblastoma is an asymptomatic locally invasive slow-growing odontogenic epithelial tumor. the classi cation of ameloblastomas has been simpli ed and narrowed to ameloblastoma, unicystic ameloblastoma and extraosseous/peripheral types [1]. So many reports on local recurrence of ameloblastoma, however, Recurrence of ameloblastoma in autogenous iliac bone grafts has rarely been reported in the literature. Here, we discuss a case of recurrent ameloblastoma in an autogenous iliac bone graft 10 years after initial operation (partial mandibulectomy + left iliac bone grafts) and review the literature on recurrent ameloblastomas in the bone graft.

Case Presentation
In 2016, a 37-year-old female reported discomfort during mastication and dull pain in the left mandibular bone over the course of a month. At hospital examination, according to our records, we found she had been admitted to our surgical center in 2006 and safely received partial mandibulectomy surgery through an intraoral approach, whereby the mandible defect was reconstructed with the left autogenous iliac bone. The mandible was diagnosed with ameloblastoma upon pathological examination, but the histological subtype of the ameloblastoma was not reported.
In 2016, however, the patient returned to the hospital. Clinical examination revealed facial swelling and tenderness of the left mandible and increased mandibular volume in the left region of the mandible with no remarkable in ammation. Panoramic radiographs showed a large multilocular radiolucency occupying in the left mandibular grafted bone and metal wires (Fig. 1). Three-dimensional computed tomography (CT) of the maxillofacial region showed expansion of the grafted bone with multilocular radiolucency of 33 mm × 24 mm, but no extension of the tumor mass to adjacent soft tissue (Fig. 2).
The patient was therefore admitted to the hospital for a second surgery. The expanded grafted bone was resected completely, the excision of the lesion with 1 cm uninvolved mandible margin was performed,and the mandible was reconstructed using her right iliac bone, which was xed and installed using titanium plates. Histopathological features revealed follicular ameloblastoma with acanthomatous changes with tumor-free margins (Fig. 3). A photomicrograph of the original tumor showed formation of keratinized beads (Fig. 4) and that the nuclei were arranged in a fence shape and were far from the basement membrane, that is, polarity was inverted.

Discussion
Various prognoses of postoperative ameloblastoma have been reported based on type of surgery, including enucleation, curettage, and radical resection [2].
Almeida et al. [3] found that the recurrence rate after conservative treatment was 3.15 times higher than that after radical resection. According to Carlson et al. [4], conservative measures such as enucleation, enucleation and curettage, surgical excision and peripheral ostectomy, and enucleation with liquid nitrogen cryotherapy, it means an inadequate removal of tumor, but radical resection means the soft and hard tissue margins in the resection of tumor are determined to be histopathologically negative.
Regarding some patients are younger, there is a tendency towards more conservative measures for the aesthetic, functional, and psychological effects [3]. Radical resection is indicated for the solid or multicystic ameloblastoma [4,5], these principles of radical resection will increase the likelihood of tumorfree margins in the nal histopathologic sections: assessment of anatomic barriers; resection with 1 cm to 1.5 cm linear bone margins; the use of specimen radiographs and the use of frozen section.
Additionally, the initial surgical approach was correlated with the recurrence risk [6]. In our report, intraoperative frozen pathological examination was not performed during the rst operation in 2006. So that the patient with simultaneous radical resection and bone reconstruction, should be performed the radical surgery to ensure that the stump of the bone is normal, and there was no tumor cell surrounding the soft tissue.Regardless of treatment method, regular follow-up is necessary after surgery. Almeida et al. [3] suggested that panoramic lms should be reviewed every six months for the rst ve years after surgery, every year for 5-10 years after surgery, and every 2-3 years after 10 years. In our report, the follow-up of the patient was irregular and unsustainable because of the relatively low levels of dental care in China. Now the electronic medical record information in our city is gradually developing, Patients are not regularly followed-up can be reached and remaindered .
Patients with concurrent radical resection and bone reconstruction should receive regular follow-up for at least 10 years, it was the signi cant factor that could be helpful in early diagnosis and therapy. If recurrent ameloblastoma is suspected during re-examination, CT may be required.
At present, the mechanism of recurrent ameloblastoma in grafted bone is still unclear [25]. Three possible explanations of the recurrence of ameloblastoma in grafted bone have been reported: i.e., 1) residual tumor cells in stumps; 2) residual tumor cells in soft tissues; and 3) tumor cells implanted in the bone during operation [14,18]. According to our case, the patient's three-dimensional CT showed that the recurrent lesions in the mandible bone were mainly invasive, i.e., the lesions invaded the grafted autogenous bone, resulting in a polycystic change. According to the clinical manifestations and auxiliary examination of the patient, A 1 cm to 1.5 cm bony linear margin and an intraoperative specimen radiograph could provide a margin-free specimen [4]. This standard of the surgery is an opportunity to assess the adequacy of the resection. Encounter the anatomic barrier of cortical bone, this should be assessed and determined preoperatively and precisely dissected intraoperatively, it depends on the experience of the surgeon. In our case, en-bloc resection and affected surrounding soft tissue maybe a cause of the second recurrence. This is consistent with the literature [6,8,12,14,15,18,19]. We still need to follow up patients continuously, and we look forward to more studies.

Conclusions
Here, we reported on a case of recurrent ameloblastoma after 10 years. We should pay attention to the concept of tumor-free operation, extensively resect the affected bone and soft tissue, carefully treat the stump, and then transplant the autogenous iliac bone to restore the defective mandibular shape and function. At the same time, Pathological diagnosis and long-term and regular follow-up visits should help improve long-term outcome.   Availability of data and materials All data generated or analyzed are included in this published article.
Ethics approval and consent to participate Panoramic radiographs showed a large multilocular radiolucency occupying the left mandibular graft bone and metal wires.