Clinical features of giant hybrid ameloblastoma of the mandible: A case report with long-term observation of natural growth before treatment

Abstract

Hybrid ameloblastoma comprising desmoplastic and solid type ameloblastoma with classic follicular or plexiform pattern is a known unusual variant. Ameloblastoma, including the hybrid type, is a slow growing tumor, and there is very little information regarding growth of such tumors when left untreated. We present here the clinical features of a giant hybrid ameloblastoma of the mandible together with extended radiographic observation before the patient consented to surgery. A 62-year-old Japanese man was referred in 2002 with a chief complaint of a left-sided mandibular swelling. Panoramic X-ray showed a multilocular radiolucent lesion extending from the left mandibular angle to the ascending ramus, including an impacted wisdom tooth with root resorption. Biopsy specimen examination revealed myxofibrous tissue with some odontogenic epithelial nests. The clinical diagnosis was odontogenic myxoma or myxofibroma of the left side of the mandible. At that time, the patient declined surgical treatment. The tumor gradually increased in size over 7 years of follow-up, and he finally consented to undergo surgical treatment when the tumor began approaching the skull base. Tumorectomy including hemimandibulectomy and plate reconstruction of the mandible were performed in 2009. Histopathology revealed follicular and desmoplastic ameloblastoma with myxomatous change and was diagnosed as hybrid ameloblastoma. No recurrence was seen at the 24-month follow-up examination, and mandibular reconstruction using bone regeneration and oral rehabilitation with a dental implant were performed. Further clinicopathological analysis of coexisting desmoplastic ameloblastoma and non-desmoplastic ameloblastoma is needed to understand the significance and biological behavior of this hybrid variant.

Highlights

  • Hybrid ameloblastoma comprising desmoplastic and solid type ameloblastoma with classic follicular or plexiform pattern is a known unusual variant.

  • We present the clinical features of a giant hybrid ameloblastoma of the mandible together with extended radiographic observation before the patient consented to surgery.

  • The tumor was displayed follicular, plexiform, acanthomatous and desmoplastic components, similar to those described in previous reports.

  • In the present case, the 11 years observation from the time of the tumor development without symptom was possible and the growth rate is relatively low compared with the previous cases, in which the analysis used symptom duration to represent disease duration in the growth rate formula.

Introduction

Ameloblastoma is a benign odontogenic tumor, accounting for 1% of all cysts and tumors of the jaw and 11% of all odontogenic tumors. It has a tendency for aggressive invasion of the jaw, a high rate of recurrence, and rare malignant transformation with lymph node metastasis [ ]. Ameloblastoma is localized to the maxilla in 20% of cases and to the mandible in the remaining 80%. Over 57% of ameloblastomas in the mandible are located in the molar region or ascending ramus [ ]. According to the 2005 World Health Organization classification of odontogenic tumors, ameloblastoma can be further classified as solid/multicystic, extraosseous/peripheral, desmoplastic, and unicystic types. Several histopathological patterns of ameloblastoma have been reported, including follicular, plexiform, acanthomatous, keratinizing, granular cell, basal cell, desmoplastic, and spindle cell. The treatment depends on the subtypes of ameloblastoma. Solid/multicystic and desmoplastic types are treated by excision with an adequate margin of uninvolved tissues and extraosseous/peripheral type is treated by conservative excision. In unicystic type, enucleation could be carried out for luminal variant and further surgical intervention in mural variant must be considered depending on the depth of epithelium invasion into the cyst wall [ ]. In 1987, Waldron and El-Mofty first reported an unusual variant described as a “hybrid” lesion, consisting of both desmoplastic ameloblastoma and solid ameloblastoma with a classic follicular or plexiform pattern [ ].

Ameloblastoma is considered a slow-growing tumor and is generally treated with either conservative management or radical surgery at the time of first presentation. Therefore, few studies offer any information about the growth of these tumors if left untreated [ ]. This clinical case report presents a rare case of a giant hybrid ameloblastoma of the mandible that was observed radiographically during an extended period of growth before the patient finally consented to surgery.

Case report

A 62-year-old Japanese man was referred to the Department of Oral and Maxillofacial Surgery of Shimane University Hospital in June 2002 with a chief complaint of swelling on the left side of the mandible. He had a past medical history of hepatitis type C and idiopathic thrombocytopenic purpura and was being followed up with treatment for both conditions. On initial examination, the lower aspect of the face appeared symmetrical, but a bony swelling was found intraorally extending from the left retromolar region to the ascending ramus ( Fig. 1 A). There was no pain or paresthesia in the left mental region. Panoramic X-ray showed a multilocular radiolucent lesion, including an impacted left lower wisdom tooth accompanied by root resorption, in the ascending ramus region. The radiolucent area is apparent under the lower left wisdom tooth in the panoramic X-ray in 1996, which was provided by the patient’s dental practitioner ( Fig. 1 B–D). The clinical diagnosis was odontogenic tumor, possibly keratocystic odontogenic tumor, ameloblastoma, or myxoma, of the left side of the mandible. Examination of a biopsy specimen taken from the intraosseous lesion revealed myxofibrous tissue with some odontogenic epithelium ( Fig. 1 E), and the pathological diagnosis was odontogenic myxoma or myxofibroma. We explained the clinical diagnosis and the need for tumorectomy and segmental mandibulectomy to the patient but he declined surgical treatment therefore, only follow-up examinations were undertaken. The tumor gradually expanded, with further asymmetry of the lower face due to increased swelling ( Fig. 2 ). The patient continued to refuse surgical treatment during the next 7 years of follow-up but finally consented when the tumor began to approach the skull base ( Fig. 2 C). Tumorectomy including hemimandibulectomy and reconstruction of the mandible using a titanium plate were performed in December 2009 under general anesthesia ( Fig. 3 ). The excised specimen was 135 × 90 × 80 mm and weighed 437 g.

Fig. 1
(A) Intraoral photograph shows swelling from the left retromolar to ascending ramus region. (B) Panoramic X-ray shows a multilocular radiolucent lesion including an impacted wisdom tooth with root resorption. (C) Axial computed tomography shows an expanded low-density area in the left-side mandible with cortical bone resorption including an impacted wisdom tooth. (D) Panoramic X-ray in 1996 shows a radiolucent area is apparent under the lower left wisdom tooth (image courtesy of the patient’s dental practitioner). (E) Histopathological features of the biopsy specimen (hematoxylin and eosin stain; original magnification, ×10) include myxofibrous tissue with odontogenic epithelium.
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Aug 8, 2020 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Clinical features of giant hybrid ameloblastoma of the mandible: A case report with long-term observation of natural growth before treatment
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