Conservative treatment of unicystic mural ameloblastoma

Abstract

Mural ameloblastoma is a subtype of Unicystic Ameloblastoma characterised by the expansion or infiltration of tumour nodules into the fibrous wall of the cyst. The behaviour of this subtype is highly aggressive, with a risk of recurrence comparable with that of Conventional Ameloblastoma. Consequently, the preferred treatment for Unicystic mural Ameloblastom is broad resection of the tumour. In this case report we describe the successful conservative treatment of a Unicystic mural Ameloblastom associated with an impacted tooth. The conservative treatment consinsted in a initial marsupialization followed by the enucleation of the lesion performed with a lateral corticotomy to create a “bone door” and the relocation of the “bone door” using microplates and titanium screws.

Our conservative approach preserved the integrity of the inferior alveolar nerve as well as mandibular functionality and resulted in a good aesthetic outcome.

Due to the behaviour of this lesion, a strict follow up is mandatory. In our experience, follow-up is conducted as long as possible regardless of the surgical treatment. This protocol includes Cone Beam CT performed 1 year after surgery and panoramic radiology (OPG) once a year until 5 years after surgery. OPG is then repeated every 3 years in patients with Unicystic Ameloblastoma and every 2 years in those with Conventional Ameloblastoma or ameloblastoma with mural invasion. Suspected recurrence should be evaluated by CBCT.

Highlights

  • Unicystic Mural Ameloblastoma has a high risk of recurrence, so the resection is the indicated treatment.

  • Conservative treatment allows to preserve the mandibular function and the integrity of the inferior alveolar nerve.

  • Conservative treatment demands patient compliance and strict radiographic recalls.

  • The post operative follow up is mandatory in order to intercept early recurrences.

Introduction

Ameloblastoma is a benign tumour of epithelial origin. It is locally aggressive, increases to large volumes and has a high risk of recurrence. The most common variants are conventional ameloblastoma (CA) and unicystic ameloblastoma (UA). CA is the most aggressive form and has a tendency of recurring multiple times, whereas UA is a peculiar subtype distinguished by a more benign, less aggressive behaviour [ ].

In 1988, Ackermann [ ] divided UAs into three growth patterns: luminal, intraluminal and mural. In the intraluminal subtype, the ameloblastic node protrudes from the cystic border into the lumen. In the luminal variant, the tumour node are contained within the ameloblastic cystic surface, and mural ameloblastomas are characterised by the expansion or infiltration of tumour nodules into the fibrous wall of the cyst.

The intraluminal and luminal variants are considered to be less aggressive and to have a lower risk of recurrence, whereas the mural subtype is highly aggressive, with a risk of recurrence comparable with that of CA. The behaviour of the mural subtype is supported by the study by Li et al. [ ], in which high levels of proliferating cell nuclear antigen and Ki-67 antigen were found in mural ameloblastomas. These findings are consistent with the ability of tumour islands in the fibrous wall to invade the surrounding cancellous bone. Consequently, the preferred treatment for mural UA is broad resection of the tumour [ , ].

However, in this case report we describe the successful conservative treatment of a mural UA associated with an impacted tooth. Our conservative approach preserved the integrity of the inferior alveolar nerve (IAN) as well as mandibular functionality and resulted in a good aesthetic outcome.

Case presentation

A 31-year-old male arrived at our clinic complaining of facial deformity, intraoral mandibular swelling and biting-related ulcers since the previous month. The patient reported neither pathologies nor allergies.

Panoramic radiography (OPG) revealed absence of the medial portion of the mandibular ramus with interruption of the mandibular canal and impaction of tooth 4.8. Cone beam CT (CBCT) showed the amplitude of the lesion and cortical bone loss on both the lingual and buccal sides, as well as thinning of the bone base. In addition, the canal of the IAN was compromised ( Fig. 1 A).

Fig. 1
Radiographic images of the Unicystic Ameloblastoma (UA): A) CBCT scans at the diagnostic phase: cortical bone loss on both the lingual and buccal side is evident, as well as thinning of the basal bone. In addition, the IAN canal was involved and compromised. B) CBCT scans 6 months after marsupialization (first surgical step): evidence of new bone formation, reappearance of cortical borders, both on the lingual and the vestibular side; volume cyst reduction and channelling of IAN canal. C) Radiographic control (CBCT) 12 months after enucleation (second surgical step) revealed almost complete remineralisation of the osteolytic area, with partial disappearance of the ostetomised and repositioned bone segment. D) CBCT scans taken 36 months from the surgical reintervention (third surgical approach): Evidence of complete repair of the bone defect, with rearrangement of the medullary bone, remineralisation of the cortical bone with complete canalisation of the mandibular canal and absence of recurrences. CBCT= Cone Beam Computed Tomography, IAN = Inferior Alveolar Nerve, UA = Unicystic Ameloblastoma.

The preliminary diagnosis was odontogenic cyst or ameloblastoma.A small portion of the cystic wall was harvested for histological examination (sample size 0.8×0.6 × 0.5 cm). The cystic membrane was marsupialised and a gauze was placed in the cavity to maintain patency ( Fig. 2 ).

Fig. 2
Clinical images of the first surgical approach performed in order to biopsy the lesion. A) Removal of a portion of the cystic wall, harvested for histological examination. B) The cystic cavity, was periodically irrigated with hydrogen peroxide (10 vol)/chlorhexidine (0.2%). C) The cavity was filled with gentamicin-soaked gauze to maintain patency.

During the first postoperative month, the surgical site was rinsed weekly and then the patient was followed-up monthly at the clinic.

The histological report was compatible with a diagnosis of mural UA with a follicular pattern ( Fig. 3 A). Given the patient’s age and functional and aesthetic considerations, the marsupialization was maintained until the cortical rim of the mandibular canal had remineralised.

Fig. 3
Histological images of the collected samples. A) Sample at first surgical step: Hematoxylin and Eosin (H&E), 4x. Odontogenic epithelium arranged in follicular pattern. Variably sized clusters of cells composed of central loosely arranged areas with basal cell components, surrounded by columnar epithelial cells with clear and vacuolated cytoplasm and hyperchromatic nuclei. Nuclei were aligned at the periphery away from the basement membrane. Absence of significant nuclear pleomorphism and inconspicuous mitotic activity. Microcyst changes were appreciable as well as minimal stroma with moderate fibrous tissue component. B) Sample at the second surgical step. Hematoxylin and Eosin (H&E), 4x. Odontogenic epithelium arranged in follicular pattern. Sheets and nests of basoloid cells with peripheral palisading were evident. The cells showed hyperchromatic nuclei and reduced mitotic activity. The remaining mucosa presented ulcerated areas with chronic inflammation. C) Sample at the third surgical step. Hematoxylin and Eosin (H&E), 4x. Odontogenic epithelium is arranged in follicular pattern. Isolated foci of basaloid cells with peripheral palisading. Stroma presented marked reactive fibrous tissue components.
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Mar 21, 2021 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Conservative treatment of unicystic mural ameloblastoma
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