Ameloblastoma

Dr. Ahmed M. Adawy Professor Emeritus, Dep. Oral & Maxillofacial Surg.

Former Dean, Faculty of Dental MedicineAl-Azhar University

Ameloblastoma is benign, slow-growing but locally invasive neoplasm of odontogenic origin. Theoretically,it may arise from the cell rests of the enamel organ, remnants of dental lamina, epithelial lining of an odontogenic cyst, or basal epithelial cells of the oral mucosa (1). The name “Ameloblastoma” is derived from the old English word ‘‘amel’’ which means enamel, and the Greek word ‘‘blastos’’ meaning germ. It is the second most common odontogenic tumor after Odontomes in prevalence and accounts for approximately 1% of all oral tumors and 18% of all odontogenic tumors

Ameloblastoma

Approximately 80% arise in the mandible, most commonly in the molar-ramus region, occasionally associated with impacted third molars and the remainder occur in the maxilla (2). The peak incidence is in the 3rd-4th decades of life and the male to female ratio is 1:1

Ameloblastoma

Based on clinicoradiographic findings, ameloblastoma is classified into multicystic (solid), unicystic and peripheral subtypes. Multicystic ameloblastoma is the most common type and represent 86% of cases. Peripheral tumors occur solely in the soft tissues covering the tooth-bearing parts of the jaws and have the histological characteristics of intraosseous ameloblastoma (3)

Ameloblastoma

Unicystic ameloblastoma has been identified as a separate entity in 1977 (4). Two histologic variants of unicystic ameloblastoma are described, mural ameloblastomas and luminal ameloblastomas. In mural ameloblastoma, the fibrous wall of the cyst is infiltrated with tumor nodules. In luminal ameloblastoma, the tumor is confined to the luminal surface of the cyst. The tumor often occurs as a painless swelling involving the posterior region of the mandible in younger patients. Radiographically, the tumor presents primarily as a unilocular radiolucency. This variant of ameloblastoma was reported to have less aggressive behavior than the conventional multicystic ameloblastoma

Ameloblastoma

Unicystic ameloblastoma

Histopathologically, ameloblastoma has six types namely; acanthomatous, granular cell, desmoplastic, basal cell, follicular and plexiform whereas, the last two types are more common. Though the treatment options and recurrence rate are irrespective to its histological variants (5)

Ameloblastoma

Most common histological subtypes of ameloblastoma; follicular and plexiform

Two rare forms of malignancy are associated withameloblastoma: malignant ameloblastoma and ameloblastic carcinoma. The cardinal feature of malignant ameloblastoma is metastatic spread. The histologic appearance of the primary and metastatic lesions is indistinguishable from benign ameloblastoma. In contrast, the primary and metastatic lesions of an ameloblastic carcinoma show histologically malignant epithelial features similar to an epidermoid carcinoma (6)

Ameloblastoma

The diagnosis of ameloblastoma is suggested by nonspecific radiographic findings and a thorough physical examination. Nevertheless, a definitive diagnosis is only obtained through a histopathological examinations

Diagnosis

Typically ameloblastoma present as painless slow growing swelling that can progress to great size and cause facial asymmetry, though it may be discovered during routine radiographic examinations. Pain with rapid growth may represent the rare malignant ameloblastoma. Tooth displacement and root resorption are infrequent and usually is an indication of the aggressive nature of the lesion. Paresthesias are uncommon, and can result from perineural invasion

Clinical presentation

Clinical presentation

Maxillary ameloblastoma

Radiographic findings

Radiographically, ameloblastoma shows radiolucent lesion that may have either a unilocular or multilocular appearance. Unicystic ameloblastoma may expand the cortical plate and gives rise to a paper-thin appearance osteolytic lesion usually with scalloped margins, resorption of tooth roots, and impacted molars. The classic ‘‘soap bubble or honeycomb’’ appearance is seen with the most common ameloblastoma, the multilocular type (7). plain X-rays are however, of limited value and lack sensitivity and specificity for the extent of bone and soft tissue invasion

Radiographic findings

Computed tomography

Computed tomography (CT) is the most useful diagnostic imaging modality, typically demonstrating well defined radiolucent uni/multilocular expansible lesions. CT is also useful for the evaluation of cortical destruction and soft tissue extension, identifying the full extent of the tumor to support surgical planning

C T, axial and coronal sections

3-D reconstruction demonstrated a great multicystic ameloblastoma

Differential Diagnosis

However, even when an ameloblastoma shows the typical expansive multilocular appearance, the differential diagnosis can include a variety of odontogenic and nonodontogenic lesions with similar radiographic characteristics namely; aneurysmal bone cyst, odontogenic keratocysistc tumor, ameloblastic fibroma, odontogenic myxoma, giant cell lesions and brown tumor of hyperparathyroidism

Differential Diagnosis

When the lesion presents with a cystic, unilocular and well-defined aspect, the differential diagnosis is typically of odontogenic keratocysistc, dentigerous cyst, residual and radicular cysts or even a traumatic bone cyst. Additionally, peripheral ameloblastomas may resemble lesions such as fistulas, pyogenic granulomas, peripheral giant cell lesions and peripheral odontogenic fibromas (8)

Peripheral ameloblastoma

TreatmentTreatment of ameloblastomas is primarily surgical. There has been some debate regarding the most appropriate method for surgical removal of ameloblastomas. These range from conservative to radical modes of treatment. The conservative modalities include enucleation and curettage; while the radical modalities are marginal, segmental and composite resections. Those advocate conservative approach believe that ameloblastomas though, locally invasive, are essentially benign in nature, therefore, they should be treated as such (9)

Conservative approach in the form of enucleation and curettage is still commonly practiced, despite reported recurrence rates of 55% to 90% for solid multicystic treated conservatively(10). To limit recurrence rates of unicystic ameloblastomas, oral surgeons have extended this procedure to include intra-operative adjuvant treatment of the bony margins with cryotherapy(11), tissue fixatives such as Carnoy’s solution(12), drilling and cautery. The outcomes of the these procedures demonstrate decreased recurrence rates, but still higher recurrences compared with the more extensive radical procedures

Treatment

The ‘‘radical’’ surgical option is the current standard ofcare for ameloblastoma and includes en bloc resection with 1–2 cm bone margins (13) and immediate bone reconstruction. The bony margin is defined as the distance away from the radiographic margin predicted to be disease free and safe to perform osteotomies. It has been documented that ameloblastoma specimens showed microscopic tumor extension 2–8 mm beyond the radiographic boundaries of the tumor (14). Hence, the recommended bone margins are 1–1.5 cm for unicystic and 1.5–2 cm for multicystic histological types. The healthy mucosa overlying cortical perforation is often removed as a margin

Treatment

Segmental resection of the mandible results in discontinuity of the jaw, which is stabilized to its previous position by titanium reconstruction plates to ensure proper occlusion. A fibular free flap is used to restore bone continuity and allow for dental restoration. Reconstructive outcomes show a high rate of success for both esthetic and functional outcomes (15)

Treatment

Following segmental resection, the defect is bridged by free fibular graft and reconstruction plate

Rehabilitation with dental implants

Despite the ‘radical’ nature of a surgical resection, it may actually involve less morbidity than extensive hard and soft tissue resection with associated extensive morbidity that may be warranted in case of recurrence following inadequate primary treatment

Treatment

Follow-up

Follow-up of patients with ameloblastoma should be carried out regularly. As most recurrences present within the first 5 years, yearly follow-up during this period is advisable. Thereafter, follow-up every 2 years seems appropriate but should extend for at least 25 years, as recurrences may appear after a long time (16)

1. Leider AS, Eversole LR, Barkin ME. Cystic ameloblastoma: Aclinico-pathologic analysis. Oral Surg Oral Med Oral Pathol.60:624, 1985.2. Regezi JA, Kerr DA, Courtney RM. Odontogenic tumours: analysis of 706 cases. J Oral Surg. 36:771, 1978.3. Gardner D G, Heikinheimo K, Shear M, et al. Ameloblastomas. In World Health Organization Classification of Tumours. p.296-300. Edited by Barnes L, Eveson JW, Reichart P, Sidransky D. IARC Press, Lyon, France, 2005. 4. Robinson L, Martinez MG. Unicystic ameloblastoma: a prognostically distinct entity. Cancer. 40:2278, 1977. 5. Mendenhall WM, Werning JW, Fernandes R, et al. Ameloblastoma.Am J Clin Oncol 30: 645, 2007.6. Witterick IJ, Parikh S, Mancer K, et al. Malignant ameloblastoma.Am J Otolaryngol. 17: 122, 1996.7. Underhill TE, Katz JO, Pope TL Jr, et al. Radiologic findings of diseases involving the maxilla and mandible. Am J Roentgenol 159:345, 1992.8. Martins, R, Sobrinho J, Rapoport A, et al. Histopathologic features and management of ameloblastoma: study of 20 cases. Rev. Paul. Med. 117:171,1999.

References:

9. Sammartino G, Zarrelli C, Urciuolo V, et al. Effectiveness of a new decisional algorithm in managing mandibular ameloblastomas: A 10-years experience. Br J Oral Maxillofac Surg. 45:306, 2007.10. Hong J, Yun PY, Chung IH, et al. Long term follow up on recurrence of 305 ameloblastoma cases. Int J Oral Maxillofac Surg. 36:283, 2007. 11.Rosenstein T, Pogrel MA, Smith RA, Regezi JA (2001) Cysticameloblastoma—behavior and treatment of 21 cases. J Oral Maxillofac Surg. 59:1311, 2001.12. Lau SL, Samman N. Recurrence related to treatment modalities of unicystic ameloblastoma: a systematic review. Int J Oral Maxillofac Surg. 35:681, 2006.13. Becelli R, Morello R, Renzi G, et al. Treatment of recurrent mandibular ameloblastoma with segmental resection and revascularized fibula free flap. J Craniofac Surg 22:1163, 2011.14. Carlson ER. Ameloblastoma. In: Symposium on odontogenictumors, AAOMS 82nd annual meeting and scientific sessions, San Francisco, CA, September 23, 2000

References:

15. Chana JS, Chang YM, Wei FC, et al. Segmental mandibulectomy and immediate free fibula osteoseptocutaneous flap reconstruction with endosteal implants: an ideal treatment method for mandibular ameloblastoma. Plast Reconstr Surg. 113:80, 2004.16. Demeulemeester LJ, Mommaerts MY, Fossion E, et al. Late loco-regional recurrence after radical resection for mandibular ameloblastomas. Int J Oral Maxillofac Surg. 17:310, 1988.

References: