Ameloblastic Fibroma

Ameloblastic fibroma is a rare benign mixed odontogenic tumour with both epithelial and ectomesenchymal components, without formation of dentine or enamel. It makes up about 1 to 2% of odontogenic tumours.

It affects children and young adults, with a mean age under 20 and a majority diagnosed before the age of 20. It usually arises in the posterior mandible and is often linked to an unerupted tooth.

Pathophysiology. The lesion resembles tooth germ, with strands and islands of odontogenic epithelium resembling ameloblasts in a cellular, primitive ectomesenchyme similar to dental papilla.

The epithelium is bland and the mesenchyme is the part that can become malignant, giving ameloblastic fibrosarcoma, either at first or in a recurrence.

Painless swelling of the jaw, with cortical expansion, delayed eruption or displacement of teeth. Many are found on a radiograph of an unerupted tooth. Pain and paraesthesia are unusual.

Rapid growth, pain, cortical destruction, numbness or recurrence after previous surgery suggests malignant change and needs urgent assessment.

• Panoramic radiograph: a unilocular or multilocular, well defined radiolucency, often with a sclerotic border, frequently around the crown of an impacted tooth, and sometimes with root resorption or divergence.
• Cone beam CT or MRI: extent, cortical perforation, relation to the inferior alveolar canal and soft tissue involvement.
• Incisional biopsy before definitive surgery, and examination of the whole specimen. Pathology: epithelial islands and cords in a cellular myxoid mesenchyme, with a hypercellular, atypical or mitotically active stroma raising the concern for sarcoma.
• Chest imaging and staging only when sarcoma is diagnosed.

Differential diagnosis.

• Dentigerous cyst
• Ameloblastic fibro odontoma and odontoma
• Unicystic and conventional ameloblastoma
• Odontogenic myxoma
• Odontogenic keratocyst
• Ameloblastic fibrosarcoma
• Central giant cell granuloma

• Conservative surgery: enucleation with curettage and removal of the associated unerupted tooth when needed, with careful removal of the whole lesion.
• Larger, recurrent or atypical lesions: marginal resection with a 0.5 to 1 cm margin of normal bone, with reconstruction when needed.
• Reported recurrence is about 15 to 20% after enucleation, with a figure of lower certainty from small series. Recurrent lesions carry a higher risk of sarcomatous change.
• Ameloblastic fibrosarcoma: wide resection with clear margins by a head and neck team. Adjuvant therapy is decided by the sarcoma team, and evidence is limited.
• Antibiotics only for infection with spread: amoxicillin 500 mg orally three times daily for 5 days (reduce to 500 mg every 12 hours at eGFR 10 to 30), or clindamycin 300 mg four times daily in penicillin allergy. Use weight based doses in children.

Special groups. Children need paediatric anaesthesia and long term follow up through growth, with attention to preservation of tooth buds and growth centres.

Monitoring. Clinical and radiographic review every 6 months for 2 years, then annually for at least 5 to 10 years.

Referral and escalation. Refer to oral and maxillofacial surgery. Refer to head and neck oncology for recurrence, atypical histology or sarcoma. Urgent referral for rapid growth or destruction.