Ameloblastoma is a rare, benign or cancerous tumor of odontogenic epithelium (ameloblasts, or outside portion, of the teeth during development) much more commonly appearing in the lower jaw than the upper jaw. It was recognized in 1827 by Cusack. This type of odontogenic neoplasm was designated as an adamantinoma in 1885 by the French physician Louis-Charles Malassez. It was finally renamed to the modern name ameloblastoma in 1930 by Ivey and Churchill.
While these tumors are rarely malignant or metastatic (that is, they rarely spread to other parts of the body), and progress slowly, the resulting lesions can cause severe abnormalities of the face and jaw leading to severe disfiguration. Additionally, as abnormal cell growth easily infiltrates and destroys surrounding bony tissues, wide surgical excision is required to treat this disorder. If an aggressive tumor is left untreated, it can obstruct the nasal and oral airways making it impossible to breathe without oropharyngeal intervention. The term "ameloblastoma" is .
Types
Four types of ameloblastoma have been described by the WHO 2017 classification:
- Conventional (solid/multicystic) type ameloblastoma
- Unicystic ameloblastoma
- Peripheral/extraosseous ameloblastoma
- Metastasizing ameloblastoma
Conventional ameloblastoma
Previously known as solid/multicystic ameloblastoma. Usually presents with multiple large cystic areas.
Unicystic ameloblastoma
Ameloblastoma with a single cyst cavity account for around 10% of ameloblastomas. Present in younger patients in their second and third decades of life, often in relation to unerupted third molar. The neoplasms are often associated with the presence of unerupted teeth, displacement of adjacent teeth and resorption of roots.
Symptoms include a slow-growing, painless swelling leading to facial deformity. As the swelling gets progressively larger it can impinge on other structures resulting in loose teeth and malocclusion. Bone can also be perforated leading to soft tissue involvement.
Histopathology
thumb|A CT scan of a patient with an ameloblastoma.|alt=<br />thumb|The resected left half of a mandible containing an ameloblastoma, initiated at the third molar
Conventional ameloblastomas have both cystic and solid neoplastic structures.
Solid structure
Solid areas contain fibrous tissue islands or epithelium that interconnect through strands and sheets. The epithelial cells tend to move the nucleus away from the basement membrane to the opposite pole of the cell. This process is called reverse polarization. Two main histological patterns most often occur: follicular and plexiform. Other less common histological variants include acanthomatous, basal cell, and granular cell patterns. A systematic review showed a predilection for males and predominance in fourth and fifth decades in life. 52% of the cases of desmoplastic ameloblastomas showed mandibular involvement, with a tendency to anterior region. The majority of the tumors were found to have ill-defined margins radiographically.
Radiographically, the tumour area appears as a rounded and well-defined lucency in the bone with varying size and features. Numerous cyst-like radiolucent areas can be seen in larger tumours (multi-locular) giving a characteristic "soap bubble" appearance. A single radiolucent area can be seen in smaller tumours (unilocular).
Lingual plate expansion is helpful in diagnosing ameloblastoma as cysts rarely do this. Resorption of roots of involved teeth can be seen in some cases, but is not unique to ameloblastoma. A systematic review found that 79% of desmoplastic ameloblastoma cases were treated by resection. Conservative treatment requires very careful case selection. A systematic review found that 79% of desmoplastic ameloblastoma cases were treated by resection. Chemotherapy is also often ineffective. and some indication that some ameloblastomas might be more responsive to radiation than previously thought. Follow up is important, because 50% of all recurrences occur within 5 years postoperatively. Follicular variants appear to recur more than plexiform variants. Seeding to the bone graft is suspected as a cause of recurrence. Recurrence has been reported to occur as many as 36 years after treatment. To reduce the likelihood of recurrence within grafted bone, meticulous surgery
SMO mutations activate the hedgehog signaling pathway, yielding results similar to V600E, but are less frequently seen. There is also some research suggesting that α<sub>5</sub>β<sub>1</sub> integrin may participate in the local invasiveness of ameloblastomas.
Epidemiology
People with African heritage have been shown to have a higher incidence compared to Caucasians, with the site often being in the midline of the mandible. Ameloblastomas account for about one percent of all oral tumors Men and women are equally affected, though women average four years younger than men when tumors first occur, and tumors run larger in females.