A Note on Ameloblastoma: pathogenesis, signs & symptoms, Radiographic features & subtypes...etc

Ameloblastoma

Historically, ameloblastoma has been recognized for over a century and a half. Its frequency, persistent local growth, and ability to produce marked deformity before leading to serious debilitation probably account for its early recognition. Recurrence, especially after conservative treatment, has also contributed to the awareness of this lesion.

Pathogenesis 

This neoplasm originates within the mandible or maxilla from epithelium that is involved in the formation of teeth. Potential epithelial sources include the enamel organ, odontogenic rests (rests of Malassez, rests of Serres), reduced enamel epithelium, and the epithelial lining of odontogenic cysts, especially dentigerous cysts. The trigger or stimulus for neoplastic transformation of these epithelial residues is totally unknown.

Mechanisms by which ameloblastomas gain a growth and invasion advantage include overexpression of anti-apoptotic proteins (Bcl-2, Bcl-xL) and interface proteins (fibroblast growth factor [FGF], matrix  metalloproteinases [MMPs]). Ameloblastomas, however, have a low proliferation rate. Mutations of the p53 gene do not appear to play a role in the development or growth of ameloblastoma.

Signs & symptoms

• Occurs predominantly in the fourth and fifth decades of life
• Appears to be no gender predilection (Slightly more in males)
• Mandibular molar-ramus area is the most favored site
• Slowly growing,
• Painless,
• Hard bony swelling or expansion of jaw,
• Thinning of cortical plates produces “Egg shell crackling”.
• Other symptoms – Tooth mobility, root resorption and paresthesia if inferior alveolar nerve is affected.

RADIOLOGICAL FEATURES

• Typically rounded
• Radiographic margins are usually well defined and sclerotic
• Multilocular radiolucency
• Scalloped margins
• When loculations are large, the appearance is called as “SOAP BUBBLE” appearance

• When loculations are smaller, the appearance is called “HONEY COMBED” appearance.

• Buccal & lingual cortical plates are expanded.
• Roots of adjacent teeth displaced / resorbed.
• As it spreads through medullary spaces, radiographic margins are not accurate indication of bone involvement.
• Desmoplastic ameloblastoma, also has a predilection for the anterior jaws and radiographically resembles a fibroosseous lesion (mixed radiopaque-radiolucent)

DIFFERENTIAL DIAGNOSIS

• ODONTOGENIC KERATOCYST
• FIBROUS DYSPLASIA
• OSSIFYING FIBROMA
• CENTRAL GIANT CELL GRANULOMA

BIOLOGIC SUBTYPES

•         Solid/Multicystic Ameloblastoma
•         Unicystic Ameloblastoma

                        Luminal

Tumor is confined to luminal surface of cyst.

Seen as fibrous cyst wall with lining comprised totally / partially of ameloblastic epithelium, showing a basal layer of columnar / cuboidal reversely polarized cells.

Overlying epithelial cells are loosely adhesive, resembling the stellate reticulum of dental organ.

                        Intraluminal

This variant shows the tumor from cyst lining protruding into the lumen of cyst.

Intraluminal projections resemble plexiform ameloblastoma in most cases, though not always. 

                        Mural

In this type, the fibrous wall of the cyst is infiltrated with typical follicular / plexiform ameloblastoma.

      Believed to be more aggressive than other two variants

•         Desmoplastic Ameloblastoma
•         Peripheral Ameloblastoma

•         Malignant Ameloblastoma
•         Ameloblastic carcinoma   

HISTOPATHOLOGICAL SUBTYPES OF SOLID AMELOBLASTOMA

1. FOLLICULAR

Islands of epithelium resemble dental organ surrounded by mature connective stroma.

Individual follicles show central mass of stellate reticulum like cells surrounded by a single peripheral layer of ameloblast like cells.

Nuclei of peripheral cells are reversely polarized.

       Within the islands, cyst formation is common.

2. PLEXIFORM

Instead of islands, long, anastomosing cords and occasional sheets of epithelial cells bounded by columnar / cuboidal cells.

Cells within cords are more loosely arranged than peripheral cells.

Supporting stroma is loose and vascular.

      Cyst formation occurs, not inside follicles, but in surrounding stroma.

3. ACANTHOMATOUS

Central area of follicles show extensive squamous metaplasia, often associated with keratin formation.

DOEAS NOT INDICATE A MORE AGGRESSIVE COURSE OF TUMOR.

Can be confused with squamous cell carcinoma.

4. GRANULAR CELL

Follicles / sheets of cells show granular cell change.

These cells have abundant cytoplasm filled with eosinophilic granules.

Seen in younger persons and appears to be more aggressive clinically.

5. BASAL CELL TYPE

Least common type

Composed of nests / sheets of hyperchromatic basaloid cells

No stellate reticulum present centrally and peripheral cells tend to be cuboidal rather than tall columnar

TREATMENT

• Can vary from simple enucleation to curettage to en bloc resection.
• As lesion spreads through medullary spaces, simple enucleation can leave islands of tumor within the jaws, leading to recurrence.
• Marginal resection is the optimal method.
• Rarely can undergo malignant transformation.