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Classification of Ameloblastoma:

Based on clinical, radiographic & histopathology & behavioural & prognostic aspects, Ameloblastoma is classified as:

  1. Classic- Solid/ Multicystic ameloblastoma (SMA)
  2. Unicystic ameloblastoma (UA)
  3. Peripheral ameloblastoma (PA)
  4. Desmoplastic ameloblastoma (DA), including hybrid lesion.

 Solid/ Multicystic Ameloblastoma (SMA)

Clinical Features:

  • Benign epithelial tumour, with almost no tendency to metastasize. Though it is locally invasive.
  • High recurrence if improperly removed
  • Located centrally (intraosseous).
  • Few or no clinical signs in early stages.
  • Later signs:
  • Facial deformity, loose teeth
  • Spontaneous fracture may be seen.
  • Bony swelling may be seen
  • Pain: Due to either pressure of growing tumour on nerves or secondary infection.
  • Enlarging tumour makes the surrounding bone elicit Crepitation/ Egg shell crackling
  • Perforation of bone may occur.

Radiographic features:

  • Multilocular lesion- typical appearance
  • Unilocular may also be seen.
  • Unilocular:
  • Well defined single radiolucency.
  • If associated with unerupted tooth, may resemble Dentigerous cyst or OKC.


  • Black> White
  • Age– 35-37 yrs average age at time of diagnosis.
  • According to Gardener, mean age at time of diagnosis:
  • SMA– about 39 yrs
  • Unicystic– about 22 yrs
  • Peripheral– about 51 yrs
  • Gender– almost equal or slight male (1.1:1) predilection.
  • Location: Mandible> Maxilla (2.2:1)
  • Posterior mandible> anterior mandible> posterior maxilla> anterior maxilla



  • Mostly arise from odontogenic epithelial remnants, specifically remnants of dental lamina.
  • If these remnants lie outside bone in soft tissues, they form Peripheral Ameloblastoma.
  • May arise as neoplastic change in lining or wall of cysts like Dentigerous or OKC called Mural ameloblastoma. (usually seen in posterior region).
  • May originate from Epithelial rests of Malassez.


WHO 1992 definition: A polymorphic neoplasm consisting of proliferating odontogenic epithelium which usually has a follicular or plexiform pattern lying in a fibrous stroma.

The various histologic patterns of SMA include:

Follicular pattern

  • Epithelial Islands: Contain central mass of polyhedral cells, or loosely connected angular cells resembling stellate reticulum.
  • Peripheral cells in the epithelial islands are cuboidal or columnar resembling inner enamel epithelium or pre-ameloblast.
  • Cystic degeneration is common within epithelial islands

Plexiform pattern

  • Tumour epithelium arranged as a network
  • This network bound by cuboidal to columnar cells & includes Stellate Reticulum like cells.
  • Cyst formation is due to stromal degeneration may be seen.
  • Hyaline bodies like odontogenic cyst epithelium/wall may be seen

Acanthomatous SMA:

  • Extensive squamous metaplasia
  • Keratin may be formed sometimes (within tumour island)
  • Generally, shows follicular pattern
  • Third most common histologic type.

Granular cell SMA:

  • Most often it shows Follicular pattern.
  • Granular transformation of central stellate cells.
  • Granular cells may be Cuboidal, Columnar or Round.
  • Cytoplasm filled with Acidophilic granules.
  • Granularity may be due to increased apoptosis & phagocytosis of cells by neighbouring neoplastic cells.

Desmoplastic SMA:

  • Usually follicular pattern of SMA
  • Connective tissue shows marked hyalinization (desmoplasia).

Basal cell SMA:

  • Resemble basal & suprabasal spinosum cells.
  • Rare variant
  • SMA shows predominant basaloid pattern.
  • Most actively proliferating type. It shows positive labelling for bothPCNA & KP-67. 
  • This variant has most immature cells.

Clear cell SMA:

  • Clear cells in stellate cell area of SMA follicles
  • PAS positive
  • May show malignant transformation.

Keratoameloblastoma(KA) & papilliferous KA:

  • Simultaneous occurrence of areas of Ameloblastoma with pronounced keratinization & cystic areas of resembling OKC.
  • Extremely rare.

Connective tissue of all histologic variants of SMA:

  • Contains fibroblasts, collagen fibres & myofibroblasts.


  • Treatment ranges from simple enucleation and curettage to en bloc resection.
  • Curettage only, often leave small islands of tumor within the bone, this results in recurrences (50-90%).
  • Marginal resection: Most widely used treatment, but recurrence of up to 15% may be seen.
  • Removal of the tumor, followed by peripheral ostectomy, often reduces the need for extensive reconstructive surgery.
  • Ameloblastomas of the posterior maxilla are particularly dangerous because of the difficulty of obtaining an adequate surgical margin around the tumor.
  • Though ameloblastoma is radiosensitive, Radiation therapy is contraindicated because of a possibility of secondary radiation-induced malignancy.

Unicystic Ameloblastoma

  • Well defined, often large monocystic cavity with a lining.
  • Locally but rarely entirely lined by odontogenic epithelium.
  • On the Luminal surface of cyst, one or several polypoid or papillomatous, pedunculated exophytic masses may be seen: These are called Intracystic, Luminal or Intraluminal ameloblastoma.
  • Epithelial nodules may grow within the connective tissue: Called Mural or Intramural.
  • May be associated with an unerupted tooth.

Clinical & Radiographic findings:

  • If there is secondary infection:
  • Local swelling
  • Occasional pain
  • Lip numbness
  • Discharge or drainage
  • May be unilocular or multilocular; Unilocular more common
  • Root resorption is common.
  • If crown of unerupted tooth is involved, it is displaced by cystic tumour rather than project into cystic lumen – Differentiation from Dentigerous cyst.


  • Tooth associated lesion occurs in younger patients compared to those not associated with tooth. 
  • Males: Tooth associated lesion more common; Females: Lesion without tooth are common.
  • Mandible > Maxilla; Posterior mandible & ascending ramus is most commonly involved.



  • May arise from pre-existing odontogenic cyst (commonly Dentigerous cyst) or it may arise de novo.
  • According to Leider et al.: They may arise from:
  1. From REE.
  2. From Dentigerous or another odontogenic cyst.
  3. From Solid ameloblastoma undergoing cystic degeneration.


  • Minimum criteria for diagnosing a lesion a unicystic ameloblastoma:
  • Single cystic sac.
  • Lined by odontogenic epithelium (usually present locally).
  • Epithelium may be variable, mimicking lining of Dentigerous or Radicular cyst.

Sub-groups of unicystic ameloblastoma:

Luminal type:

  • Epithelial lining may show transformation to cuboidal or columnar basal cells.
  • Nuclear palisading with polarization.
  • Cytoplasmic vacuolization.
  • Intercellular spacing.
  • Sub-epithelial hyalinization.

Intramural tissue:

  • Infiltration from cyst lining or as free islands of follicles (SMA) often with central cystic degeneration.
  • About 2/3 of both tooth-associated & non-tooth-associated show intramural invasion.
  • Though slightly more common in non-tooth type.
  • Intra luminal proliferation more common in tooth associated type.
  • Tumours with intramural invasion have higher recurrence.


  • May be treated conservatively by enucleation or it may need aggressive treatment as classic SMA, depending on the histopathologic presentation.

Peripheral Ameloblastoma:

  • Peripheral ameloblastoma is a benign neoplasm or hamartomatous lesion confined to soft tissue overlying tooth bearing area of jaws.
  • Several characteristic similar to SMA.
  • Do not invade underlying bone.

Clinical & Radiographic features:

  • Painless, sessile, firm & exophytic growth.
  • Surface is relatively smooth, but may be granular or pebbly. Sometimes Papillary or Warty.
  • Surface colour:  Normal to red to dark red.
  • Size– 0.3 to 4.5 cm (1.3 cm)
  • Superficial bone erosion may be seen, due to pressure of lesion.


  • 2-10% of all Ameloblastomas.
  • Age9-92 yrs. (Average age: 52 yrs.). More common in 5th to 7th decade.
  • Gender: more common in males.
  • Location: more common in mandible. Mandibular premolar region most common site.



  • Probably arises from dental lamina remnants. (cell rests of Serre).
  • May also arise from surface epithelium. Continuity between tumour & surface epithelium has been seen.



  • Epithelial islands show palisaded columnar basal cells.
  • Stellate reticulum like cells are few in number (negligible).
  • Lesions exhibiting Acanthomatous areas are difficult to distinguise from Basal cell carcinoma.
  • Ghost cells in Acanthomatous area may be seen. May be confused with Calcifying ghost cell odontogenic cyst.
  • Vacuolated or clear cells may be seen in some parts of tumour as clusters.


  • Mature fibrous connective tissue (calcification may be seen sometimes).


  • It exhibits a milder biologic behaviour than the SMA. So, wide excision is usually not needed.
  • Conservative supra-periosteal surgical excision with adequate disease-free margins.
  • Recurrence rate lower than SMA.

Desmoplastic Ameloblastoma

  • Extensive stromal collagenisation or desmoplasia.
  • Hybrid ameloblastoma: Shows features of both Desmoplastic variant & classic follicular ameloblastoma. It is probably a transitional form of desmoplastic ameloblastoma.

Clinical features:

  • Benign, locally infiltrative, epithelial neoplasm.
  • A variant or sub-type of SMA.
  • Painless swelling: chief complaint in most cases.

Radiographic features:

  • Well defined borders are usually not seen.
  • Mixed radiolucent/ radiopaque in most cases.
  • Root resorption is common.
  • New bone formation may be seen.
  • Shows infiltration in adjacent bone marrow space. It causes ill-defined borders of lesion.


  • 4-13% of all SMA
  • Age – 17-72yrs (43yrs)
  • Slight or no male predominance.
  • Occurs with almost equal frequency in both jaws. More common in Anterior region.



  • Consists of proliferating, irregular, often bizarrely shaped islands and cords of odontogenic epithelium of varying sizes embedded in a desmoplastic connective tissue stroma.

Epithelial islands: 

  • Irregular in shape and have a pointed stellate appearance.
  • Pathognomonic animal like outline.
  • Peripheral epithelial cells are usually cuboidal, rarely columnar with reversal of polarity.
  • Hyperchromatic nuclei may be seen sometimes.

Centre of epithelial islands:

  • Hypercellular with spindle shaped or squamatoid or rarely keratinized epithelial cells.
  • Microcysts containing eosinophilic amorphous deposits or empty are common within tumour islands.
  • Foci of keratinization may be seen sometimes.
  • Glandular differentiation with mucous cells formation may be seen in tumour nests.

Connective tissue stroma:

  • Extensive stromal dysplasia.
  • Moderately cellular, fibrous connective tissue.
  • Collagen fibres are thick & numerous. They appear to compress tumour islands.
  • Myxoid changes may be seen in stroma around odontogenic epithelium.
  • Metaplastic bone formation may be seen.
  • Capsule – peripheral fibrous condensation not always seen.


Same as SMA        


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