Dx: Ameloblastic Fibroma KEY FACTS

Terminology

Synonyms: Soft odontoma, mixed odontogenic tumor, fibroadamantoblastoma, granular cell ameloblastic fibroma

Definition: Benign odontogenic tumor containing ectomesenchyme resembling dental papilla and epithelial strands and nests resembling dental lamina and enamel organ

Imaging

Well-defined, corticated, often expansile radiolucency without evidence of tooth structures or calcifications within

Associated with crown of unerupted tooth (pericoronal) in many cases

Usually posterior mandible of young patients

Unilocular or multilocular radiolucency

CBCT best demonstrates expansion and loculations

Top Differential Diagnoses

If pericoronal: Hyperplastic follicular space, dentigerous cyst, unicystic ameloblastoma, keratocystic odontogenic tumor (KOT)

If multilocular: Ameloblastoma, central giant cell granuloma, KOT, odontogenic myxoma

Clinical Issues

Slow-growing but can reach large size

Recurrence (~ 33%) higher with curettage, less with radical resection

Malignant transformation reported at ~ 10%

Radiographic follow-up recommended

Diagnostic Checklist

If pericoronal, look for hydraulic expansion to rule out dentigerous cyst (most common)

If small, consider immature odontoma, ameloblastic fibro-odontoma, and ameloblastic odontoma

TERMINOLOGY

Abbreviations

Ameloblastic fibroma (AF)

Synonyms

Soft odontoma

Mixed odontogenic tumor

Fibroadamantoblastoma

Granular cell ameloblastic fibroma

Definitions

Benign odontogenic tumor containing ectomesenchyme resembling dental papilla and epithelial strands and nests resembling dental lamina and enamel organ

IMAGING

General Features

Best diagnostic clue Well-defined, corticated, often expansile radiolucency without calcifications Associated with crown of unerupted tooth (pericoronal) in many cases Usually posterior mandible of young patients

Location

Mandible > maxilla Posterior > anterior

Size: Small to very large (< 1 cm to 16 cm)

Morphology Well-defined unilocular or multilocular radiolucency Typical neoplastic expansion: May form acute angles with remaining cortex

Imaging Recommendations

Best imaging tool CBCT will best show expansion Panoramic and occlusal views

Protocol advice: Bone window

Radiographic Findings

Intraoral plain film Well-defined radiolucency without evidence of hard tissue structures Most often associated with crown of impacted or unerupted tooth (pericoronal) Corticated border

Extraoral plain film Panoramic radiograph will demonstrate expansion in cephalad-caudal direction if present Expansion and thinning of inferior cortex of mandible and external oblique ridge Expansion into maxillary sinus or nasal cavity Loculations may be present

CT Findings

CBCT Demonstrates buccal-lingual expansion Loculations may be more evident Large lesions may perforate buccal and lingual cortices

DIFFERENTIAL DIAGNOSIS

Hyperplastic Follicular Space

Enlarged follicular space around crown of unerupted tooth

Well-defined pericoronal radiolucency

Suspect pathology if pericoronal space > 3 mm

Look for morphology to follow outline of tooth crown

Dentigerous Cyst

Accumulation of fluid between reduced enamel epithelium and crown of unerupted or impacted tooth

Most common pericoronal radiolucency: Well-defined, unilocular

Follicular space takes on more rounded appearance

Hydraulic expansion: Expanded cortex meets normal cortex at equal obtuse angles

May not be able to differentiate if small

Unicystic (Mural) Ameloblastoma

Ameloblastoma arising in wall of cyst (most commonly dentigerous cyst)

Once infiltrates bone, behaves as ameloblastoma:May appear multilocular

Keratocystic Odontogenic Tumor (KOT)

Odontogenic neoplasm with thin para- or ortho-keratinized epithelium

Does not expand significantly in mandible

Can be unilocular, multilocular, or pericoronal

Ameloblastoma

Neoplasm of odontogenic epithelium

Multilocular radiolucency

Posterior mandible

Older age group

Central Giant Cell Granuloma (CGCG)

Reactive nonodontogenic lesion

Usually multilocular and expansile

Predilection for anterior mandible Never pericoronal

Odontogenic Myxoma

Benign neoplasm of odontogenic ectomesenchyme

Multilocular with straight septa making geometric shapes and letters

Immature Odontoma

Hamartoma of odontogenic epithelium and ectomesenchyme

Produces radiopaque/high-density areas consistent with tooth structure

Unilocular

May be completely radiolucent prior to maturation and therefore unable to differentiate

Immature Ameloblastic Fibro-odontoma (AFO)

Mixed odontogenic neoplasm

Produces less calcified tooth structure than odontoma

Immature Ameloblastic Odontoma (AO)

Mixed odontogenic neoplasm

More aggressive than odontoma and AFO

Very rare

PATHOLOGY

General Features

Etiology: Unknown

Genetics: Alteration of p53 gene in malignant transformations

Associated abnormalities Has been reported in association with calcifying odontogenic cyst (Gorlin cyst) Strands of odontogenic epithelium are found in hypercellular connective tissue nodules located in cystic wall

Gross Pathologic & Surgical Features

Encapsulated tumor mass

Microscopic Features

Strands and nests of odontogenic epithelium in immature fibrous connective tissue stroma resembling dental papilla Contains no hard tissue (tooth) structures

Odontoma, ameloblastic fibro-odontoma, and ameloblastic odontoma, which contain tooth structure, may look similar prior to maturation when calcifications may not be radiographically evident

Concept that AF represents immature form of odontoma, AFO, or AO is not supported by current data Several residual and recurrent AFs have not demonstrated further maturation AF is occasionally observed in older age group beyond period of odontogenesis

Malignant transformation to ameloblastic fibrosarcoma occurs in mesenchymal component: Increased cellularity, mitosis, and anaplasia

Epithelial component disappears Rarely metastasizes

Malignant transformation to ameloblastic carcinosarcoma has been reported but is extremely rare Epithelial component is retained and exhibits spectrum from normal palisading ameloblasts to frankly malignant cells showing pleomorphism and hyperchromatic nuclei More likely to occur after multiple resections of AF Metastasis to lungs and regional lymph nodes

CLINICAL ISSUES

Presentation

Most common signs/symptoms Hard swelling of jaws Associated with multilocular lesions Failure of eruption of involved tooth

Other signs/symptoms Occasionally pain &/or drainage Symptomatic patients usually have multilocular lesions

Demographics

Age Childhood/adolescence Mean age ~ 15 years

Gender: Slight male predilection

Natural History & Prognosis

Slow growing but can reach large size

Recurrence (~ 33%) directly related to treatment modality Recurrence higher with more conservative treatment Longer period of nonrecurrence with more radical treatment One study found recurrence rates of 41% and 69% at 5 and 10 years, respectively

Malignant transformation reported at ~ 10% Malignant transformation rate of 10% and 22% at 5 and 10 years respectively Malignant transformation less likely to occur in patients younger than 22 years May recur multiple times and even cause death Distant metastases rare

Treatment

Curettage

Enucleation

Simple excision

Radical resection for larger tumors

Close radiographic follow-up recommended

DIAGNOSTIC CHECKLIST

Consider

Odontoma, AFO, and AO if small In early stages these lesions may be completely radiolucent

Ameloblastoma, central giant cell granuloma, and keratocystic odontogenic tumor if multilocular

Image Interpretation Pearls

If pericoronal, look for hydraulic expansion to rule out dentigerous cyst, which is most common pericoronal radiolucency