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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