Ameloblastoma pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Shivali Marketkar, M.B.B.S. [2]

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Overview

On gross pathology, the characteristic findings of ameloblastoma may include solid and cystic, multicystic and intraosseous or extraosseous, or rarely unicystic.On microscopic histopathological analysis, stellate reticulum, giant cells, subepithelial hyalinization, and columnar basal cells in palisading arrangement with vacuolated cytoplasm are characteristic findings of ameloblastoma. The exact pathophysiology of ameloblastoma is not fully understood. It is thought that ameloblastoma is the result of either suppression of matrix metalloproteinase-2 that may inhibit the local invasiveness of ameloblastoma, or there is also some research suggesting that α5β1 integrin may participate in the local invasiveness of ameloblastoma. Genes involved in the pathogenesis of ameloblastoma include BRAF V600E.

Pathophysiology

Pathogenesis

• Ameloblastoma arise from remnants of ameloblast or dental lamina, dentigerous cysts, or basal layer of oral mucosa.
• Ameloblasts, which are part of the odontogenic epithelium, are responsible for enamel production and eventual crown formation.
• There is evidence that suppression of matrix metalloproteinase-2 may inhibit the local invasiveness of ameloblastoma, however, this was only demonstrated in vitro.
• There is also some research suggesting that α5β1 integrin may participate in the local invasiveness of ameloblastomas.
• The ameloblastoma is an ectodermal odontogenic tumor of the jaws which apparently originates from the Malassez rests in the periodontium, from the gingival epithelium, from the enamel organs, or from ordinary dental cysts (dentigerous cysts, follicular cysts, or radicular cysts).

Genetics

A recent study discovered a high frequency of BRAF V600E mutations in solid/multicystic ameloblastoma. These data suggests drugs targeting mutant BRAF as potential novel therapies for ameloblastoma.

Gross Pathology

On gross pathology the following are the characteristic findings of ameloblastoma:

• Solid and cystic
• Multicystic and intraosseous or extraosseous
• Rarely may be unicystic.
• Shown below is the gross specimen of resected left half of mandible initiated at third molar.

Microscopic Pathology

• Stellate reticulum - star-shaped cells, found in a developing tooth
• Giant cells may or may not be present
• Subepithelial hyalinization may or may not be present
• Seen deep to the basement membrane
• Suprabasal cells loosely textured and noncohesive, resembling stellate reticulum
• The plexiform type has epithelium that proliferates in a "Fish Net Pattern"
• The follicular type will have outer arrangement of columnar or palisaded ameloblast like cells and inner zone of triangular shaped cells resembling stellate reticulum in bell stage. The central cells sometimes degenerate to form central microcysts
• No enamel or dentin formation
• Tall columnar cells
  • Palisaded nuclei with reverse polarization
    • Reverse polarization of nuclei = nuclei distant from the basement membrane/nuclei at pole opposite of basement membrane
    • Palisaded nuclei = picket fence appearance; columnar-shaped nuclei with long axis perpendicular to the basement membrane -- key feature
  • Subnuclear vacuolation
• The following are the different histopathological variants of ameloblastoma:
  • Intraosseous (follicular, plexiform, acanthomatous, multicystic, unicystic, granular cell [lysosomes by EM], basal cell, desmoplastic)
  • Extraosseous (follicular, plexiform, basal cell)

Shown below is a micrograph of ameloblastoma

The image shows the characteristic features:

• Islands of cells with palisaded nuclei that have reverse polarization.
• Reverse polarization of nuclei : nuclei distant from the basement membrane/nuclei at pole opposite of basement membrane.
• Palisaded nuclei :picket fence appearance; columnar-shaped nuclei with long axis perpendicular to the basement membrane.

• Subnuclear vacuolation in palisading cell - vacuoles at the basement membrane aspect.
• Loose stroma around the islands of cells.
• Star-like cells at the centre of the islands of cells (stellate reticulum).

Video

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  intermediate magnification showing ameloblastoma