Dx: Odontogenic Myxoma

KEY FACTS

Terminology

Definition: Benign tumor of odontogenic ectomesenchyme

Imaging

Mandible > maxilla; premolar-molar regions

Unilocular or multilocular radiolucency with thin, straight internal septa Septa may form right angles or geometric shapes In larger lesions, septa may be coarse, curved ("soap bubble") and mimic ameloblastoma

Borders may be well defined or ill defined; if well defined, often lobular or scalloped

Top Differential Diagnoses

Ameloblastoma

Central giant cell granuloma

Aneurysmal bone cyst

Central hemangioma

Osteosarcoma

Clinical Issues

Uncommon; only 3-6% of odontogenic tumors

Wide age range; average 25-30 years

No gender predilection

May demonstrate rapid growth and expansion

Infiltrates surrounding bone; does not metastasize

Treatment: Curettage for small lesions Extensive resection for large lesions Complete removal difficult with 25% recurrence rate: Follow-up required for at least 5 years

Diagnostic Checklist

Look for thin cortical margin to rule out osteosarcoma when pseudoperiosteal reaction present

TERMINOLOGY

Synonyms

Myxoma, myxofibroma, fibromyxoma

Definitions

Benign tumor of odontogenic ectomesenchyme

IMAGING

General Features

Best diagnostic clue: Multilocular radiolucency with thin, often straight, internal septa at right angles

Location Any area of jaws; mandible > maxilla (3:1) Most common in premolar-molar regions

Size: Variable, depending on when discovered

Imaging Recommendations

Best imaging tool: CT or CBCT: Evaluation of extent & margins

Radiographic Findings

Radiography Small lesion may be unilocular and well defined Larger lesion may be well defined or ill defined Lobular or scalloped edges ± cortication Internal septa often thin: May form right angles with each other or make geometric shapes May be coarse and curved ("soap bubble") and mimic ameloblastoma May extend at periphery in radiating pattern giving pseudoperiosteal reaction If large, may displace teeth; tooth resorption rare

CT Findings

CBCT or bone CT Better determines extent of larger lesions Thin cortical margin helps differentiate from osteosarcoma when pseudoperiosteal reactions are present

MR Findings

T2WI: ↑ signal: Establishes tumor extent

DIFFERENTIAL DIAGNOSIS

Ameloblastoma

Multilocular radiolucency, corticated border, and coarse, curved internal septa ("soap bubble")

Most common in posterior mandible

May displace, resorb teeth

Central Giant Cell Granuloma

Multilocular radiolucency; well defined, noncorticated

Wispy septa, some at right angles to periphery

Painless, expansile; may displace, resorb teeth

Anterior mandible most common; may cross midline

Aneurysmal Bone Cyst

Multilocular radiolucency with well-defined borders that are curved or "hydraulic"

Internal septa wispy, ill defined, some at right angles to periphery

Rapid expansion in posterior mandible typical

Fluid-fluid levels on T2WI MR

Central Hemangioma

Multilocular radiolucency: Corticated or ill defined

May see small compartments internally, similar to large marrow spaces surrounded by coarse trabeculae

Slow enlargement of jaw, may or may not be painful

May produce linear spicules ("sun ray") at periphery

Osteosarcoma

Spiculated periosteal reaction ("sun ray"); cortex not intact

PATHOLOGY

Gross Pathologic & Surgical Features

Not encapsulated

Loose gelatinous consistency; pathognomonic

Microscopic Features

Resembles developing tooth mesenchyme (dental papilla)

Stellate, spindle-shaped, or round cells in abundant loose myxoid stroma

May see small islands of epithelium

CLINICAL ISSUES

Presentation

Most common signs/symptoms May expand bone Slow growing, painless

Demographics

Age: Wide range; average: 25-30 years

Gender: No gender predilection

Epidemiology: Uncommon; only 3-6% of odontogenic tumors

Natural History & Prognosis

Infiltrates surrounding bone but does not metastasize

May demonstrate rapid growth and expansion

Treatment

Curettage for small lesions

Extensive resection for large lesions

Follow-up required for at least 5 years; complete removal difficult with 25% recurrence rate

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls

Look for thin cortical margin to rule out osteosarcoma when pseudoperiosteal reaction present