Odontogenic Myxoma

§ overviewOverview

A benign, locally infiltrative odontogenic tumour of ectomesenchymal origin, composed of loosely arranged stellate and spindle cells in an abundant myxoid extracellular matrix.

§ icdICD Classification

ICD-10 D16.4/D16.5

§ etiologyEtiology

• 01Origin from odontogenic ectomesenchyme (dental follicle, papilla, periodontal ligament)

§ riskRisk Factors

• 01None specific

§ geneticsGenetics & Molecular Biology

• 01MYB and MDM2 pathway abnormalities reported in some series
• 02Not consistently associated with a specific syndrome

§ epidemiologyEpidemiology

3–20% of odontogenic tumours (regional variation). 2nd–4th decade. F > M. Mandible (66%) > maxilla; posterior region most common.

§ pathogenesisPathogenesis

Neoplastic ectomesenchymal cells produce abundant hyaluronic-acid rich myxoid matrix, which infiltrates between bony trabeculae. Absence of a capsule underlies the finger-like invasion and high recurrence rate.

§ clinicalClinical Features

• 01Slow, painless swelling
• 02Loosening or displacement of teeth
• 03Cortical expansion and thinning
• 04Facial asymmetry

§ signsSigns & Symptoms

• 01Egg-shell crackling
• 02Occasional paraesthesia if IAN involved
• 03Rarely painful

§ differentialDifferential Diagnosis

• 01Ameloblastoma
• 02OKC
• 03Central giant cell granuloma
• 04Aneurysmal bone cyst
• 05Central haemangioma
• 06Fibro-osseous lesion

§ criteriaDiagnostic Criteria

• 01Multilocular radiolucency with straight fine septa (tennis-racket / step-ladder / soap-bubble)
• 02Histology: stellate cells in mucoid stroma with sparse collagen

§ histopathHistopathology

• 01Loose myxoid stroma rich in hyaluronic acid/mucopolysaccharide
• 02Stellate, spindle and round cells with fine cytoplasmic processes
• 03Sparse collagen; occasional odontogenic epithelial rests
• 04No capsule — infiltrative border

§ radiographicRadiographic Features

• 01Multilocular radiolucency with characteristic fine straight bony septa forming 'tennis-racket', 'step-ladder', 'honeycomb' or 'soap-bubble' patterns
• 02Displacement or root resorption of adjacent teeth
• 03Cortical thinning / perforation

§ opgOPG Findings

• 01Screening view; note characteristic septation

§ cbctCBCT Findings

• 01Best imaging for delineation of extent, septation pattern, cortical status

§ ctCT Findings

• 01For extensive lesions with soft-tissue involvement

§ mriMRI Findings

• 01T1 hypointense, T2 markedly hyperintense (myxoid content); heterogeneous enhancement

§ investigationsInvestigations

• 01Incisional biopsy (aspiration first to exclude vascular lesion)
• 02CBCT + MRI for surgical planning

§ labsLaboratory Findings

• 01Aspirate: mucinous stringy fluid, low cellularity

§ ihcIHC / Special Stains

• 01Vimentin positive; S-100 focal; smooth muscle actin variable; MIB-1 (Ki-67) low but higher than dental follicle

§ whoWHO Classification

WHO 2022: Benign odontogenic tumour of mesenchymal origin — Odontogenic myxoma (Odontogenic myxofibroma when fibrous component prominent).

§ classificationClassification

• 01Central (intra-osseous) — vast majority
• 02Peripheral (extraosseous) — extremely rare

§ planTreatment Planning

• 01Balance recurrence risk (25% with curettage) against morbidity of resection
• 02Small (< 3 cm) lesions may permit enucleation with peripheral ostectomy in select cases
• 03Large or recurrent lesions → resection with reconstruction

§ treatmentTreatment

• 01Small lesions: aggressive curettage + peripheral ostectomy ± chemical adjunct (Carnoy's)
• 02Medium/large: marginal or segmental resection with 1–1.5 cm bony margin
• 03Immediate or delayed reconstruction (fibula free flap)

§ medicalMedical Management

• 01Nil disease-specific

§ surgicalSurgical Management

• 01Segmental mandibulectomy with reconstruction plate + free fibula/iliac graft
• 02Marginal resection preserving inferior border where feasible

§ reconstructionReconstruction Options

• 01Reconstruction plate + free fibula osseocutaneous flap for continuity defects
• 02Iliac crest graft for smaller marginal defects

§ complicationsComplications

• 01Recurrence
• 02Cortical perforation with soft-tissue infiltration
• 03Pathologic fracture
• 04Facial deformity

§ recurrenceRecurrence Rate

Curettage: 25%; resection: < 10%. Long-term follow-up mandatory.

§ followupFollow-up Protocol

• 01Clinical + OPG every 6 months for 2 years
• 02Annually for 5 years
• 03Selective CBCT/MRI on suspicion of recurrence

§ prognosisPrognosis

Excellent for lifespan; morbidity from recurrence and reconstruction.

§ preventionPrevention

• 01None

§ examKey Examination Points

• 01Multilocular radiolucency with fine straight septa in a young adult
• 02Aspirate first to rule out vascular lesion
• 03Infiltrative — no capsule — high recurrence with curettage

§ revisionQuick Revision Summary

• 01Ectomesenchymal
• 02Mandible > maxilla
• 03Tennis-racket / step-ladder / soap-bubble
• 04Stellate cells + myxoid stroma
• 05No capsule → recurs; resect with margin

§ vivaBDS Viva Questions

• 01Origin of odontogenic myxoma.
• 02Radiographic patterns.
• 03Why does it recur after curettage?
• 04Histology of myxoma.
• 05Aspiration findings.
• 06Differential of multilocular radiolucency.
• 07Treatment options.
• 08Reconstruction after segmental resection.
• 09Follow-up protocol.
• 10MRI features.
• 11Difference between myxoma and myxofibroma.
• 12Sex and age predilection.
• 13Complications of surgery.
• 14Recurrence rate.

§ bdsBDS Professional Examination

• 01Long essay: Differential diagnosis and management of multilocular radiolucencies of the mandible.
• 02Short note: Odontogenic myxoma.

§ fcpsFCPS Residency Questions

• 01Discuss the surgical management and reconstruction options for a 4 cm odontogenic myxoma of the posterior mandible.

§ pearlsClinical Pearls

• 01Multilocular + straight fine septa + stringy aspirate = myxoma until proven otherwise.
• 02Never curette a multilocular radiolucency without aspirating first.

§ mnemonicsMnemonics

• 01Myxoma = Mucin, Mesenchyme, Mandible, Multilocular, Must resect with Margin

§ readingSuggested Reading

• 01Noffke CEE et al. Odontogenic myxoma: review of the literature and report of 30 cases. Br J Oral Maxillofac Surg 2007.
• 02WHO Blue Book 5e (2022).

§ differentialDifferential Comparison

§ mcqsMCQs — Assessment (20)

§ relatedRelated Diseases

References

1. WHO Classification of Head and Neck Tumours, 5e (2022)
2. Neville BW. Oral and Maxillofacial Pathology, 4e
3. Shafer's Textbook of Oral Pathology, 9e
4. Peterson LJ. Contemporary Oral & Maxillofacial Surgery, 7e