Mandible & maxilla

Benign odontogenic tumors

Odontogenic myxoma / fibromyxoma


Editorial Board Member: Molly Housley Smith, D.M.D.
Deputy Editor-in-Chief: Kelly Magliocca, D.D.S., M.P.H.
Abberly Lott Limbach, M.D.

Last author update: 29 November 2023
Last staff update: 29 November 2023

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PubMed Search: Odontogenic myxoma / fibromyxoma

Abberly Lott Limbach, M.D.
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Cite this page: Lott Limbach A. Odontogenic myxoma / fibromyxoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/mandiblemaxillamyxoma.html. Accessed March 29th, 2024.
Definition / general
Essential features
  • Stellate, spindle shaped, round cells arranged haphazardly in abundant, fibrillary myxoid / mucoid stroma with infiltration into surrounding bone
  • Radiolucent lesion with thin, fine, coarse or wispy trabeculae of residual bone arranged perpendicular to one another (tennis racket or soap bubble appearance)
  • Recurrence is common due to infiltrative nature of the neoplasm
Terminology
  • Odontogenic myxoma
  • Odontogenic fibromyxoma
ICD coding
  • ICD-O: 9320/0 - odontogenic myxoma
  • ICD-10
    • D16.4 - benign neoplasm of bones of skull and face
    • D16.5 - benign neoplasm of lower jaw bone
  • ICD-11
    • 2E83.0 & XH48L4 - benign osteogenic tumors of bone or articular cartilage of skull or face & odontogenic myxoma
    • 2E83.1 & XH48L4 - benign osteogenic tumors of bone or articular cartilage of lower jaw & odontogenic myxoma
Epidemiology
Sites
Pathophysiology
Etiology
  • Unknown
Clinical features
Diagnosis
Radiology description
Radiology images

Images hosted on other servers:
Multilocular, radiolucent lesion

Multilocular, radiolucent lesion

Right mandibular lateral occlusal view

Right mandibular lateral occlusal view

Multilocular radiolucent osteolytic lesion

Multilocular radiolucent osteolytic lesion

CT scan of mandible

CT scan of mandible

Prognostic factors
Case reports
Treatment
Clinical images

Images hosted on other servers:
Swelling on the right side

Swelling on the right side

Mandibular right quadrant

Mandibular right quadrant

Gray-white appearance

Gray-white appearance

Gross description
Gross images

Contributed by Kelly Magliocca, D.D.S., M.P.H.
Mandibular myxoma resection

Mandibular myxoma resection



Images hosted on other servers:
Jelly-like appearance

Jelly-like appearance

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Abberly Lott Limbach, M.D. and Kelly Magliocca, D.D.S., M.P.H.
Myxoid background with bland spindle cells

Myxoid background with bland spindle cells

Bland spindle cells in myxoid stroma

Bland spindle cells in myxoid stroma

Inactive odontogenic rests

Inactive odontogenic rests


Maxilla neoplasm

Maxilla neoplasm

Mandibular lesion Mandibular lesion

Mandibular lesion

Mandibular lesion

Mandibular lesion

Virtual slides

Images hosted on other servers:
Odontogenic myxoma in mandible

Odontogenic myxoma in mandible

Positive stains
Molecular / cytogenetics description
Sample pathology report
  • Mandible, segmental resection:
    • Odontogenic myxoma
    • Margins of excision negative
Differential diagnosis
  • Dental papilla or dental follicle:
    • Immature dental pulp or follicle from a developing tooth
    • Often requires clinical and radiographic correlation to differentiate from myxoma
    • Dental papillae may show a rim of odontoblasts
  • Myxoid neurofibroma:
  • Chondromyxoid fibroma:
    • Presence of chondroid / mature cartilaginous component
  • Odontogenic fibroma:
    • More cellular and fibrocollagenous
    • Strands or islands of odontogenic epithelium more prominent
  • Infantile sinonasal myxoma (Am J Surg Pathol 2023;47:1301):
    • Short, intersecting fascicles of bland, stellate to spindle cells
    • Prominent stromal vessels and variably myxoid to collagenous stroma
    • Neoplastic cells exhibited bipolar to stellate, fibroblastic cytomorphology, with pale pink cytoplasm, vesicular nuclei and small, distinct nucleoli
    • Pushing border rather than infiltrative growth
    • No dystrophic calcifications
    • No rests of odontogenic epithelium
    • Mitotic index low (median < 1 per 10 HPF)
    • Strong and diffuse nuclear β catenin in majority of cases, rare SMA positive
    • Negative for S100 protein, CD34 and desmin
    • Molecular level: most tumors harbor CTNNB1 mutations (D32Y, G34E, G34R and I35S) on exon 3 or APC alterations consistent with biallelic inactivation
    • Combination of patient age, tumor site and strong and diffuse nuclear β catenin expression generally distinguished infantile sinonasal myxomas from odontogenic myxoma
Board review style question #1

The tumor shown above is found in the posterior mandible. What is the best diagnosis?

  1. Chondromyxoid fibroma
  2. Intraosseous mucoepidermoid carcinoma
  3. Odontogenic keratocyst
  4. Odontogenic myxoma
Board review style answer #1
D. Odontogenic myxoma. The image shows scant spindle cells in a myxoid background consistent with odontogenic myxoma. Answer B is incorrect because intraosseous mucoepidermoid carcinoma would have an epidermoid component and lack spindle cells. Answer A is incorrect because chondromyxoid fibroma contains cartilage (not seen in the image). Answer C is incorrect because odontogenic keratocyst is lined by a squamous type epithelium and lacks significant myxoid change.

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Reference: Odontogenic myxoma / fibromyxoma
Board review style question #2
Odontogenic myxomas have been shown to have which of the following molecular alterations?

  1. BRAF mutations
  2. GNAS mutations
  3. KRAS mutations
  4. MAPK / ERK pathway activation
Board review style answer #2
D. MAPK / ERK pathway activation. Odontogenic myxomas have been shown to have activation of the MAPK / ERK pathway. Answer A is incorrect because BRAF mutations can be seen in ameloblastomas. Answer B is incorrect because GNAS mutations are seen in fibrous dysplasia. Answer C is incorrect because KRAS mutations can be seen in adenomatoid odontogenic tumors.

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Reference: Odontogenic myxoma / fibromyxoma
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