Mandible & maxilla

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• Recurrence rates are variable, 10 - 43% and related to extent of excision (Head Neck Pathol 2020;14:1021, Eur J Clin Invest 2020;50:e13214)

• 14 year old boy with maxillary mass (BMJ Case Rep 2020;13:e234933)
• 18 year old man with maxillary mass (J Clin Diagn Res 2015;9:ZD29)
• 22 year old woman with right mandibular mass (Head Neck Pathol 2018;12:44)
• 28 year old woman and 36 year old man both with maxillary masses (Contemp Clin Dent 2015;6:131)

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Contributed by Kelly Magliocca, D.D.S., M.P.H.


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Contributed by Abberly Lott Limbach, M.D. and Kelly Magliocca, D.D.S., M.P.H.

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• 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:
  • S100 positive
• 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

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

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

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

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