Overview and definition
Odontogenic myxoma is a benign but locally aggressive mesenchymal odontogenic neoplasm derived from odontogenic ectomesenchyme.[1][2] It ranks among the three most common odontogenic tumors after odontoma and ameloblastoma.[1][3] The tumor is characterized by an unencapsulated, infiltrative growth pattern within the tooth-bearing areas of the jaws, with a strong predilection for the posterior mandible.[1] Its signature radiographic pattern is a multilocular radiolucency with fine, straight or angular internal septa producing "tennis racket," "honeycomb," or "soap bubble" configurations.[4][5] Management centers on surgical excision; the infiltrative nature of the tumor necessitates removal with a margin of uninvolved bone to minimize recurrence.[1][6]
Terminology and classification
The 5th edition WHO Classification of Head and Neck Tumours (2022) lists odontogenic myxoma under benign mesenchymal odontogenic tumors.[3] The term odontogenic fibromyxoma (also myxofibroma or fibromyxoma) designates a histologic variant with a prominent collagenous stromal component.[7][8] Both are considered part of a single tumor spectrum; the fibrous tissue proportion shows a bimodal distribution with a threshold near 45% separating predominantly myxoid from predominantly fibrous lesions.[8][9] Earlier WHO editions (2005, 2017) similarly classified the tumor as a benign mesenchymal odontogenic neoplasm.[10][11] The shortened form "myxoma of the jaws" appears in older literature but is now discouraged because it obscures the odontogenic origin.
Epidemiology
- Age: Mean age at diagnosis is approximately 28–29 years, with peak incidence in the second through fourth decades. The reported range extends from infancy to the eighth decade.[1][2]
- Sex: Female predominance, with a female-to-male ratio of approximately 1.4:1 to 1.8:1 across large series.[1][3]
- Frequency: Odontogenic myxoma constitutes roughly 3–15% of all odontogenic tumors depending on the population studied, with higher relative frequencies reported in some African and Asian series.[3][12]
- Anatomic distribution: The mandible is affected more often than the maxilla (approximately 56–70% mandibular). Posterior regions predominate in both jaws. Approximately 47% of maxillary lesions significantly involve the maxillary sinus. Extension to the coronoid or condylar process is uncommon. Midline crossing occurs in roughly 7% of cases.[1][13]
- A rare peripheral (extraosseous) variant presents as a gingival soft-tissue mass without bony involvement.[13]
Clinical presentation
Most odontogenic myxomas are asymptomatic at presentation, discovered incidentally on routine radiographs; only about 17% of patients report symptoms.[1][14] The most common clinical finding is painless bony expansion or jaw swelling.[1][13] Bone expansion is present in over 90% of cases with available data.[1]
Symptoms and signs
- Slow, progressive, painless swelling of the affected jaw region
- Tooth mobility, displacement, or failure of eruption in the involved area[1][15]
- Occasional mild pain or paresthesia when the inferior alveolar nerve is compressed
- Maxillary lesions may present with unilateral nasal obstruction or fullness rather than visible swelling, because the tumor can expand silently into the maxillary sinus[6]
Tempo and complications
Growth is typically slow but relentless. Cortical perforation is common (approximately 75% of cases) yet often clinically silent.[1] Large tumors may cause facial asymmetry, malocclusion, or pathologic fracture. Malignant transformation has not been documented.
Radiographic findings
The radiographic appearance of odontogenic myxoma is variable and depends on lesion size, location, and the proportion of myxoid versus fibrous stroma.[5][14]
Location and distribution
- Strong predilection for the posterior mandible (body, angle, ramus), followed by the posterior maxilla[1]
- Lesions arise in tooth-bearing or formerly tooth-bearing regions, consistent with odontogenic ectomesenchymal origin
- Maxillary tumors frequently extend into the maxillary sinus; nearly half of maxillary lesions show significant sinus involvement[1][16]
- Large mandibular lesions may extend into the ramus, reaching the coronoid or condylar process[1]
Periphery and shape
- Margins range from well-defined and corticated (more common in the mandible, ~80% of mandibular cases) to ill-defined and blending with adjacent bone (more common in the maxilla, where only ~33% are well-defined)[14][16]
- Shape is variable: round, ovoid, or irregular, conforming to the available anatomic space
- Scalloped margins are common, particularly when the lesion extends between tooth roots[4][17]
Internal architecture
The internal structure is the most diagnostically useful feature:
- Multilocular radiolucency is the predominant pattern on conventional radiographs (~57–63% of cases), while smaller lesions may appear unilocular (~33–37%)[1][2]
- Characteristic fine, straight or angular septa divide the lesion into triangular, square, or rectangular compartments, producing the classic "tennis racket" or "honeycomb" pattern[4][5]
- Coarser, curved septa create a "soap bubble" appearance in some cases[5][17]
- Septa frequently concentrate at the periphery of the lesion and may appear perpendicular to the cortical margin; in some cases this produces a "sunray" spiculated pattern at the periphery on cross-sectional imaging[4][18]
- The honeycomb pattern on conventional radiographs is more commonly seen in larger mandibular lesions[15]
- Angular septa, although suggestive of odontogenic myxoma, are present in only about 35% of cases and are not required for the diagnosis[1]
- On volumetric imaging, the internal density of the tumor is typically lower than that of surrounding muscle, reflecting the high water content of the myxoid matrix[19]
Effects on teeth and adjacent structures
- Tooth displacement and/or failure of eruption is common, reported in approximately 54% of cases[1]
- Root resorption occurs in roughly 19–20% of cases—less frequent than with ameloblastoma—and tends to be smooth and gradual[1][15]
- The tumor characteristically scallops between tooth roots and involves the alveolar process, disrupting the integrity of the alveolar ridge[4]
- Widening of the periodontal ligament space of adjacent teeth may be an early sign[20]
Cortical involvement and growth pattern
- Cortical expansion is nearly universal (>93%)[1]
- Cortical perforation is common (~75%), often asymptomatic, with the tumor extending into adjacent soft tissues[1][4]
- The expanded cortex may appear thinned and discontinuous, with soft-tissue bulging beyond the bony contour[4][18]
- Maxillary lesions may erode the sinus floor, orbital floor, or nasal cavity walls with minimal external swelling[6][21]
Recognized variants and atypical presentations
- Small, early lesions may present as a subtle interradicular radiolucency with mild tooth displacement, mimicking a periapical or periodontal lesion[15][22]
- Rare cases show a mixed radiolucent-radiopaque pattern with foci of osteogenesis[5]
- Unilocular lesions without septa can closely mimic dentigerous cysts or unicystic ameloblastoma, particularly in pediatric patients[22]
Other imaging findings
MRI features
MRI provides superior soft-tissue contrast for delineating tumor extent, particularly in maxillary lesions with sinus, orbital, or skull-base proximity.[23][24]
- T1-weighted images: intermediate signal intensity throughout the tumor[20][24]
- T2-weighted images: homogeneous high signal intensity, reflecting the abundant myxoid (mucopolysaccharide-rich) matrix[20][24]
- Gadolinium-enhanced T1-weighted images: peripheral rim enhancement corresponding to the collagenous capsule-like zone, with minimal or absent enhancement of the central myxoid portion[20][24]
- Dynamic contrast-enhanced MRI: gradual, progressive enhancement over 500–600 seconds distinguishes odontogenic myxoma from ameloblastoma, which shows rapid early enhancement with plateau or washout[25]
These MRI characteristics help differentiate odontogenic myxoma from ameloblastoma (which typically shows cystic compartments with water-like signal and solid enhancing nodules) and from odontogenic cysts (which lack solid enhancing components).[20][25]
Differential diagnosis
The differential diagnosis of odontogenic myxoma centers on other multilocular or expansile radiolucent jaw lesions arising in the posterior jaws of young adults. Small unilocular lesions broaden the differential to include cystic entities.
| Entity | Why it is considered | Best discriminator |
|---|---|---|
| Ameloblastoma | Multilocular radiolucency in the posterior mandible of a young adult with cortical expansion | Ameloblastoma shows coarser, curved septa ("soap bubble") rather than fine straight angular septa; root resorption is more frequent; MRI reveals cystic compartments with water-signal intensity rather than homogeneous high T2 signal[1][4][20] |
| Odontogenic keratocyst | Unilocular or multilocular posterior mandibular radiolucency, may scallop along the ramus | Odontogenic keratocyst grows along the medullary cavity with less buccal-lingual expansion and less cortical perforation; aspiration yields thin keratinaceous fluid[1][26] |
| Central giant cell granuloma | Multilocular radiolucency crossing the midline in the anterior mandible of a young patient | Anterior location, wispy septa, and younger age profile differ from the posterior predilection and angular septa of odontogenic myxoma; serum calcium and PTH exclude brown tumor[20][26] |
| Ameloblastic fibroma | Mixed odontogenic tumor in a child or adolescent with a well-defined multilocular radiolucency | Ameloblastic fibroma occurs at a younger mean age and contains characteristic ameloblastic epithelium with peripheral palisading on histology[27] |
| Dentigerous cyst | Well-corticated unilocular pericoronal radiolucency associated with an unerupted tooth | Attachment at the cementoenamel junction, uniformly corticated margin, and absence of internal septa distinguish dentigerous cyst; small unilocular odontogenic myxomas in children may closely mimic this entity[22][26] |
The highest-risk diagnostic pitfall is misidentifying a small, unilocular odontogenic myxoma as a dentigerous cyst or hyperplastic dental follicle in a pediatric patient, leading to inadequate curettage and subsequent recurrence.[6][22] When clinical and radiographic features are ambiguous, incisional biopsy is essential before definitive surgery.
Histopathology
Microscopic features
- Stellate and spindle-shaped cells with slender cytoplasmic processes dispersed in an abundant myxoid (mucoid) extracellular matrix rich in glycosaminoglycans (heparan sulfate, chondroitin sulfate)[1][17]
- Nuclei are bland, round to fusiform; minor nuclear atypia, hyperchromasia, and rare mitoses may be present but do not indicate malignancy[17]
- The tumor is unencapsulated and infiltrative, with residual bony trabeculae "floating" within the myxoid stroma—a feature that correlates with the radiographic septal pattern[6][28]
- Sparse islands or strands of odontogenic epithelium resembling rests of Malassez are present in approximately 13% of cases; these are incidental and carry no diagnostic or prognostic significance[1][6]
Fibromyxoma variant
When the collagenous component is prominent (fibrous tissue proportion exceeding ~45%), the lesion is designated odontogenic fibromyxoma.[8][9] Fibromyxoma may show a tendency toward less cortical perforation and more frequent unilocular radiographic morphology compared with predominantly myxoid tumors.[8][9]
Radiologic-pathologic correlation
The fine internal septa on imaging correspond to residual bony trabeculae entrapped by the infiltrating myxoid tumor.[28] The low density on CT and high T2 signal on MRI reflect the hydrated mucopolysaccharide-rich stroma.[19][24] Peripheral enhancement on contrast-enhanced imaging corresponds to the collagen-rich zone at the tumor margin.[24]
Key diagnostic pitfalls
- Dental papilla and dental follicle contain myxoid tissue that can be mistaken for odontogenic myxoma; correlation with clinical and radiographic context (presence of a developing tooth germ) is essential[6][17]
- Maxillary lesions extending into the sinus may be misinterpreted as nasal polyps on biopsy[6]
- Myxoid change in other neoplasms (nerve sheath tumors, low-grade fibromyxoid sarcoma, chondromyxoid fibroma) must be excluded by immunohistochemistry and clinical context[27]
Immunohistochemistry and molecular findings
Tumor cells are uniformly positive for vimentin and commonly express Bcl-2.[13] Ki-67 positivity is variable.[13] GNAS mutations, characteristic of fibrous dysplasia and some soft-tissue myxomas, are absent in odontogenic myxoma.[28][29] Recent methylation profiling has identified a distinct DNA methylation signature with recurrent whole-chromosome gains (trisomies of chromosomes 5, 8, and 20 in all cases studied; chromosomes 10, 12, and 17 in most).[30] A subset of tumors harbor KRAS mutations, suggesting possible involvement of the MAPK/ERK pathway, though sample sizes remain small.[31][32]
Management and prognosis
Surgical treatment
Surgical excision is the standard treatment. The choice of procedure depends on tumor size, location, locularity, and proximity to vital structures.[1][33]
- Enucleation with peripheral ostectomy is recommended as the first-line approach for most lesions, balancing adequate tumor removal with preservation of jaw continuity; recurrence with this technique is approximately 7%[1][14]
- Curettage alone carries the highest recurrence rate (~31%) and is generally inadequate[1]
- Marginal resection (1.3% recurrence) and segmental resection (3.1% recurrence) offer the lowest recurrence rates and are indicated for large, multilocular, or recurrent tumors and for maxillary lesions with poorly defined margins[1]
- Maxillary tumors warrant particular attention because ill-defined margins and proximity to the orbit, skull base, and paranasal sinuses may necessitate more aggressive resection[16][21]
Recurrence
- Overall recurrence rate is approximately 9–13% across pooled data, depending on treatment modality and follow-up duration[1][2]
- No radiographic or histopathologic variable (locularity, angular septa, cortical perforation, epithelial rests) has been shown to predict recurrence significantly[1]
- Maxillary lesions may have a higher recurrence tendency due to delayed detection and less well-defined surgical margins[33]
- Most recurrences present within the first 2 years, but late recurrences have been documented; long-term clinical and radiographic surveillance is recommended[7]
Prognosis
Odontogenic myxoma does not metastasize and has no documented potential for malignant transformation. Morbidity relates to local destruction, surgical defects, and the need for reconstruction. Quality-of-life considerations (disfigurement, neural deficit) are more common after resection than after conservative surgery, supporting a graduated surgical approach.[33]