Liposarcoma

Liposarcoma is a malignant mesenchymal neoplasm showing adipose differentiation.[1][2] It is the most common soft tissue sarcoma in adults at extracranial sites, accounting for approximately 15–20% of all soft tissue sarcomas, but is exceedingly rare in the oral and maxillofacial region.[1][3][4] Oral liposarcomas represent roughly 0.3% of all sarcomas at this anatomic site.[1] The tumor arises from mesenchymal progenitor cells capable of adipocytic differentiation; the pathogenesis varies by subtype and involves distinct genetic aberrations including 12q13-15 amplification (well-differentiated/dedifferentiated subtypes) and specific chromosomal translocations (myxoid subtype).[4][5][6] In the oral cavity, liposarcoma characteristically presents as a slowly enlarging, painless soft tissue mass that is commonly mistaken clinically for a benign lipoma or fibroma.[1][7][8] Imaging typically reveals a soft tissue mass with variable fat content depending on histologic subtype. Complete surgical excision is the mainstay of treatment, and oral liposarcomas generally carry a more favorable prognosis than those at other body sites.[2][7]

The 2020 WHO Classification of Soft Tissue and Bone Tumours recognizes four principal liposarcoma subtypes:[4][6]

• Atypical lipomatous tumor / well-differentiated liposarcoma (ALT/WDLPS) — the terms ALT and WDLPS are synonymous; ALT is preferred for tumors in surgically accessible locations (extremity, trunk) where complete excision is feasible, while WDLPS is used for retroperitoneal or other deep-seated sites[4][9]
• Dedifferentiated liposarcoma (DDLPS)
• Myxoid liposarcoma — the former "round cell liposarcoma" is now considered the high-grade (hypercellular) end of the myxoid liposarcoma spectrum rather than a separate entity[4][5]
• Pleomorphic liposarcoma
• Myxoid pleomorphic liposarcoma — a recently recognized, rare subtype added in the 2020 classification[6]

The obsolete term "mixed-type liposarcoma" has been removed from the classification, as such cases are now considered dedifferentiated liposarcoma with myxoid change.[4] The historical term "liposarcoma circumscriptum" was occasionally used for well-differentiated oral lesions but is no longer in standard use.[10]

• Age: Peak incidence in the fifth to seventh decades; mean age approximately 52 years in oral cavity series[1][7]
• Sex: Slight male predominance (male-to-female ratio approximately 1.1–1.3:1)[1][7][11]
• Frequency: Extremely rare in the oral cavity. Head and neck liposarcomas constitute roughly 5–9% of sarcomas in that region; oral cavity liposarcomas represent only about 0.3% of all oral sarcomas[1][3]
• Anatomic distribution in the oral cavity: The tongue is the most commonly affected site, followed by the buccal mucosa/cheek. Less common locations include the floor of mouth, palate, gingiva, lips, and soft tissue overlying the mandible. Involvement of the jaw bones is exceptionally rare, with only isolated case reports of maxillary osteolysis[1][7][12][13]
• Subtype distribution in the oral cavity: Well-differentiated liposarcoma is the most common subtype (approximately two-thirds of cases), followed by myxoid, dedifferentiated, and pleomorphic subtypes[1][2]

Presentation and Symptoms

Oral liposarcoma typically presents as a slowly growing, painless, soft, submucosal mass.[1][2][8] The mean evolution time before diagnosis is approximately 22 months, reflecting indolent behavior.[1] The overlying mucosa is commonly normal-colored or yellow; ulceration is rare.[1] Mean tumor size at presentation is approximately 2.8 cm (range 0.5–12 cm).[1][7]

Examination Findings

• Soft, compressible, ill-defined swelling that may be mobile
• Normal-colored or yellowish mucosal surface
• Occasional firmness when dedifferentiated or high-grade components are present

Tempo and Complications

Low-grade (well-differentiated) tumors grow slowly and may be present for years before diagnosis, often leading to clinical misdiagnosis as lipoma or fibroma.[1][8] Higher-grade subtypes (dedifferentiated, pleomorphic) may exhibit more rapid growth. Bone involvement is exceptional; one reported case presented with maxillary osteolysis as the initial symptom.[13] Gingival and periodontal involvement has been documented but is very uncommon.[2][12] Regional lymph node metastasis is essentially absent in oral liposarcoma series.[1]

Red Flags

A rapidly enlarging fatty-appearing oral mass, particularly in a middle-aged or older adult, should raise suspicion for liposarcoma rather than benign lipoma, especially if the mass is deep-seated, firm, or larger than expected for a simple lipoma.[8][14]

Oral liposarcoma is predominantly a soft tissue neoplasm; conventional dental radiographic findings are uncommon and typically reflect secondary effects on adjacent osseous structures rather than a primary intraosseous process.

Location and Distribution

• Oral liposarcomas arise in the soft tissues of the tongue, buccal mucosa, floor of mouth, palate, or gingiva[1][7]
• Primary intraosseous liposarcoma of the jaws has not been convincingly documented; jaw involvement occurs only as rare secondary extension or, exceptionally, as metastatic disease[13][15][16]
• On panoramic radiography, the lesion is rarely detected unless it produces secondary osseous changes

Periphery and Shape

• When osseous involvement is present, the margins are characteristically ill-defined and irregular, reflecting an infiltrative soft tissue process eroding into bone[1][13][17]
• One reported palatal case showed a radiolucent area with relatively sharp margins on panoramic radiography, an atypical finding[17]

Internal Architecture

• On panoramic radiography, secondary osseous involvement appears as a radiolucent area without internal mineralization[13][17]
• Calcification or ossification within the soft tissue mass is rare in oral liposarcoma, unlike some extremity liposarcomas where calcifications may occasionally be seen[16][18]

Effects on Teeth and Adjacent Structures

• Tooth displacement and loosening may occur when the tumor involves the alveolar process or periodontal tissues[12]
• Root resorption has been described in cases with gingival or periodontal involvement[12]
• Cortical erosion or osteolysis of the maxilla or mandible is rare and indicates locally aggressive or advanced disease[13]

Growth Pattern and Cortical Involvement

• The tumor typically expands within soft tissues, displacing rather than invading bone in most cases
• When cortical involvement occurs, it manifests as pressure erosion or frank osteolysis with ill-defined borders[13][15]

Subtype-Related Imaging Variations on Cross-Sectional Dental Imaging

The imaging appearance varies substantially by histologic subtype, which is relevant when CBCT or cross-sectional imaging is obtained:

• Well-differentiated liposarcoma: Predominantly fatty mass (characteristically >75% fat content) with thick septa (>2 mm) and small nodular non-adipose areas; the fatty component appears as low-density regions similar to subcutaneous fat. Thick or nodular septa and non-adipose nodular components distinguish this subtype from benign lipoma[16][19][20][21][22]
• Myxoid liposarcoma: Predominantly non-fatty, with high water content producing low-density soft tissue attenuation; small foci of intralesional fat may be identified as a diagnostic clue[16][19][23]
• Dedifferentiated liposarcoma: Contains both fatty (well-differentiated) and non-fatty (dedifferentiated) components; a dominant non-lipomatous nodule >1 cm within a fatty mass is characteristic and should prompt biopsy of the non-adipose component[16][19]
• Pleomorphic liposarcoma: Heterogeneous soft tissue mass with minimal or no macroscopic fat; imaging appearance is nonspecific and overlaps with other high-grade sarcomas[16][23]

Panoramic Radiography Limitations

Panoramic radiography has limited sensitivity for detecting oral liposarcoma, as the tumor is primarily a soft tissue lesion. It was used in fewer than 5% of reported cases.[1] Its role is confined to identifying secondary osseous changes such as alveolar bone loss, cortical erosion, or tooth displacement when the tumor abuts the jaws.

CT

Contrast-enhanced CT is valuable for assessing tumor extent, bone involvement, and relationship to adjacent structures.[1][24] Fat-containing components appear as low-attenuation areas (negative Hounsfield units in well-differentiated subtypes), while myxoid components show near-fluid attenuation (0–20 HU).[19][25] Dedifferentiated and pleomorphic subtypes demonstrate heterogeneous soft tissue attenuation with variable enhancement.[16][23] CT is complementary to MRI for evaluating cortical bone erosion.[24]

MRI

MRI is the preferred modality for primary site evaluation of head and neck soft tissue sarcomas.[6][24] Key subtype-specific features include:

• Well-differentiated: T1 hyperintense (following fat signal), with thick septa and nodular areas that are T2 hyperintense and enhance after gadolinium administration[19][26]
• Myxoid: T1 hypointense (isointense to muscle) with marked T2 hyperintensity reflecting high water content; characteristic linear or nodular T1 hyperintense foci ("marble-like appearance") represent small amounts of intralesional fat; "feathery" enhancement pattern[19][27]
• Dedifferentiated: Mixed signal with lipomatous and non-lipomatous components; the non-lipomatous component shows heterogeneous enhancement[19]
• Pleomorphic: Heterogeneous mass, T1 isointense to muscle, T2 hyperintense; small amounts of fat may be detected on MRI in the majority of cases, suggesting the diagnosis[16][26]

MRI is also preferred for assessing bone marrow invasion, perineural spread, and skull base involvement when relevant.[24]

FDG-PET/CT

FDG-PET/CT may assist in differentiating well-differentiated from dedifferentiated liposarcoma by identifying metabolically active non-lipomatous components, and is useful for staging in higher-grade subtypes.[6][19] For myxoid liposarcoma specifically, whole-body MRI is preferred over PET/CT for detecting extrapulmonary metastases, as PET may underestimate disease burden.[6]

The clinical and imaging differential diagnosis of oral liposarcoma centers on distinguishing it from other soft tissue masses that may contain fat or present as painless submucosal swellings. Because oral liposarcoma is rare and frequently mimics benign lesions, a high index of suspicion is required.

The highest-risk diagnostic pitfall is misclassifying a well-differentiated liposarcoma as a benign lipoma, which may lead to inadequate excision and subsequent local recurrence or dedifferentiation. Any deep-seated, large (>5 cm), or septated fatty oral mass in a middle-aged or older adult warrants excisional or incisional biopsy with histopathologic and, when indicated, molecular confirmation.[8][20][21]

Microscopic Features by Subtype

• Well-differentiated liposarcoma: Mature adipocytic proliferation with significant variation in adipocyte size, focal nuclear atypia and hyperchromasia, scattered hyperchromatic multinucleated stromal cells, and variable numbers of lipoblasts. Irregular fibrous septa contain atypical stromal cells. Variants include lipoma-like (adipocytic), sclerosing, inflammatory, and spindle cell forms[2][4][9]
• Myxoid liposarcoma: Lobular growth pattern with a prominent myxoid stroma containing a delicate, branching ("chicken-wire") capillary vasculature. Small lipoblasts and primitive mesenchymal cells are set in the myxoid background. Hypercellular (round cell) areas indicate high-grade progression[4][15][19]
• Dedifferentiated liposarcoma: Transition from a well-differentiated component to a non-lipogenic, high-grade sarcoma that may show pleomorphic, spindle cell, or heterologous differentiation (e.g., rhabdomyoblastic, chondro-osseous)[4][9][30]
• Pleomorphic liposarcoma: High-grade pleomorphic sarcoma containing multivacuolated lipoblasts; no pathognomonic genetic alteration[4][5]

Immunohistochemistry and Molecular Diagnostics

• S-100 protein and vimentin are commonly expressed across subtypes[1]
• MDM2 and CDK4 nuclear immunoexpression is characteristic of well-differentiated and dedifferentiated subtypes, reflecting amplification of the 12q13-15 chromosomal region. The combined sensitivity and specificity of MDM2/CDK4 immunohistochemistry for identifying WDLPS/DDLPS are high (>90% sensitivity, >83% specificity), though FISH for MDM2 amplification remains the confirmatory standard in histologically ambiguous cases[1][6][31][32][33]
• Myxoid liposarcoma harbors a pathognomonic translocation: t(12;16)(q13;p11) producing the FUS::DDIT3 fusion (most common) or t(12;22)(q13;q12) producing EWSR1::DDIT3[6][34]
• Pleomorphic liposarcoma shows complex karyotypic alterations without a specific recurrent genetic marker[5][6]

Radiologic-Pathologic Correlation

The imaging appearance directly reflects histologic composition: the proportion of mature fat, myxoid stroma, and cellular (non-lipogenic) components determines the density and signal characteristics on cross-sectional imaging.[16][23] Well-differentiated tumors with abundant fat are most readily identified on imaging, while myxoid and pleomorphic subtypes may lack macroscopic fat and mimic non-adipocytic lesions.[16]

Workup and Referral

Any suspected oral liposarcoma requires referral to a multidisciplinary team including oral and maxillofacial surgery and surgical oncology.[6][14] Incisional or core needle biopsy with histopathologic examination is essential for definitive diagnosis; immunohistochemistry for MDM2/CDK4 and molecular testing (FISH or NGS) should be performed when subtype classification is uncertain.[1][6][31] Cross-sectional imaging (MRI preferred) is indicated for preoperative assessment of tumor extent and relationship to adjacent structures.[6][24]

Definitive Treatment

• Surgical excision is the mainstay of treatment for all subtypes of oral liposarcoma. Complete excision with oncologically appropriate margins is the goal; radical surgery with adequate margins is associated with the best outcomes[1][2][7][11]
• Radiation therapy has a limited and controversial role in oral liposarcoma. It is generally reserved for cases with positive margins, recurrent disease, or high-grade subtypes where re-excision is not feasible. Myxoid liposarcoma is uniquely radiosensitive among the subtypes[2][6][11][19][35]
• Systemic chemotherapy plays a minimal role in primary oral liposarcoma management and is typically reserved for unresectable, metastatic, or recurrent high-grade disease[6][35]

Recurrence and Metastasis

• Local recurrence occurs in approximately 15–20% of oral liposarcoma cases and is strongly associated with incomplete initial excision[1][2][7]
• Distant metastasis is uncommon in oral liposarcoma (reported in approximately 2% of cases), with the lungs and parotid gland being the most commonly affected sites[1]
• Regional lymph node metastasis is essentially absent[1]

Prognosis

• Overall 5-year survival for oral liposarcoma is approximately 66%, which is relatively favorable compared with other malignancies[1][11]
• Prognosis is principally determined by histologic subtype and grade: well-differentiated tumors carry the best prognosis (approaching 100% 5-year survival), while pleomorphic and round cell subtypes have significantly worse outcomes[11]
• Oral and salivary gland liposarcomas appear to have a better prognosis than liposarcomas at other body sites, likely due to smaller size at presentation and predominance of well-differentiated histology[7]
• Independent prognostic factors include treatment modality.