Calcified chondroid mesenchymal neoplasm

Calcified chondroid mesenchymal neoplasm (CCMN) is a recently recognized benign matrix-forming soft tissue tumor characterized by chondroid/cartilaginous matrix production, distinctive calcification patterns, and frequent FN1 gene fusions with receptor tyrosine kinase partners.[1][2] The entity was first delineated in 2021 and has since been confirmed in nearly 100 reported cases.[3] CCMN shows a strong predilection for the distal extremities (hands, feet, wrists) and the temporomandibular joint (TMJ) region.[2][4] Pathogenesis centers on FN1 rearrangements—most commonly FN1::FGFR2—that activate receptor tyrosine kinase signaling and drive chondroid matrix production.[1][5] On imaging, CCMN presents as a well-circumscribed soft tissue mass with variable internal calcification and an indolent radiologic appearance.[2] Complete excision is curative; no malignant behavior has been documented.[4]

• Calcified chondroid mesenchymal neoplasm (CCMN) is the currently accepted designation, proposed by Liu et al. in 2021 to encompass a spectrum of FN1-rearranged chondroid soft tissue tumors.[1]
• The term was adopted and validated in the largest published series by Kallen et al. (2023, 33 cases) and Benard et al. (2024, 33 cases).[2][5]
• CCMN is not yet included in the 2020 WHO Classification of Soft Tissue and Bone Tumours but is recognized as an emergent entity in the soft tissue pathology literature.[3][6]
• Historically, many CCMNs were classified under soft tissue chondroma (particularly the "chondroblastoma-like" variant), chondroid tenosynovial giant cell tumor, or tophaceous pseudogout, depending on the dominant morphologic pattern.[1][5][6]
• The term "FN1-rearranged calcified chondroid mesenchymal neoplasm" appears in some publications but is considered synonymous.[1]
• Awareness of this entity is critical because CCMNs are frequently referred for expert consultation out of concern for chondrosarcoma, a diagnostic pitfall that may lead to unnecessary aggressive treatment.[2]

• Age: Mean age approximately 51–52 years (range 14–87 years).[2][4]
• Sex: Approximately equal male-to-female distribution.[2][4]
• Frequency: Rare; nearly 100 cases reported since the entity's initial description in 2021.[3]
• Anatomic distribution:
  • Distal extremities (hands, fingers, feet, toes, wrist, forearm) represent the most common site (~80% of cases).[4]
  • TMJ/temporal/parotid region is the second most common location, accounting for approximately 9 of the first 50 well-documented cases.[4]
  • Rare sites include the perineum and other soft tissue locations.[7]
• One case of multifocal disease has been reported.[2]

Presentation and symptoms

• CCMN typically presents as a slowly growing, painless or mildly symptomatic soft tissue mass.[2][4]
• In the extremities, patients may note a firm nodule in the digits, hand, foot, or wrist, often present for months to years before clinical evaluation.[8]
• In the TMJ region, presentation may include:
  • Preauricular swelling or mass
  • TMJ pain or dysfunction
  • Limited mouth opening[4][9]

Examination findings

• Palpation reveals a firm to hard, well-circumscribed nodule.[2]
• Mean gross tumor size is approximately 2.1 cm.[2]
• The cut surface is homogeneous, rubbery to fibrous/gritty, and tan-white.[2]

Tempo and complications

• Growth is characteristically indolent; imaging in all reported cases has appeared benign.[2]
• No malignant transformation, metastasis, or mortality attributable to CCMN has been documented.[3][4]
• The primary clinical concern is misdiagnosis as chondrosarcoma, which may prompt unnecessarily aggressive surgery.[2]

Location and distribution

• In the maxillofacial region, CCMN arises predominantly in the TMJ/temporal/parotid region as an extraosseous soft tissue mass.[3][4]
• Extremity lesions involve the digits, hands, feet, wrists, and forearms.[2][4]
• The tumor is soft tissue–based; it does not arise within bone, though it may abut or scallop adjacent osseous structures.[2]

Periphery and shape

• CCMN presents as a well-circumscribed, lobulated or multinodular soft tissue mass.[2][4]
• Margins are smooth and well-defined, consistent with a benign process.[2]
• No infiltrative or irregular margins have been described in the reported imaging literature.[2]

Internal architecture

• The hallmark radiographic feature is variable internal calcification:[2][4]
  • Calcifications are described as grungy (amorphous, coarse) and/or lacy (delicate, reticular) in pattern, reflecting the underlying chondroid matrix and mineral deposition.[1][2]
  • The extent of calcification varies from subtle to extensive; some lesions are predominantly soft tissue density with only focal calcific foci.[2]
  • Unlike the ring-and-arc calcification pattern typical of conventional cartilaginous tumors, CCMN calcification tends to be more amorphous or granular.[2][6]
• The soft tissue component is of homogeneous soft tissue density on conventional radiographs.[2]

Effects on adjacent structures

• CCMN may scallop adjacent bone (extrinsic pressure remodeling) but does not invade or destroy bone.[2]
• In the TMJ region, the mass may displace or compress the mandibular condyle, glenoid fossa, or adjacent soft tissues.[4]
• No periosteal reaction has been described.[2]
• Tooth displacement or root resorption has not been reported, consistent with the tumor's extraosseous, periarticular location.[4]

Growth pattern and cortical involvement

• Growth is expansile but non-aggressive, with smooth remodeling of adjacent bone rather than cortical destruction.[2]
• All reported cases with radiologic review have appeared indolent and benign on imaging.[2]

Recognized variants and atypical presentations

• A subset of CCMNs in the TMJ region demonstrate morphologic overlap with chondroid tenosynovial giant cell tumor (TGCT), particularly those harboring FN1::TEK fusions; these may show imaging features overlapping with TGCT.[5]
• Rare superficial/cutaneous presentations have been described in acral locations, appearing as small subcutaneous nodules with calcification.[8]

CT characteristics

• On CT, CCMN appears as a well-defined soft tissue mass with variable internal calcification.[2][4]
• Calcifications range from punctate and scattered to dense and confluent, with the characteristic grungy or lacy pattern best appreciated on thin-section CT.[1][2]
• The soft tissue component is isodense to muscle, with no evidence of aggressive features such as cortical destruction, periosteal reaction, or infiltrative margins.[2]
• Adjacent bone may show smooth scalloping without frank erosion.[2]

MRI characteristics

• MRI demonstrates a well-circumscribed, lobulated mass:[3][4]
  • T1-weighted images: Low to intermediate signal intensity
  • T2-weighted images: Heterogeneous signal, with areas of high signal corresponding to chondroid matrix and low-signal foci corresponding to calcification[4]
  • Post-contrast: Variable, often heterogeneous enhancement[4]
• Signal drop-out on gradient-echo or susceptibility-weighted sequences corresponds to calcified foci.[4]
• MRI is particularly useful for delineating the relationship of TMJ-region CCMNs to the joint capsule, mandibular condyle, and surrounding soft tissues.[4]

Chondroid matrix–producing tumors with calcification in the TMJ region and distal extremities share overlapping imaging features with CCMN. The key diagnostic challenge is distinguishing this benign entity from malignant chondroid neoplasms, particularly chondrosarcoma, to avoid unnecessarily aggressive treatment.[2]

The highest-risk diagnostic pitfall is misdiagnosis as chondrosarcoma, which may lead to radical resection. When a well-circumscribed, calcified chondroid soft tissue mass is encountered in the TMJ region or distal extremity of a middle-aged adult, CCMN should be considered and molecular testing for FN1 rearrangement pursued to confirm the diagnosis before definitive surgical planning.[2][3]

Diagnostic microscopic features

• Multinodular/lobular architecture with a prominent chondroid to cartilaginous matrix.[1][2]
• Tumor cells are polygonal to stellate with eccentric nuclei and bland cytologic features.[1][2]
• Increased cellularity toward the periphery of the nodules, with variable spindled/fibroblastic forms in perinodular septa.[2]
• Grungy and/or lacy calcifications are present in the majority of cases, representing the morphologic hallmark.[1][2]
• Osteoclast-like giant cells are present in a subset of cases.[1][2]

Morphologic variants

• A subset of TMJ-region CCMNs shows features overlapping with chondroid tenosynovial giant cell tumor, including giant cell–rich areas and chondroid metaplasia; these cases frequently harbor FN1::TEK fusions.[5]
• Some cases resemble tophaceous pseudogout with calcium pyrophosphate dihydrate deposition.[1][5]
• Others overlap with the chondroblastoma-like variant of soft tissue chondroma.[1][6]

Molecular findings

• FN1 gene fusions are detected in approximately 76% of cases:[5]
  • FN1::FGFR2 is the most common fusion (~40–50% of fusion-positive cases)[1][4][5]
  • Other partners include FGFR1, TEK, MERTK, NTRK1, FGFR3, and PLAG1[1][5][8]
• A minority harbor PDGFRA::USP8 fusions, particularly those with TGCT-like morphology.[5]
• A subset of morphologically typical CCMNs lack detectable FN1 rearrangements by FISH or NGS, suggesting additional undiscovered genetic drivers.[2][8]
• Unsupervised transcriptomic and methylome clustering confirms CCMN as a molecularly distinct entity separate from conventional soft tissue chondroma and TGCT.[5]

Radiologic-pathologic correlation

• The grungy/lacy calcification pattern visible on imaging directly corresponds to the characteristic mineralized chondroid matrix seen histologically.[1][2]
• The well-circumscribed, lobulated imaging appearance reflects the multinodular histologic architecture.[2]

Immunohistochemistry

• Immunohistochemistry is of limited diagnostic utility; no specific immunophenotype has been established.[7]
• S100 protein may be positive in chondroid areas but is nonspecific.[2]
• Molecular confirmation via FISH or RNA sequencing for FN1 rearrangement is the most reliable ancillary diagnostic tool.[1][5]

Workup and referral

• When a well-circumscribed, calcified chondroid soft tissue mass is identified in the TMJ region or distal extremity, incisional or excisional biopsy is indicated to establish the diagnosis and exclude chondrosarcoma.[2][3]
• Molecular testing for FN1 rearrangement (FISH or RNA sequencing) should be pursued when histologic features are suggestive, particularly to avoid misdiagnosis as a malignant chondroid neoplasm.[1][2][3]

Definitive treatment

• Complete surgical excision is the treatment of choice and is curative in the vast majority of cases.[2][3][4]
• Conservative, margin-negative excision is sufficient; radical resection is not warranted given the benign nature of the tumor.[2][4]

Recurrence and outcomes

• Local recurrence is rare and has been reported only after incomplete excision (2 recurrences among the first ~50 documented cases).[4]
• In the largest series with follow-up (15 of 33 patients), all patients remained disease-free except one who recurred after incomplete excision at the wrist.[8]
• No metastasis or malignant transformation has been reported.[3][4]
• Long-term prognosis is excellent.[3][4]

Surveillance

• Routine long-term surveillance is not well established given the rarity of the entity and its benign behavior.
• Clinical and imaging follow-up may be considered after incomplete excision to monitor for local recurrence.[4]