Surgical Pathology Criteria

Juxta-articular Myxoma

Differential Diagnosis

Myxoid Neurofibroma Juxta-articular Myxoma
May involve nerve No nerve involvement
S100 positive S100 negative


Juxta-articular Myxoma Intramuscular Myxoma
Adjacent to large joint Intramuscular
May be more cellular Extremely paucicellular
Lacks Gs(alpha) mutation Gs(alpha) mutation frequent


Myxoid Liposarcoma Juxta-articular Myxoma
Lipoblasts present, usually signet ring type No lipoblasts
Arborizing vascular pattern Hypovascular


Low Grade Fibromyxoid Sarcoma Juxta-articular Myxoma
Alternating fibrous and myxoid patterns Uniform myxoid pattern
Swirling, whorled pattern No swirling, whorled pattern


Myxofibrosarcoma Intramuscular Myxoma and Juxta-articular Myxoma
Pleomorphism present Uniformly small bland cells
More cellular Extremely paucicellular
Mitotic figures may be present Mitotic figures practically never present
Arching vessels Markedly hypovascular


Cellular Myxoma Juxta-articular Myxoma
Bland and cellular but lacks classical hypocellular areas Hypocellular areas present
Arching vessels Lacks arching vascular pattern


Juxta-articular Myxoma Nodular Fasciitis
No grouping of cells Undulating bundles of cells
No tissue culture appearance Tissue culture appearance with tears and spaces in tissue
Rare mitotic figures Frequent mitotic figures

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