Surgical Pathology Criteria

Intramuscular Myxoma

Differential Diagnosis

Intramuscular Myxoma Aggressive Angiomyxoma
Frequently on extremities Perineal or pelvic
Hypovascular Prominent medium to large vessels

Myxoid Neurofibroma Intramuscular Myxoma
May involve nerve No nerve involvement
S100 positive S100 negative

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

Myxoid Liposarcoma Intramuscular Myxoma
Arborizing vascular pattern Hypovascular
Lipoblasts present, usually signet ring type No lipoblasts
More cellular Extremely paucicellular

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 Intramuscular Myxoma
Moderate cellularity must comprise at least 20% of lesion Markedly hypocellular
Arching vessels may be present Markedly hypovascular
May have areas of collagenous stroma Uniformly myxoid stroma

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

Intramuscular Myxoma Nodular Fasciitis
Very hypocellular Moderately cellular
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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