Stanford School of Medicine

Surgical Pathology Criteria

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Juxta-articular Myxoma


  • Generally hypocellular, hypovascular, bland pure myxoid lesion arising adjacent to a large joint

Diagnostic Criteria

  • Adjacent to a large joint
  • Grossly circumscribed, microscopically infiltrative
  • Generally hypocellular and hypovascular
    • Abundant myxoid matrix
    • Areas of increased cellularity and vascularity may be seen
  • Cytologically bland
    • Small stellate or spindled cells
    • No pleomorphism
    • No atypia, mitoses or necrosis
  • May have focal inflammation or hemorrhage

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: February 3, 2007

Supplemental studies


Vimentin Positive
Smooth muscle actin Rare
Desmin Negative
S100 Negative
CD68 Muciphages positive


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


  • Age 16-83 years
  • 0.6-12 cm, most under 5 cm
  • Associated with large joint
    • Usually knee
  • Frequently associated with torn meniscus or osteoarthritis
  • 34% recurrence rate but not destructive

Grading / Staging / Report

Grading and staging not applicable

The surgical pathology report should contain or address the following:

  • Location
  • Type of resection or biopsy
  • Histologic diagnosis
  • Managerial category Ib (Recurrences do occur but are not destructive; never metastasizes)
  • Size
  • Depth (dermis, subcutis, below fascia, body cavity)
  • Margins
    • Involved
    • Not involved
  • Results of supplementary studies if performed
  • Relationship to other specimens from the same patient


Soft tissue lesions that frequently are prominently myxoid


  • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
  • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
  • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
  • Meis JM, Enzinger FM. Juxta-articular myxoma: a clinical and pathologic study of 65 cases. Hum Pathol 1992 Jun;23(6):639-46
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