Cellular Myxoma

Definition

• Cellular, bland pure myxoid lesion arising in deep soft tissues

Alternate / historical names

• Low grade myxoid neoplasm with recurrent potential
• Myxoid tumor with recurring potential

Diagnostic Criteria

• Extensive myxoid matrix
  • Areas of collagenous stroma may be present
• Moderately cellular
  • Intermediate in cellularity between intramuscular myxoma and low grade myxofibrosarcoma
  • Cellular areas comprise at least 20% of tumor
    • We consider lesions with <20% cellular areas to be usual intramuscular myxomas
  • Areas of classic markedly hypocellular myxoma are nearly always present
• May have moderate vascularity
  • Vessels may have arching, curvilinear pattern
  • Primarily capillaries
  • Occasional larger vessels may be seen, probably entrapped
• Cytologically bland
  • Small stellate or spindled cells
  • Mildly hyperchromatic but not pleomorphic
  • No atypia, mitoses or necrosis
  • May have microcystic appearing acellular areas
• Involves deep soft tissue
  • 50% have intramuscular component
  • Majority in extremities or limb girdles
• Grossly circumscribed, microscopically infiltrative
• Muciphages may be present
  • No giant cells
  • No lipoblasts

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

Original posting:: September 25, 2007

Supplemental studies

Immunohistology

Differential Diagnosis

• Aggressive angiomyxoma
• Myxoid neurofibroma
• Low grade fibromyxoid sarcoma
• Myxoid liposarcoma
• Low grade myxofibrosarcoma
• Intramuscular myxoma
• Juxta-articular myxoma

Cellular Myxoma	Aggressive Angiomyxoma
Frequently on extremities	Perineal or pelvic
Medium to large vessels infrequent	Prominent medium to large vessels

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

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

Myxoid Liposarcoma	Cellular Myxoma
Arborizing vascular pattern	Capillaries may be arching but lack well developed arborizing, chickenwire pattern
Lipoblasts present, usually signet ring type	No lipoblasts

Myxofibrosarcoma	Cellular Myxoma
Pleomorphism present	Uniformly small bland cells
Mitotic figures may be present	Mitotic figures rare
May have perivascular increase in cellularity	No perivascular increase in cellularity

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	Cellular Myxoma
Adjacent to large joint	Not adjacent to large joint

Histologically these may be identical; they both have a potential to recur

Clinical

• Age 25-83 years
• Size reported up to 14 cm
• Most in proximal limbs and adjacent trunk
• Involves deep soft tissue
  • 50% are intramuscular
• 5-10% may recur
  • Recurrences reported in incompletely excised cases
• No metastases

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 Ia (Local excision is almost always curative; metastasis never occurs)
• Extent of tumor cell necrosis
• 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

Lists

Soft tissue lesions that frequently are prominently myxoid

• Aggressive angiomyxoma
• Cellular myxoma
• Intramuscular myxoma
• Juxta-articular myxoma
• Low grade fibromyxoid sarcoma
• Low grade myxofibrosarcoma
• Myxoid chondrosarcoma
• Myxoid liposarcoma
• Myxolipoma
• Ossifying fibromyxoid tumor
• Myxoid nerve sheath tumor
• Superficial acral fibromyxoma
• Superficial angiomyxoma

Bibliography

• 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
• van Roggen JF, McMenamin ME, Fletcher CD. Cellular myxoma of soft tissue: a clinicopathological study of 38 cases confirming indolent clinical behaviour. Histopathology 2001 Sep;39(3):287-97
• Nielsen GP, O'Connell JX, Rosenberg AE. Intramuscular myxoma: a clinicopathologic study of 51 cases with emphasis on hypercellular and hypervascular variants. Am J Surg Pathol 1998 Oct;22(10):1222-7