Intramuscular Myxoma

Definition

Generally hypocellular, hypovascular, bland pure myxoid lesion arising in skeletal muscle

Markedly hypocellular and hypovascular
- Abundant myxoid matrix
- Areas of increased cellularity and vascularity may be seen
  - Must not involve >20% of a given tumor
    - If >20%, designate as cellular myxoma
  - No atypia, mitoses or necrosis even in cellular areas
  - No difference in clinical behavior
Involves skeletal muscle
Grossly circumscribed, microscopically infiltrative
Cytologically bland
- Small stellate or spindled cells
- No pleomorphism
- No atypia, mitoses or necrosis
- May have microcystic appearing acellular areas
Muciphages may be present
No lipoblasts

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