Intramuscular Myxoma
Khin Thway, BSc, MBBS, FRCPath
Key Facts
Terminology
Benign soft tissue tumor composed of bland spindle to stellate fibroblasts within abundant extracellular myxoid matrix
Clinical Issues
Middle-aged adults
Female predilection
Site: Large muscles, such as thigh or shoulder
Macroscopic Features
Largely circumscribed, gelatinous mass
May show skeletal muscle infiltration
Microscopic Pathology
Hypocellular and hypovascular
Spindle and stellate cells
Patternless arrays
Mitoses, atypia, and necrosis absent
Cellular variant also exists: Cellular myxoma
 Gross image shows an intramuscular myxoma. This is a circumscribed and lobulated tumor with a white or glistening cut surface. Note the smooth interface with adjacent skeletal muscle. |
 In this intramuscular myxoma, the lesion abuts skeletal muscle  . The lesion is sparsely cellular; the constituent cells are small and bland and arranged in patternless distributions within the myxoid stroma. |
TERMINOLOGY
Definitions
Benign soft tissue tumor composed of bland fibroblasts embedded in abundant extracellular myxoid stroma
Can sometimes be cellular
Cellular or hypercellular intramuscular myxoma
CLINICAL ISSUES
Epidemiology
Age
Middle-aged adults
Gender
Female predilection
Site
Usually large muscles
Thigh
Buttock
Shoulder
Arm
Presentation
