summary Intramuscular Myxomas are benign soft tissue tumors that present as slow-growing deeply seated masses confined within the skeletal muscle. The condition is typically seen in patients between 40 and 60 years of age who present with a slow-growing mass that may or may not be painful. Diagnosis is made with MRI studies showing a homogenous mass with an intramuscular location. Treatment is observation for asymptomatic lesions. Marginal surgical excision is indicated for symptomatic lesions that do not resolve with nonoperative management. Epidemiology Demographics occur in 40 to 60 year olds slight female predilection Associated conditions commonly located in the thigh, shoulder, buttock, or upper arm Etiology Mechanism likely develop from premature mesenchymal stem cells which differentiate into benign fibroblasts which loose their capacity to secrete collagen Associated conditions Mazabraud's syndrome a syndrome characterized by multiple intramuscular myxomas associated with monostotic or polyostotic fibrous dysplasia myxoid liposarcomas important to differentiate from a myxoid liposarcomas, which occurs in an intermuscular location Presentation Symptoms slowly growing mass may or may not be painful pain in soft tissue sarcomas is often based on compression of surrounding tissues like vessels or nerves Imaging MRI homogeneous appearance bright T2 signal dark T1 signal intramuscular location intramuscular location of myxomas is important to differentiate from myxoid liposarcoma, which occurs in an intermuscular location Studies Histology characterized by bland and hypo-cellular myxoid stroma no cellular atypia low nuclear to cytoplasmic ratio no atypical mitosis Treatment Nonoperative observation indications for asymptomatic lesions Operative marginal surgical excision indications symptomatic benign low-grade tumors neoadjuvant chemo-radiotherapy is not needed local recurrence and metastasis uncommon Prognosis Local recurrence and metastasis uncommon