Intramuscular Myxoma – Overview

Definition:

Intramuscular myxoma is a rare, benign (non-cancerous) soft tissue tumor composed of immature fibroblasts and abundant myxoid (gel-like) stroma. It usually arises within the skeletal muscle and grows slowly.

Epidemiology:

• Incidence: Rare (less than 1 per million)

• Age group: Most common in adults between 40–70 years

• Sex: Slight female predominance

Common Locations:

• Thigh

• Shoulder

• Buttocks

• Arm or calf muscles

Symptoms:

• Painless, slowly enlarging soft tissue mass

• Usually non-tender

• Rarely causes functional impairment

• May go unnoticed for years

Causes and Risk Factors:

• Mostly sporadic, with no known cause

• May be associated with Mazabraud’s syndrome (a rare condition combining intramuscular myxomas and fibrous dysplasia of bone)

Diagnosis:

1. Imaging:

• MRI: Preferred method

  • Well-defined, homogeneous, hypointense on T1, hyperintense on T2

  • May show mild enhancement with contrast

• Ultrasound: Shows a hypoechoic, well-demarcated mass

2. Biopsy:

• Histopathology confirms diagnosis:

  • Spindle-shaped cells

  • Scant cytoplasm

  • Abundant myxoid matrix

  • Low cellularity

  • No atypia or mitosis

Differential Diagnosis:

• Myxoid liposarcoma

• Low-grade fibromyxoid sarcoma

• Nodular fasciitis

• Ganglion cyst

• Neurogenic tumor

Treatment:

• Surgical excision is the treatment of choice

  • Complete removal with clear margins

  • Recurrence is rare if fully excised

Prognosis:

• Excellent

• No risk of malignancy

• Very low recurrence rate after complete resection

Conclusion:

Intramuscular myxoma is a benign tumor of muscle tissue that presents as a painless mass, typically in middle-aged adults. While rare, it is important to distinguish it from malignant tumors using imaging and biopsy, with surgical excision being curative in most cases.