Age / Sex : 61 / F

Chief complaint: Pain and swelling, left thigh
What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

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Courtesy: Sheen Woo Lee, Gachon University

Proliferative myositis

Discussion

Findings: Enhancing infiltrative mass-like lesion, hyperintense on T2WI, isointense on T1WI.

Relatively preserved muscle fibers inside the lesion.

Differential Diagnosis: 1) proliferative myositis, 2) lymphoma, 3) sarcoidosis.

Diagnosis: US-guided biopsy ; consistent with proliferative myositis

Discussion:

Rare benign inflammatory myopathy characterized by infiltration with basophilic giant cells and proliferative fibroblasts
Adults (mean age, 50 years)

Rapidly enlarging solitary soft tissue mass that is often firm and painful

Cause: Unknown. History of recent local trauma is noted in some cases

Plain radiograph

Nonspecific, well or ill-defined soft-tissue masses with or without calcification

Soft-tissue masses of PM may rarely extend to adjacent osseous structures

CT

Mass that is hypo- or iso attenuating relative to the skeletal muscle, and contrast enhancement may be homogeneous, heterogeneous, or absent

MR

Hypo- or isointense T1 SI compared with that of muscle and homogeneous enhancement,

hyperintense on T2WI

No signal intensity changes related to blood or calcification on gradient echo image

Preserved the muscle fibers without disruption

Treatment :

Recommend no specific treatment, since it may disappear spontaneously

Excision may be preferred to establish a diagnosis and for cosmetic reasons

Recurrence extremely rare

References:

Proliferative Myositis, Radiology 2007; 244:613– 616

Proliferative myositis in a child, Skeletal Radiol (1999) 28:703–709

Proliferative myositis: a rare pseudosarcoma of the chest wall. Ann Thorac Surg 2002;73:1296–1298.