Age / Sex : 48 / F

CASE 1 : F /48

Chief complaint : Palpable mass for 2 months in the proximal upper arm

CASE 2 : F/51

Chief complaint : Palpable mass for 2 years in the left proximal thigh


What is your impression?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Chang Ho Kang, Korea University Anam Hospital

Discussion

Answer:  Intramuscular myxoma

Findings:

Case 1) MR images show a well-circumscribed mass within the left deltoid muscle. Coronal T1-weighted MR image demonstrates a homogeneous, hypointense mass with perilesional fat at the upper pole. Coronal fat-suppressed T2-weighted MR image demonstrates a homogeneously very hyperintense mass with perilesional edema. Coronal contrast-enhanced T1-weighted image shows heterogeneous enhancement. US image shows a well-defined, hypoechoic mass with perilesional fatty cap at the pole of the lesion.

Case 2) MR images show a well-circumscribed mass within the left vastus lateralis muscle. Coronal T1-weighted MR image demonstrates a homogeneous, hypointense mass with perilesional fat rind. Coronal fat-suppressed T2-weighted MR image demonstrates a homogeneously very hyperintense mass with perilesional edema. Coronal fat-suppressed contrast-enhanced T1-weighted image shows peripheral rim enhancement. US image shows a well-defined, heterogeneously hypoechoic mass with perilesional fatty caps.

Differential Diagnosis:

1) Soft tissue sarcoma with myxoid component

2) Neurogenic tumor

3) Proliferative myositis

Discussion:

Intramuscuar myxoma is the most common benign myxoid neoplasm, consisting of abundant myxoid stroma interspersed with benign spindle cells. Intramuscular myxoma is most frequently diagnosed in patients 40–70 years of age. The most common presentation is a slowly growing painless mass. Intramuscular myxomas are typically solitary. When multiple myxomas are present, they are almost always associated with monostotic or polyostotic fibrous dysplasia, known as Mazabraud syndrome. Most musculoskeletal myxomas are intramuscular (82%) in location, occurring most often in the thigh (51%), followed by upper arm (9%), calf (7%), and buttock (7%). On MRI, the lesions are well circumscribed with smooth or slightly lobulated margins, homogeneously hypointense on T1-weighted images, and extremely hyperintense on T2-weighted images. On contrast-enhanced images, lesions show variable heterogeneous, sometimes avid, contrast enhancement due to the presence of abundant vascularity within the myxoid matrix. The presence of a perilesional rind of fat (65%-89%) or perilesional edema on fluid-sensitive sequences (79%-100%) has been described to be highly suggestive of the diagnosis on MRI. Surgical excision with wide margins is the treatment of choice for intramuscular myxomas, with recurrence being rare.

References:

1. JM Petscavage-Thomas, EA Walker, CI Logie, et al. Soft-Tissue Myxomatous Lesions: Review of Salient Imaging Features with Pathologic Comparison. RadioGraphics 2014;34:964-980.


2. LW Bancroft, MJ Kransdorf, DM Manke, et al. Intramuscular Myxoma: Characteristic MR Imaging Features. AJR 2002;178:1255-1259.


3. A Luna, S Martinez, E Bossen. Magnetic Resonance Imaging of Intramuscular Myxoma with Histological Comparison and a Review of the Literature. Skeletal Radiol 2005;34:19-28.


4. JS Wu, MG Hochman. Soft-Tissue Tumors and Tumorlike Lesions: A Systematic Imaging Approach. Radiology 2009;253:297-316.