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Benign cellular myxoma

Summary

Benign cellular myxoma, or cellular myxoma of soft tissue, is a benign myxoid lesion that is histologically partway between intramuscular myxoma and low-grade myxofibrosarcoma. This lesion may also be called intramuscular myxoma.

Adults, with a wide age range - 25 to 83
A mass in the extremities
No abnormality on xray
Marginal excision is curative.
Complete Information on this Tumor
Introduction and Definition: 

This solitary benign lesion occurs in the large muscles of the extremities in adults. It is usually found in the thigh, shoulder, upper arm, hip and buttocks.

Incidence and Demographics: 
Adults 25 to 85. Slighly more likely in females. Mean age around 50.
Symptoms and Presentation: 

A palpable mass with local pain, or a slowly growing painless mass.

X-Ray Appearance and Advanced Imaging Findings: 
No xray findings.
Laboratory Findings: 
None
Differential Diagnosis: 
Soft tissue sarcoma, low-grade myxofibrosarcoma, low-grade fibromyxoid sarcoma, and myxoid liposarcoma, myxoid neurofibroma, myxoid malignant peripheral nerve sheath tumor.
Histopathology findings: 
Grossly tan to tan-yellow. The cut surface has a wet, gelatinous, lobulated appearance. Micro: See the five pathology images shown. 1st picture: Low power showing infiltration of skeletal muscle at the right side by a neoplasm with an extensive myxoid matrix and variable cellularity. 2nd picture: High power showing same as above. The lesions typically are grossly circumscribed but microscopically infiltrative. 3rd: Myxoid tumor with cytologically bland small stellate and spindle cells. There is no atypia, mitoses or necrosis. Small vessels may be seen but are not numerous. 4th: Higher power showing same as 3rd 5th: Less cellular or acellular areas of myxoid matrix may be present and have a microcystic appearance. This appearance by itself would be typical of an intramuscular myxoma; however, finding more the above more cellular myxoid matrix in at least 20% of the tumor makes this a cellular myxoma.
Treatment Options for this Tumor: 
Marginal excision is curative - a more aggressive excision is not needed.
Preferred Margin for this Tumor: 
Marginal
Outcomes of Treatment and Prognosis: 
Excellent prognosis, with low rate of recurrence.
Suggested Reading and Reference: 
Histopathology. 2001 Sep;39(3):287-97. Cellular myxoma of soft tissue: a clinicopathological study of 38 cases confirming indolent clinical behaviour. van Roggen JF, McMenamin ME, Fletcher CD.