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intramuscular myxoma

Tuesday 3 February 2004

Intramuscular myxoma is a benign soft-tissue tumor that presents as a deeply seated mass confined to skeletal muscle.

Digital case

- JRC:2276 : Soft tissueas (thigh). Intramuscular myxoma. Special stains (not included): CD34: + / desmin, HHF35, SMActin, F13a, CD68: negative. 51 y/o female.

Definition

Intramuscular myxoma (cellular myxoma) have sometimes been known as low-grade myxoid neoplasm with recurrent potential.

They in fact have only a very low rate of local non-destructive recurrence and which should not be confused with myxofibrosarcoma.

Microscopy

- hypocellular, hypovascular regions
- cytologically bland stellate and bipolar fibroblasts separated by abundant extracellular myxoid matrix
- areas of increased cellularity and vascularity that can lead to a mistaken diagnosis of sarcoma

  • The hypercellular regions are not associated with cytologic atypia of the constituent cells, mitotic activity, or necrosis. (9777984)

Immunochemistry

- absence of MUC4 expression. (23685711)

Cytogenetics

- hyperdiploidy
- trisomy 18

Differential diagnosis

- myxofibrosarcoma
- low-grade fibromyxoid sarcoma (LGFMS)
- myxoid liposarcoma

Prognosis

- Surgical excision is virtually always curative. - Recurrence, even after incomplete resection, is exceptional.

References

- Intramuscular myxoma of the buttock mimicking low-grade fibromyxoid sarcoma: diagnostic usefulness of MUC4 expression. Yamashita H, Endo K, Takeda C, Teshima R, Osaki M, Yoshida H. Skeletal Radiol. 2013 Oct;42(10):1475-9. doi : 10.1007/s00256-013-1641-4 PMID: 23685711

- The evolving classification of soft tissue tumours: an update based on the new WHO classification. Fletcher CD. Histopathology. 2006 Jan;48(1):3-12. PMID: 16359532

- Nielsen GP, O’Connell JX, Rosenberg AE. Intramuscular myxoma: a clinicopathologic study of 51 cases with emphasis on hypercellular and hypervascular variants. Am J Surg Pathol. 1998 Oct;22(10):1222-7.
PMID: 9777984

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