intramuscular myxoma

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.

Images

 https://twitter.com/TexPathol/status/1146751114135691268

Digital case

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

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)

• differential diagnosis with MUC4+ low-grade fibromyxoid sarcoma (LGFMS)

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.

See also

 myxoid tumors

• myxomas / myxoma

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