Pathology: myofibroma / Myopericytoma

Myopericytoma

  • Circumscribed; fascicles-whorls of spindle-stellate cells

  • Plump eosinophilic cytoplasm in cells concentrically arranged around vessels; intervening cells have scant cytoplasm and long tapering processes

  • Monomorphic ovoid nuclei; inconspicuous mitotic activity

  • Ectatic medium-sized vessels with variable mural thickness lined by plump vacuolated endothelial cells

  • Intervening stroma is myxoid with occasional mast cells

  • IHC: H-caldesmon

Cellular myofibroma

  • Circumscribed; cellular spindle cell fascicles

  • Pale amphophilic cytoplasm

  • Ovoid nuclei with vesicular chromatin and small nucleoli; rare mitotic activity

  • Prominent dystrophic calcification

  • IHC: smooth muscle actin, desmin, H-caldesmon

  • RNA-seq: SRF::C3orf62 gene fusion

  • PMID: 28248815

Cellular myofibroma

  • Circumscribed; cellular spindle cell fascicles

  • Pale amphophilic cytoplasm

  • Ovoid nuclei with vesicular chromatin and small nucleoli; occasional mitotic activity

  • IHC: smooth muscle actin

  • RNA-seq: SRF::RELA gene fusion

  • PMID: 28248815

Cellular myofibroma

  • Circumscribed; cellular spindle cell fascicles

  • Pale eosinophilic cytoplasm

  • Ovoid nuclei with small nucleoli; rare mitotic activity

  • Delicate curvilinear vasculature

  • RNA-seq: SRF::YAP1 gene fusion*

* To date unreported in the literature

Cellular myofibroma

  • Spindle cell fascicles

  • Pale eosinophilic cytoplasm

  • Ovoid nuclei with occasional inclusions; inconspicuous mitotic activity

  • Occasional collagenous bands

  • RNA-seq: SRF::RELA gene fusion