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

• Spindle cells with fascicular-storiform pattern

• Eosinophilic cytoplasm

• Ovoid nuclei with small nucleoli; inconspicuous mitotic activity

• IHC: desmin, smooth muscle actin, H-caldesmon, keratin (AE1/AE3)

• RNA-seq: SRF::CITED1 gene fusion

• PMID: 33021523

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