Pathology: nodular fasciitis

Nodular fasciitis

• Circumscribed; spindle cells with fascicular-storiform pattern

• Pale amphophilic cytoplasm

• Ovoid nuclei with minimal atypia and small nucleoli; inconspicuous mitotic activity

• Myxoid-collagenous  stroma; extravasation of erythrocytes

• RNA-seq: MYH9::USP6 gene fusion

Nodular fasciitis

• Spindle cells with fascicular-storiform pattern

• Pale amphophilic cytoplasm

• Ovoid nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Collagenous-myxoid stroma; rare extravasation of erythrocytes

• RNA-seq: MYH9::USP6 gene fusion

Nodular fasciitis

• Circumscribed; spindle cells with fascicular-storiform pattern  

• Pale amphophilic cytoplasm

• Ovoid nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Myxoid stroma with broad bands of collagen; mild chronic inflammation; extravasion of erythrocytes

• IHC: smooth muscle actin

• RNA-seq: MYH9::USP6 gene fusion

Nodular fasciitis

• Circumscribed; spindle cells with fascicular-storiform pattern  

• Pale amphophilic cytoplasm

• Ovoid nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Myxoid stroma with broad bands of collagen; mild chronic inflammation; extravasion of erythrocytes

• IHC: smooth muscle actin

• RNA-seq: COL1A2::USP6 gene fusion

Nodular fasciitis

• Lobulated; spindle cells with storiform pattern  

• Pale amphophilic cytoplasm

• Ovoid nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Mild chronic inflammation; focal myxoid degeneration

• RNA-seq: MYH9::USP6 gene fusion

Nodular fasciitis

• Circumscribed; spindle cells with vague fascicular-storiform pattern  

• Pale amphophilic cytoplasm

• Ovoid elongated nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Broad bands of collagen with focal myxoid degeneration; mild chronic inflammation

• RNA-seq: MYH9::USP6 gene fusion

Nodular fasciitis

• Circumscribed; spindle cells with fascicular-storiform pattern  

• Pale amphophilic cytoplasm

• Ovoid elongated nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Broad bands of collagen with focal myxoid degeneration; mild chronic inflammation

• RNA-seq: MYH9::USP6 gene fusion

Nodular fasciitis

• Spindle cells with storiform pattern  

• Pale amphophilic cytoplasm

• Ovoid nuclei with minimal atypia and small nucleoli; occasional mitotic activity

• Mild chronic inflammation; focal myxoid degeneration; focal extravasation of erythrocytes

• RNA-seq: MYADM::USP6* gene fusion

* To date "MYADM-" is unreported in this context