Pathology: proliferative fasciitis and proliferative myositis

Lobulated; hypocellular; spindle-stellate cells with loose fascicular pattern  

Pale amphophilic cytoplasm

Ovoid nuclei with minimal atypia; inconspicuous mitotic activity

Clusters of epithelioid cells with abundant amphophilic cytoplasm; eccentric nuclei with occasional bi-nucleation

Myxoid stroma; prominent thin-walled vessels 

IHC: smooth muscle actin

Lobulated; hypocellular; spindle-stellate cells with loose storiform-fascicular pattern  

Pale amphophilic cytoplasm

Ovoid nuclei with minimal atypia; inconspicuous mitotic activity

Clusters of epithelioid cells with abundant amphophilic cytoplasm; eccentric nuclei with occasional bi-nucleation

Collagenous stroma with myxoid degeneration

Lobulated; hypocellular; spindle-stellate cells with loose storiform-fascicular pattern  

Ovoid nuclei with minimal atypia; inconspicuous mitotic activity

Clusters of epithelioid cells with abundant amphophilic cytoplasm; eccentric nuclei with occasional bi-nucleation

Collagenous stroma with myxoid degeneration; rare multinucleated giant cells