collagenous fibroma; desmoplastic fibroblastoma

Epidemiology

mostly adults, male predominance

Microscopic pathology

• most have infiltrative margins
• spindle or stellate fibroblasts, sparsely distributed in extensive hyalinized/focally myxoid matrix with few blood vessels
• nuclei ovoid, small nucleoli
• mitoses rare or absent
• no necrosis or cytologic atypia

Immunophenotype

• actin focally +
• keratin rare +

Clinical manifestations

• painless, slow growing subcutaneous mass
• wide anatomical distribution, predilection for shoulder & upper limb, often centered around fascial or aponeurotic tissue

Differential diagnosis

• nodular fasciitis
• fibroma of tendon sheath

More general terms

• benign fibroblastic/myofibroblastic neoplasm