nodular fasciitis (pseudosarcomatous fasciitis)

Epidemiology

• common among soft tissue mass lesions
• all age groups, most often young adults

Pathology

• usually subcutaneous, may be intramuscular
• upper extremities, trunk, head & neck most frequently affected
• intravascular fasciitis - extends into vessel lumen
• cranial fasciitis - involves skull

Microscopic pathology

• plump, uniform fibroblastic/myofibroblastic cells
• may be highly cellular
• sometimes storiform pattern
• typically some loose or tissue culture like pattern
• lacks nuclear hyperchromasia or pleomorphism
• usually little collagen, but may have focal keloid-like collagen bundles
• mitoses may be plentiful, but are not atypical
• extravasated red cells, chronic inflammatory cells and multinucleated osteoclast-like giant cells common
• border of tumor typically infiltrative, at least focally
• occasionally osseous metaplasia seen

Immunophenotype

• SMA, MSA usually positive
• desmin rarely positive
• keratin, S100 negative
• CD68 + osteoclast-like giant cells & occasional spindle cell

Clinical manifestations

• rapidly growing, most cases ~1-2 months prior to surgery
• soreness or tenderness
• almost always < 5 cm, (usually < 2 cm.)
• some report previous trauma at site
• recurrence after excision rare, similar for cranial fasciitis and intravascular fasciitis

More general terms

• benign fibroblastic/myofibroblastic neoplasm