Myofibroma, Solitary and Multicentric

Definition

Generally biphasic tumor composed of mature and immature myofibroblastic cells with hemangiopericytoma-like vessels. May be solitary or multicentric

Superficial lesions circumscribed, deep lesions infiltrative
- Both may be microscopically infiltrative
Generally biphasic nodules (see below for exceptions)
- Light staining bundles of mature nyoid cells usually on periphery of nodules
  - Moderate amount of well defined cytoplasm
  - Generally vesicular nuclei
  - Peripheral chronic inflammation may be present
- Dark staining areas of primitive oval to spindle cells usually in center of nodules
  - Scant indistinct cytoplasm

Mitotic figures may be frequent
- No atypical figures
Atypical features are of no clinicall significance
- Intravascular growth frequent
- Primtive spindle cell areas may be very cellular and predominate
  - May approach cellularity of fibrosarcoma but lacks atypia
- Mild pleomorphism may be present
- Central necrosis may be present
  - Rare in infants
Both cell types actin positive
Exceptions to usual pattern
- Occasional domination of either type
- Mature cell type more predominant in lung
- Immature cell type more predominant in bone
- Reversal of zonation occasionally seen in adults
Infantile lesions show common features with infantile hemangiopericytoma
- We consider them to be the same entity
Adult lesions have been proposed as part of a spectrum including glomangiopericytoma and myopericytoma

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting / last update: 8/10/08, 11/23/14