Calcifying Fibrous Pseudotumor

Definition

Paucicellular collagenous lesion with scattered chronic inflammation and focal calcifications

Paucicelluar
- Bland spindle cells
  - Scant cytoplasm
  - Mitotic figures very rare
- Scattered lymphocytes and plasma cells
  - Plasma cells usually predominate
  - May include germinal centers
  - May include eosinophils, neutrophils and mast cells
Abundant dense hyalinized collagenous stroma
- Haphazard or whorled
Focal small calcifications
- Range from psammomatous to irregular, dystrophic
- Rarely ossifying
Varies from circumscribed to infiltrative
- Not encapsulated
- May be multilobulated
- May entrap nerves, vessels and fat
Calcifying fibrous pseudotumor has been proposed to represent a sclerosing stage of inflammatory myofibroblastic tumor

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

Original posting: March 15, 2008