Fibrous Hamartoma of Infancy

Definition

Triphasic soft tissue mass (fibrous, adipose, primitive mesenchymal) presenting in infants

Most cases under age 4
- Congenital to 19 years
Superficial soft tissue lesion
- Rarely attached to muscle or fascia
Poorly circumscribed
Triphasic lesion
- Spindle cell fibrous trabeculae
  - Variably cellular
- Disorganized mature fat
- Islands of immature mesenchymal cells
  - Small round to spindled cells
  - Cytologically bland
  - Scant cytoplasm, small blue cell pattern
  - May be myxoid
  - Trabeculae of immature mesenchymal cells may occasionally infiltrate fat
Mitotic figures rare in all components
Scattered lymphocytes may be present
Overlying skin may show eccrine changes
- Hyperplasia
- Duct dilation
- Intralumenal papillae
- Squamous metaplasia of ducts

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

Original posting : November 20, 2007
Last Update: March 26, 2014