Hemosiderotic Fibrohistiocytic Lipomatous Lesion

Definition

Hemosiderotic Fibrolipomatous Tumor
Proposed to be equivalent to early lesion pattern of pleomorphic hyalinizing angiectatic tumor

Variably circumscribed mass of mature fat
- No adipocyte atypia
  - Occasional cases with focal fat necrosis
- Cellular fibrous septa separate fat into lobules
Bland spindle cells in septa and infiltrating fat
- May form cellular nodules
- Infiltration of fat may produce "honeycomb" pattern
- No significant atypia
  - Inconspicuous nucleoli
  - Mitotic figures <1/10 hpf
Abundant hemosiderin
- Primarily in histiocytes in spindled areas
- Some hemosiderin in spindled cells
Nearly all cases in distal extremities
Osteoclast-like multinucleated giant cells in most cases
- Occasional cases with floret cells
Stroma may be focally myxoid
- Rare cases with psammoma bodies or metaplastic ossification
Vessels occasionally have fibrin thrombi and mural hyalinization
Scattered lymphocytes, plasma cells and mast cells
Proposed to be equivalent to early lesion pattern of pleomorphic hyalinizing angiectatic tumor

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