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Lipofibromatosis

Definition

  • Pediatric neoplasm composed of fat with a septal fibroblastic component

Diagnostic Criteria

  • Age range birth to 12 years
  • Predominantly fatty tissue
    • Mature fat
    • Occasional small collections of univacuolated cells
      • At interface of fibroblastic and fat components
      • Vacuoles do not indent nucleus as in lipoblasts
  • Fascicles of fibroblastic cells
    • Predominantly in septa of fat
  • Collagen generally scant to moderate
    • Occasionally myxoid
    • Lack primitive myxoid mesenchymal nodules
  • No significant atypia or pleomorphism
    • Mitotic figures infrequent
  • Poorly defined margin
    • Frequently involves and entraps vessels, nerves, muscle, skin adnexa
  • Scattered pigmented spindled / dendritic cells in 2/45 cases

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

Original posting : July 29, 2007

Supplemental studies

Immunohistology

Spindled fibroblastic cells
CD99 10/12
CD34 12/13
Smooth muscle actin 10/12
bcl2 7/12
S100 5/14
Muscle specific actin 3/13
EMA 2/12
Desmin neg
Keratin neg
Beta-catenin neg

 

Pigmented spindle cells (rare)
Tyrosinase 2/2
MelanA 2/2
HMB45 1/2
S100 1/2

Differential Diagnosis

Hemosiderotic Fibrohistiocytic Lipomatous Lesion Lipofibromatosis
Circumscribed Poorly circumscribed
Prominent hemosiderin Lacks hemosiderin
Includes histiocytes and other inflammatory cells Histiocytes and inflammation not integral to lesion
Occasional floret cells Lacks floret cells

Neural Fibrolipoma (Fibrolipomatous Hamartoma of Nerve) Lipofibromatosis
Fat with fibrous component Fat with cellular fibroblastic septa
Centered on and surrounds a major nerve with epineurial and perineurial thickening Soft tissue mass, may surround nerve focally
Frequently associated with macrodactyly Not associated with macrodactyly

Infantile Fibromatosis Lipofibromatosis
Solid, sheet-like pattern Septal fibroblastic pattern
Overrun, effaced fat Fat is integral part of lesion
Usually head, neck, shoulder, thigh Usually distal extremities
Lipofibromatosis may represent part of the spectrum of infantile fibromatosis

Fibrous Hamartoma of Infancy Lipofibromatosis
Rarely if ever in hands or feet Frequently hand or feet
Hyalinized, "wire-like" collagen Collagen not prominent
Whorled, myxoid nodules of immature cells Myxoid areas lack nodular pattern

Lipoblastoma / Lipoblastomatosis Lipofibromatosis
Septa infrequently cellular Prominently cellular septa
Usually immature fat mixed with mature Mature fat
Fat cells may have multiple vacuoles Single fat vacuoles

Calcifying Aponeurotic Fibroma Lipofibromatosis
Lacks fatty component Fat is integral to lesion
Cellular nodules of epithelioid cells with palisading Septal fibroblastic pattern
Chondroid differentiation and calcification common Lacks chondroid differentiation and calcification
Both frequently involve hands or feet

Clinical

  • Age range birth to 12 years
  • Site
    • Predominantly extremities (80%)
  • Behavior
    • Recurrence / persistence in 72% of cases
    • No metastases

Lists

Lipogenic tumors

Bibliography

  • Fetsch JF, Miettinen M, Laskin WB, Michal M, Enzinger FM. A clinicopathologic study of 45 pediatric soft tissue tumors with an admixture of adipose tissue and fibroblastic elements, and a proposal for classification as lipofibromatosis. Am J Surg Pathol. 2000 Nov;24(11):1491-500.

     

     

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