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

Differential Diagnosis

• Hemosiderotic fibrolipomatous lesion
• Neural Fibrolipoma
• Juvenile fibromatosis
• Fibrous hamartoma of infancy
• Lipoblastoma / lipoblastomatosis
• Calcifying aponeurotic fibroma

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

• Angiomyolipoma
• Hemosiderotic Fibrohistiocytic Lipomatous Lesion
• Hibernoma
• Lipofibromatosis
• Lipoma
• Lipomatosis
• Lipoblastoma / lipoblastomatosis
• Pleomorphic lipoma
• Spindle cell lipoma
• Atypical lipomatous tumor
• Liposarcoma
  • Dedifferentiated
  • Myxoid
  • Pleomorphic
  • Unclassified

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.