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
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
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.