Lipoblastoma / Lipoblastomatosis

Definition

Lipoblastoma is a solitary, circumscribed subcutaneous tumor
Lipoblastomatosis is a diffuse infiltrative tumor, usually deep
Very rarely presents over age 20 years
- Usually presents under age 3
Lobular pattern
- Separated by connective tissue septa
- Septa rarely predominate
Immature fat cells admixed with mature fat
- Variable appearances of immature cells
  - Small stellate or round immature mesenchymal cells, without fat vacuoles
  - Prominent single vacuole - signet ring
  - Multiple vacuoles resembling brown fat
- Variable ratios of cell types
  - Maturity may vary between and within cases
  - May appear to mature on subsequent biopsies
  - Occasionally predominantly mature fat, especially in recurrences
  - Mature fat tends to predominate in center of lobules
- Mitotic figures rare, none atypical
Richly vascular myxoid matrix
- More prominent in immature areas
- Plexiform vascular pattern if myxoid matrix is abundant
Occasional features
- Hibernoma-like component with granular eosinophilic cytoplasm
- Entrapped muscle fibers
  - Usually atrophic
- Extramedullary hematopoeisis
Recognition of 18q11-13 abnormalities may expand the clinical and morpohologic spectrum of lipoblastoma / lipoblastomatosis
- Lipoma-like lesions composed virtually entirely of mature adipose tissue
- Atypical lipoma-like lesions with focal atypia
- Hibernoma-like lesions with granular eosinophilic cytoplasm
- Histologically typical lesions in slightly older patients
  - Reported in 23-24 year olds

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