Lipoblastoma and infantile lipoma.

To The Editor: A 1-year-old male Saudi child was admitted in the pediatric ward with a soft, mobile right axillary mass measuring 3×4 centimeters. No signs of inflammation were seen over the swelling, and no similar swelling was noticed on the child. His blood examination showed lymphocytosis, and the tuberculin test was negative. An excisional biopsy of the axillary mass was performed to rule out lymph node disorder. The specimen, sent to the histopathology lab in 10% buffered formalin, consisted of a fairly circumscribed, whitish yellow, lobulated fatty mass measuring 6×3×1 centimeters. The cut surface of the mass was whitish yellow, homogenous with lobulations (Figure 1). Touch imprint of the mass showed adipocytes and no lymphoid cells. Microscopic examination showed lobules of lipoblasts interspersed between spindle and stellate mesenchymal cells, and suspended in a myxoid strauma with a plexiform vascular pattern (Figure 2).

Figure 1

Whitish yellow, greasy, lobulated appearance of the infantile lipoma.

Figure 2

Lobules of lipoblasts, showing a plexiform vascular pattern.

Lipoblastoma are benign mesenchymal tumor of embryonic white fat, with a postnatal spectrum of differentiation, ranging from prelipoblasts and mature adipocytes. The term infantile lipoma was suggested, as it reflects many of the tumor characteristics, such as early occurrence, an ability to mature into a simple lipoma, and a benign course, as the word blastoma is associated with a more malignant nature.5 Moreover, the microscopic arborising vascular pattern, myxoid strauma, and lipoblasts, in a case of lipoblastoma, resembles myxoid liposarcoma—a malignant tumor. However, liposarcomas rarely if ever occur in infants and children, and lack the lobular organization of lipoblasts seen in lipoblastoma.6 Lipoblastoma also lack giant cells and pleomorphic nuclei.7 Ultrastructurally, cells varying in appearance from primitive mesenchymal cells to typical multivaculated lipoblasts are seen in lipoblastoma,8,9,10 and these cells are very similar to cells in myxoid liposarcoma.11

Cytogenetic studies show that infantile lipoma is associated with rearrangements of 8q and trisomy of chromosome 8.12 In contrast, the cytogenetics of myxoid liposarcoma are characterized by reciprocal translocation of t(12 :16) (q 13:9 11), which results in the rearrangement of the transcription factor gene CHOP, involved in the adipocyte differtiation.13,14,15,17

A pre-operative diagnostic test for lipoblastoma would include fine needle aspiration cytology.15 An intra-operative touch imprint and frozen section can rule out other differential diagnosis. Excision biopsy is the treatment of choice and a recurrence rate of 14% to 25 % are reported from incomplete removal.16