Discussion

Lipoblastoma is a rare, benign, rapidly growing tumor of embryonal white fat that resembles fetal adipose tissue and occurs predominantly in infants and young children, with approximately 75–90% of cases diagnosed before age 3 and a clear male predominance; adult cases are exceptional. It most often presents as a painless mass in the subcutaneous tissues of the trunk or extremities. However, the head and neck, mediastinum, retroperitoneum, mesentery, visceral organs, and spinal canal may also be involved. Two forms are recognized: circumscribed lipoblastoma, which is superficial, localized, well-defined, and generally amenable to complete excision, and diffuse lipoblastomatosis, which infiltrates deeper soft tissue and muscle, is more difficult to remove completely, and carries a higher risk of recurrence. Large or strategically located lesions can compress adjacent structures, causing airway compromise, neurologic deficits, or functional impairment.

Grossly, lipoblastoma is typically a well-circumscribed, soft, lobulated, pale yellow-tan mass measuring approximately 2–6 cm, although rare tumors exceed 10 cm or weigh up to 1 kg; the cut surface may contain white-gray fibrous septa, myxoid or gelatinous nodules, cystic spaces, and occasional cartilaginous metaplasia. Histologically, the tumor forms irregular lobules containing adipocytic cells at different stages of maturation, including primitive mesenchymal cells, lipoblasts, and mature adipocytes. Primitive mesenchymal cells can be stellate or spindle-shaped, whereas lipoblasts can be multivacuolated or small signet ring-like. Within each lobule, immature myxoid cells commonly lie at the periphery, while mature fat is concentrated toward the center. Variably thick fibrous septa, stromal mucin, delicate plexiform capillaries, and occasional brown fat-like cells may be present. Prominent myxoid areas may mimic myxoid liposarcoma; however, nuclear atypia and mitotic activity are absent. Diffuse lipoblastoma (lipoblastomatosis) shows infiltrative growth, less distinct lobulation, and entrapped skeletal muscle. Recurrent or longstanding lesions may mature into tissue resembling lipoma or fibrolipoma. Immunohistochemistry is usually unnecessary, although spindle cells may express desmin. The characteristic molecular alteration is a PLAG1 rearrangement at 8q11–13.

References

1. Lindburg MR. Lipoblastoma. In: Diagnostic Pathology: Soft Tissue Tumors, 4th ed.: Elsevier; 2023.

2. Lazar AJ, Creytens D, Davis JL, Black JO. Lipoblastoma and lipoblastomatosis. In: WHO Classification of Tumours Editorial Board. Soft Tissue and Bone Tumours. Lyon (France): International Agency for Research on Cancer; 2026. (WHO classification of tumours series, 6th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/87.

3. Folpe AL and Nielsen GP. Enzinger and Weiss's Soft Tissue Tumors, 8th ed.: Elsevier; 2025.

4. Abdul-Ghafar J, Haidari M, Ud Din N. Lipoblastoma / lipoblastomatosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueadiposelipoblastoma.html. Accessed October 10th, 2026.