Chondroid Lipoma : Morphology

Comments:
Gross Morphology: Chondroid lipoma is well-circumscribed and encapsulated. The gross appearance is yellow, white, or pink-tan. The size ranges from 1 to 11 cm. The tumor is located in the subcutaneous tissues, superficial fascia, or entirely within skeletal muscle.

Microscopic Features: It consists of nests and clusters of round tumor cells arranged in a lobular pattern in a background of myxochondroid or hyalinized fibrous stroma. Some of the cells have lipid vacuoles suggestive of lipoblastic differentiation. Others have eosinophilic granular cytoplasm. There is no pleomorphism and mitotic activity is low.

The amount of mature adipose tissue within the tumor is variable and can be focal or extensive. The background matrix is myxoid and may show zones of hyalinization. There may be areas of hemorrhage, hemosiderin deposition, dystrophic calcification, or even ossification. The vascularity is prominent and consists of thick-walled vessels as well as cavernous spaces.

Ultrastructural and immunohistochemical studies on tumor cells have shown a range of differentiation ranging from features reminiscent of chondroblasts to prelipoblasts, lipoblasts, preadipocytes, and mature adipocytes. The tumor cells are S100+ and may show focal immunoreactivity for CD68 and cytokeratin. EMA is negative.

Molecular Genetics: Chondroid lipoma contains a balanced translocation t(11;16)(q13;p12-13) resulting in the fusion of C11orf95 and MKL2 genes.

Image courtesy of: Andy Zhang, MD, Dept. of Pathology, Rushan People's Hospital, Rushan City, Shandong Province, China.