Ultrastructure of lipoma.

Eleven benign lipogenic tumors comprising ten ordinary lipomas and one fibroblastic lipoma were studied by light and electron microscopy. The former, which contained only a few inconspicuous septa, were composed of univacuolar mature adipocytes. No young forms of adipocytic differentiation were seen reflecting the slow growth of the ordinary lipomas. Small spindle cells accompanying capillaries located in the triangular confluence of the adipocytes are thought to be potential precursors of adipocytes. By contrast, the fibroblastic lipoma contained many younger forms which closely resembled those seen during maturation of normal adipose tissue. These younger forms are located in and about prominent trabeculae which therefore are considered to constitute active growth centers.