Subcutaneous fat necrosis of the newborn with emphasis on ultrastructural studies.

The morphologic examination of neonatal subcutaneous fat necrosis is reported. Subcutaneous nodules after prolonged labor and asphyxia appeared in the skin of the back and neck. Biopsy was performed at 16 days. The infants' general state did not change and the nodules spontaneously regressed. Light microscopically focal necroses of the subcutaneous adipose tissue were present, with granulation tissue. Electron microscopy revealed complex material replacing the necrotic fat cells. Two types of crystals could be observed: short, rectangular ones irregularly arranged and long, needle-shaped ones, parallel or radial in arrangement. The dissolved lipid crystals were surrounded by membranes that probably arose from the necrotic fat cells. The crystals passed the cytoplasm membrane of the macrophages. Giant cells arose from macrophages, partly by fusion of the cells and partly by amitosis.