Subcutaneous fat necrosis of the newborn: light, ultrastructural and histochemical microscopic studies.

Multiple subcutaneous plaques and nodules appeared on the back and the dorsal proximal area of the extremities of a 9-day-old male infant after a complicated prenatal period necessitating cesarean section. The clinical and histological features were diagnostic of subcutaneous fat necrosis of the newborn. Light microscopy revealed adipocyte necrosis, a lymphohistiocytic infiltrate, and needle-shaped clefts within adipocytes and macrophages. Ultrastructurally, there were aggregations of electron-lucent spaces in the form of spindles and needles arranged in parallel within the altered adipocytes; macrophages surrounded these cells or their fragments and invaded the fat lobules. Enzyme histochemical staining, not previously reported in the literature, showed that acid phosphatase, leucine aminopeptidase, and indoxyl and non-specific esterases were present in the areas of fat necrosis.