Subcutaneous Fat
Necrosis of the
Newborn
Subcutaneous fat necrosis of the newborn is a rare variant of localized lobular panniculitis that appears in newborns during the first days of life. From a clinical point of view, smooth, circumscribed, red to violaceous, subcutaneous nodules or plaques develop, sometimes symmetric, involving mostly the buttocks, shoulders, cheeks, and thighs Sometimes, infants affected by subcutaneous fat necrosis of the newborn have hypercalcemia or thrombocytopenia of unknown significance.The newborn has a relatively large body surface in comparison with his or her weight and a greater ratio of saturated to unsaturated fatty acids than in adult fat, and these two factors favor the release of hydrolases that induce breakdown of unsaturated fatty acids caused by minor trauma. Other etiologic factors that have been postulated in relationship with subcutaneous fat necrosis of the newborn include obstetrical trauma, induced hypothermia for cardiac surgery, gestational diabetes, hypoglycemia, Rhesus factor incompatibility, meconium aspiration, placenta previa, umbilical cord prolapse, anoxia, seizures, and preeclampsia. Rare examples of subcutaneous fat necrosis of the newborn have been described after prostaglandin E administration, in newborn infants with brown fat deficiency, in newborns with serum abnormalities of lipids and lipoproteins, in infants from mothers who used cocaine during pregnancy, as a consequence of the intrapartum administration of calcium channel blockers, and in association with thrombocytopenia. Usually, cutaneous lesions of subcutaneous fat necrosis of the newborn develop during the first days of life, although cases with congenital and ulcerated lesions that were already present at delivery have also been described.
SUBCUTANEOUS FAT NECROSIS OF THE NEWBORN AT A GLANCE
Clinical
· Circumscribed, red to violaceous, subcutaneous nodules or plaques on the buttocks, shoulders, cheeks, and thighs
· Sometimes, hypercalcemia or thrombocytopenia
Histopathology
· Mostly lobular panniculitis without vasculitis
· Dense inflammatory infiltrate composed of lymphocytes, histiocytes, lipophages, and multinucleated giant cells
· Narrow needle-shaped clefts, often in radial array within the cytoplasm of the histiocytes and multinucleated giant cells
Treatment
· Spontaneous resolution
· Etidronate in patients with hypercalcemia
The histopathologic picture of subcutaneous fat necrosis of the newborn is characteristic. It consists of a mostly lobular panniculitis, with a dense inflammatory infiltrate composed of lymphocytes, histiocytes, lipophages, multinucleated giant cells, and sometimes, eosinophils interspersed among the adipocytes of the fat lobule . Many adipocytes are replaced by cells with finely eosinophilic granular cytoplasm that contain narrow, needle-shaped clefts, often in radial array . These needle-shaped clefts represent crystals of triglycerides of the adipocytes; they are doubly refractile under polarized light and stain with oil red O. Some of these clefts may also be seen within the cytoplasm of multinucleated giant cells. The needle-shaped crystals in radial fashion within the cytoplasm of adipocytes and histiocytes are quite characteristic of subcutaneous fat necrosis of the newborn, but are not exclusive, because identical crystals have also been described in lesions of sclerema neonatorum and poststeroid panniculitis. Histopathologic differential diagnosis of subcutaneous fat necrosis of the newborn versus sclerema neonatorum is straightforward, because lesions of the former show a dense inflammatory infiltrate of histiocytes and lymphocytes in the fat lobules; whereas in lesions of sclerema neonatorum, characteristically, the inflammatory infiltrate is lacking.
In contrast to sclerema neonatorum, infants with subcutaneous fat necrosis of the newborn have an excellent prognosis, and spontaneous resolution of lesions is the rule, although a residual lesion of lipoatrophy may remain. Deaths have been reported in patients with associated hypercalcemia and, to avoid that, etidronate, a diphosphonate, has been proposed as an effective treatment.