Purpose or Case Report: Subcutaneous fat necrosis of the newborn (SCFN) is an uncommon disorder predominantly occurring in full-term and post-term neonates during the first 6 weeks of life. Clinically it presents as an area of edema followed by indurated plaques or non-tender and mobile nodules with overlying erythema, typically along the back, buttocks, extremities, or cheeks. SCFN may result from localized tissue hypoxia and mechanical pressure that further compromises the local circulation. Fetal and neonatal conditions including macrosomia, perinatal asphyxia, traumatic birth and therapeutic hypothermia; and several maternal conditions including preeclampsia, hypertension, gestational diabetes, cocaine or cigarette exposure, calcium channel blocker use during pregnancy, and familial dyslipidemia have been associated with SCFN. Although SCFN is a self-limiting condition, patients should be monitored for associated hypercalcemia and its complications such as nephrocalcinosis and nephrolithiasis.

As these lesions are superficial, they are well evaluated with high resolution ultrasound imaging for initial assessment and follow-up. Findings on ultrasound and MRI include lesions confined to the subcutaneous fat sparing the dermis, with indistinct borders lacking a distinct mass. Lesions of SCFN are echogenic on US, intermediate to low signal intensity on T1-weighted sequences, intermediate to high signal on fluid sensitive sequences, and may demonstrate cystic changes.

We will review the imaging findings of subcutaneous fat necrosis in over ten newborns collected from three tertiary care hospitals, with a focus on ultrasound findings. Many of the lesions were multifocal and the majority involved the patient's back. Ultrasound evaluation was performed in all cases. MRI performed in a minority of cases will also be reviewed. While only one case was biopsied for pathologic correlation, each lesion was closely followed clinically. We will also review several mimickers of fat necrosis to be aware of.
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