RESUMO
Neonatal breast enlargement is a hormone-related condition, mostly asymptomatic\physiological, with a well-recognizable sonographic appearance but limited data in the literature. It can be uni-or bilateral. Typically described in the first week of life, the transient lesion disappears spontaneously within 6 months. The main differential diagnosis is neonatal mastitis, a breast tissue infection that requires a specific antibiotic therapy. Knowledge of clinical and imaging findings is crucial, and ultrasound represents a reliable tool which allows a quick identification and an excellent examination of neonatal breast abnormalities. We aim to highlight sonographic classic features of benign neonatal breast enlargement showing how ultrasound rules out real breast masses helping to differentiate between it and mastitis when clinical and laboratory data are inconclusive. We describe a 2-day-old male with bilateral breast swelling more pronounced on the right side.