Prepubertal gynecomastia with lobular differentiation.

We report the case of a 19-month-old African American boy with a unilateral breast mass that developed shortly after birth. A sonogram confirmed the presence of a "fatty" breast mass. Microscopy of the subcutaneous mastectomy specimen revealed florid gynecomastia with marked ductal hyperplasia and focal lobular differentiation. This exceptional example of prepubertal gynecomastia with lobular differentiation has been previously reported only four times in the literature. We report a fifth patient, as well as the youngest, with this unusual histologic finding.