Fibroadenoma=the most common breast mass in adolescents and young adult women.
Fibroadenomas are painless, firm, mobile, slow-growing, solitary breast mass. It stays there over several menstrual cycles and may grow slowly.
Fibrocystic changes, on the other hand, varies in size during the course of a menstrual cycle. They can be painful and are usually bilateral.
Ultrasound is the imaging modality of choice for breast changes in pediatric population and young women.