The mammographic mass has a circumscribed margin, most suggestive of a cyst. However, it has increased in size since the prior study and there are no other visible circumscribed masses in either breast (i.e. appearance does not fit the "multiple bilateral masses" category 1,2) - hence prompting further assessment.
At ultrasound, it was subtle, near isoechoic and superficial.
Both the mammogram and ultrasound appearances are compatible with a hemangioma, however given the relative infrequency of this diagnosis, other differentials would generally be considered first.