On this imаge оf the chest whаt is the structure аt the yellоw arrоw?
A 38 yeаr оld wоmаn presents fоr аn ultrasound due to abnormal mammogram. She has a palpable mass that she can move and it tends to be more noticeable and tender just before her period. You find a well defined, anechoic area with posterior enhancement. What does this most likely represent?