What Does This Mammogram Indicate?

I am a 35 year old female and just had my baseline mammo. The results came back a mild area of asymmetry with parenchymal density in the medial posterior aspect of the left breast. The breasts are otherwise symmetric with no suspicious masses or calcifications. The radiologist suggested a six month follow up, my OB/GYN gave me the option for a six month follow up, or a consultation with a breast surgeon. Can you explain to me what this means? Thank You.