small ovoid opacity in the suprahilar area

i've been experiencing back pain and nape pain so i decided to have a check up..my attending physician suggested that i undergo a chest x ray (PA) view..i was confused with the remarks of my xray result.. " a small ovoid opacity is noted in the left suprahilar area "..the doctor suggested that i should undergo the same xray 6 months later..i was confused why should i undergo the same procedure again..what is really meant by this..please help me interpret this..tnx