What Does This MRI Report Indicate?

I had an MRI done in 2010 that came up with white matter that was 3.0 mm in size located in the posterior pituitary gland in the midline immediately posterior to the infundibular stalk. Another MRI that was recently done in December of 2014 says that white matter spot is now 4.3 mm. in size. Should I be concerned with that amount of growth in that period of time?