It means that your doctor thinks that an enlarged pituitary is a reasonable explanation for your symptoms and wants to have the images of the brain to look at he pituitary (and the rest of the brain).
The pituitary makes thyroid stimulating hormone (TSH), a problem with your pituitary could cause Hypothyroid (low levels of thyroid hormones).
All information from the eyes travels to the brain through nerves which pass very close to the pituitary gland. It is important to assess the pituitary with changes in vision including blurred or double vision, loss of vision in one or both eyes, drooping eyelid, or dilated pupil(s).
So the doctor has ordered an MRI of your brain -- and specified to pay particular attention to the orbits (area near the eyes) and blood vessels (MRA).
MRI of the orbits is obtained for a variety of reasons, and is the most accurate method in evaluating for pathology behind the orbits (retro-orbital), involving the optic nerves, chiasm, and optic tracts.
A magnetic resonance angiogram (MRA) is a type of magnetic resonance imaging (MRI) scan that uses a magnetic field and pulses of radio wave energy to provide pictures of blood vessels inside the brain.
You should call your doctor's office and have someone there tell you what your doctor meant by this. I one time had a strange notation from my doctor's office that made me think one thing, but the doctor meant the exact opposite of what I thought she meant.