Radiologist report for mri states, 4 mm region of hypoenhancement within the left aspect of the pituitary gland potentially reflecting a microadenoma. does this mean hes unsure or that results need to be combined with bloodwork for diagnosis?

Ask your physician about a blood test for prolactin, which is elevated with enlarging pituitary tumors, then see a neurosurgeon if prolactin levels are highly elevated.

Have NO clue if the radiologist is "unsure", but your description of the MRI suggests a "microadenoma". Endocrinology studies should indeed be done to assess the effect of this small tumor, which may or may not be affecting the endocrine system. You are urged to have a thorough discussion with your doctor regarding the next steps.