Can a CT and MRI without contrast detect a pituitary tumour?

Yes it could. Ct is more dependent on contrast. But MRI has two phases(t1and t2) which can serve like a contrast and the tumors often show up better in t2 weighted images.
Possibly. Possibly, if those studies show an enlarged pituitary gland with a mass within it. However, most commonly, only a well conducted and timed contrast administration, preferably with MRI would allow to visualize a pituitary tumor within the gland, as the tumor enhances with a slight delay compared to normal pituitary tissue.