I have a movable round lump in my right arm pit. breast mri showed no lymphendenopathy and similar in appearance to left side. they also did an ultrasound and said unremarkable and did not do a biopsy. i am still concerned.

Mass: A palpable cyst or solid mass would generally be easily seen on ultrasound or MRI. Pathologic adenopathy is also readily seen. So the two most likely possibilities would be a normal lymph node that is superficial enough to feel, or a benign lipoma, which is a soft fatty tumor that may have a capsule so thin it can be indistinguishable from adjacent normal fat on imaging. Talk to your doc.