Is it necessary to have biopsy after having mri? what is lymphnodes?

Sometimes: Lymph nodes are part of the immune system. They are located through out the body. They act sort of as filters. They can get enlarged for many reasons. Sometimes they need to be biopsied to figure out what has made them increase in size. An MRI is a way of taking pictures inside the body. Many times that is all we need, but many times we need more info like a biopsy.

Well yes: An MRI is a non invsaive test. It shows your anatomy and blood flow if they use contrast. When you see a suspicious lesion it is like all tests - you can't be sure what it is untill you get a piece of tissue. Basically they use the MRI to screen the part of the body they are looking at and any areas they consider highly suspicious for tumor might need a biopsy. Any enlarged lymph nodes also.