Callback from clinic and physician for second mammogram, why is this?

To check further: Sometimes the radiologist identifies an abnormality on a mammogram for which additional mammogram images are needed called a diagnostic mammogram. It is also possible that an ultrasound may become needed and on rarer occasions an MRI may be suggested. Please follow thru with the radiologist's recommendation to clarify the issue.

The radiologist: identified a potential abnormality on the screening mammo, and it requires special additional views and possibly ultrasound to completely evaluate. This scenario occurs with approximately 10% of screening mammos, and once the additional imaging is performed, about 80% of the time it is nothing of concern.

A difference: in density or an area of uncertainty is seen and they want to take more views of the area to see if there is anything of concern or not. About 80% of the time it turns out normal.