Abnormal cells found in breast cyst on cytology. cannot be seen on ultrasound due to aspiration so cannot do biopsy. would mri help?

Get with pathologist: A cell from a cyst aspirate maybe "abnormal" but with no malignant potential. The fact that the cyst is gone without a trace suggests to me that if your physician is good with this, watchful waiting may be safe and wise.

Yes.: If the MRI is negative the likelihood of cancer is less than 2%. If an MRI is not obtained, a follow up ultrasound examination should be obtained and, if the cyst recurs, a core needle biopsy of it may be indicated. I assume you have had a mammogram? If not, one should be obtained.