I have always thought of mammograms as similar to fingerprints. If you see a fingerprint on a glass or a tabletop you recognize it as a fingerprint. But that fingerprint is different from all other fingerprints. Likewise, when a radiologist looks at a mammogram it is recognizable as a mammogram but it is different from every mammogram he or she has ever seen before. The radiologist must therefore determine whether that mammogram falls within a range of normal, or if there is some feature that makes it abnormal.
The first thing the radiologist considers is comparing it to an earlier mammogram. It is extremely valuable to see a mammogram of the same patient from one, two, or even three years earlier to determine if there has been a change over that period of time. If there has been no change, there is a high level of confidence that that mammogram is normal for that patient. If, on the other hand, there has been a change, further investigation is typically warranted.
Sometimes the mammogram may be the first the patient has ever had or previous mammograms are simply not available. The radiologist must then decide whether further imaging is warranted at that time. Further imaging with more focused diagnostic mammography, ultrasound or MRI may lead to a recommendation for a biopsy or possibly a recommendation to repeat the mammogram after a short interval -- typically six months.
Radiologists use a shorthand number system called BIRADS. This stands for Breast Imaging, Recording and Data System. Radiologists can vary significantly when they describe something they see on a mammogram. To overcome this variability, the American College of Radiology asked the radiologist to assign a number to the mammogram after they have completed their description.
BIRADS 1 means that the image is entirely normal and there is essentially little to say. BIRADS 2 means that there is something specific to comment on but it is entirely normal. BIRADS 3 means that there is a feature to comment on but the radiologist feels that it is probably benign. BIRADS 4 means the feature that the radiologist is describing is causing concern and that the abnormality may be cancer. BIRADS 5 means the radiologist is quite certain a the abnormality is cancer. When the radiologist feels the imaging is incomplete and more studies are necessary at that time a BIRADS 0 will be assigned. BIRADS 6 means the image contains a biopsy proven cancer and the imaging is actually being done for some other reason.
The BIRAD numbers one through five are associated with recommended actions. BIRADS 1 and 2 are considered normal and annual follow-up is recommended. BIRADS 3 is probably benign and when the radiologist uses the term "probably" it means that there is a 98% certainty that the lesion is benign. Due to the very small element of doubt, a six-month interval to repeat the image is recommended. The concern is not at a high enough level to recommend a biopsy.
BIRADS 4 means there is enough suspicion to recommend a biopsy. When the lesion is felt to be BIRADS 5 it means the radiologist thinks it is cancer and therefore a biopsy should certainly be performed.
Radiologists are extremely careful when they read mammograms. They never want to miss a cancer. As a result, if they have any concerns about the image, they may ask the patient to return for further studies. This may be a more focused mammogram called a diagnostic mammogram. This may involve special views with magnification or a different type of compression. Sometimes an ultrasound examination is recommended to further define an abnormality. Occasionally an MRI of the breasts is recommended.
When a patient is called back for further testing it typically provokes anxiety. 90% of the time however the subsequent studies will result in a benign reading. Less than 10% of the time will the subsequent studies result in a recommendation for a biopsy and only a small percentage of those biopsies will result in a diagnosis of cancer.
Joseph J Casey, M.D.,FACS