Receiving news that a screening mammogram is inconclusive can immediately cause significant anxiety. This result does not represent a diagnosis, but rather means the initial images were insufficient for a full assessment. It indicates the radiologist requires additional information to confirm whether the tissue structure is normal or requires further investigation. While this uncertainty is stressful, it is a common outcome, and the vast majority of these call-backs do not ultimately indicate the presence of cancer.
Defining the Inconclusive Result
The official reporting standard for an inconclusive mammogram is Breast Imaging-Reporting and Data System (BI-RADS) Category 0. This clinical designation specifically means “incomplete assessment” and necessitates further evaluation. A Category 0 finding communicates that the initial screening was technically limited or revealed an area needing clarification. The radiologist cannot confidently assign a final category until more specialized imaging is performed.
Common Causes of Ambiguity
The most frequent reason for an inconclusive result is the presence of dense breast tissue. Dense tissue contains a high proportion of fibroglandular elements and less fat, appearing white on a mammogram. This makes it difficult to distinguish from potential masses, which also appear white, and can effectively mask small abnormalities. Ambiguity may also arise from technical factors, such as slight patient movement or sub-optimal positioning, which can blur a specific area.
Another common cause is the summation artifact, where the normal, three-dimensional overlapping of breast structures mimics a suspicious mass on the two-dimensional image. Benign findings, such as simple cysts or calcifications, can also lead to an inconclusive result. Although harmless, their appearance sometimes requires additional, focused imaging to confirm that their shape and pattern are definitively non-cancerous.
The Immediate Next Steps
To resolve a BI-RADS 0 finding, the physician will order a diagnostic imaging work-up, typically beginning with a Diagnostic Mammogram and a Breast Ultrasound. Unlike the screening mammogram, a diagnostic exam is directed by the radiologist in real-time and focuses on the specific area of concern. The diagnostic mammogram often uses specialized techniques, such as spot compression and magnification views.
Spot compression applies focused pressure to separate overlapping tissue structures and clarify whether an apparent mass is real or an artifact. Magnification views are used to analyze microcalcifications, providing a detailed view of their size, shape, and distribution pattern. The breast ultrasound uses high-frequency sound waves to create a picture of the tissue and is effective at determining the composition of a mass. Sound waves pass through fluid, confirming if a finding is a simple, non-cancerous cyst, while a solid mass indicates the need for further evaluation.
Understanding the Final Outcome
Once the diagnostic imaging is complete, the radiologist assigns a definitive BI-RADS category, providing the final outcome. In the majority of cases, the finding is resolved as benign, resulting in a BI-RADS 1 (Negative) or BI-RADS 2 (Benign Finding) assessment. This means the patient returns to a routine annual screening schedule.
In a small percentage of cases, the diagnostic work-up confirms a finding that is either probably benign (BI-RADS 3) or suspicious (BI-RADS 4 or 5). A BI-RADS 3 finding has a low likelihood of being cancer (less than 2%) and often leads to a recommendation for short-interval follow-up imaging in six months. Outcomes classified as BI-RADS 4 or 5 are highly suspicious and require a biopsy to obtain a definitive cellular diagnosis. Even among those who proceed to a biopsy, most findings are ultimately confirmed to be non-cancerous.