What it means
Ill-defined describes the edge of a finding, not what it is. The border fades gradually into the tissue around it rather than forming a clear line. This happens when a process spreads into its surroundings, as inflammation and infection do. It can also happen when a finding is small, faint or blurred by movement. The opposite is well-circumscribed.
When it matters
Ill-defined edges are common with infection, inflammation, swelling and healing tissue. Some tumors also grow into nearby tissue and look ill-defined. That is why indistinct edges on a breast lump are usually checked with a biopsy. Elsewhere, radiologists weigh the edges with your symptoms and other features. If infection is likely, a repeat scan after treatment often shows whether the area has cleared.
Questions to ask your doctor
- What is the most likely cause of the ill-defined area on my scan?
- Could this be an infection or inflammation that will clear?
- Should the area be rechecked, and after how long?
