What it means
Most kidney cysts are simple: a thin-walled bubble of fluid. The Bosniak classification, used on CT and MRI, rates how complex a cyst looks. The more internal walls (septa), thickened areas or solid parts that take up contrast, the higher the category. The categories are I, II, IIF, III and IV. On ultrasound, a cyst that is not clearly simple is usually checked with CT or MRI.
When it matters
Categories I and II are benign and need no follow-up. IIF (F for follow-up) is very likely benign but is rechecked with scans, often over several years. III is indeterminate: around half turn out to be cancer. IV contains solid enhancing tissue, and most are cancers. Cancers found this way are often slow-growing. III and IV are usually discussed with a urologist, who may suggest surgery or close monitoring.
Questions to ask your doctor
- Which category is my cyst, and which features put it there?
- Does my cyst need follow-up scans, and how often?
- Would a CT or MRI with contrast clarify the cyst seen on ultrasound?
Read more: Renal Cyst: What It Means on Ultrasound and CT, Causes, and When to Worry
