Indeterminate kidney lesion on an imaging test means we don’t know exactly what a spot in the kidney is. The lesion or abnormality can be something that is benign and can be left alone. It can also be something dangerous to health or cancerous and needs to be removed surgically. The radiologist who read the test is trying to convey that the kidney lesion or abnormality needs to be further analyzed by other imaging tests or followed closely with tests in the future.
I see indeterminate kidney lesions most common on CT scans of the abdomen. Many of these abnormalities are tiny, less than a than a centimeter and too small to say what they are. Other kidney abnormalities are not simple cysts and have complex internal appearance. Some kidney abnormalities seen on CT done only without contrast or with contrast (dye given through the vein) is not enough to say what a kidney abnormality is. Other tests such as ultrasound or MRI can also have this result. X-rays rarely show kidney lesions unless they are calcified.
The best test in my opinion to determine what exactly a kidney abnormality is a dedicated kidney CT. Sometimes an abdominal MRI will also be done for this purpose. An ultrasound is also very good at telling if a kidney abnormality is a cyst or solid lesion. It also offers a very detailed look at the internal contents of the abnormality. All these tests are complimentary and offer additional information which can help with making an accurate diagnosis.
The CT will involve scanning the kidneys before giving contrast or dye through a vein and after. A more delayed phase is also obtained when the kidneys are excreting the contrast into the ureter and bladder. Often thin sections are obtained through the kidneys which is helpful to see fine detail and for smaller abnormalities. The CT test is also easier and quicker. An ultrasound will depend on the skill of the technologist. It’s also not the best for big patients. An MRI will require cooperation with breath holds and is a longer test.
The most concerning feature of a kidney abnormality is contrast enhancement. This means that the tissue in the kidney abnormality takes up the dye given through your vein. Benign cysts won’t do this. They are basically made of water. Cysts can also be cancerous but are usually more complex in appearance than simple water.
The kidney lesion taking up dye means that the kidney abnormality is made of solid tissue which is concerning for a tumor. Tumors can be benign or cancerous. Some features like internal fat can help the radiologist dinstinguish between these possibilities. Other times, the lesion will have to be removed. Kidney abnormalities are rarely biopsied in my experience.
An indeterminate kidney lesion therefore means we simply don’t know what it is and needs more testing or even follow up. Sometimes even after testing, we don’t know what it is. Usually these lesions will be followed closely for any growth or change or removed depending on the appearance.
Cysts can be benign and not of any concern. Others will need to be followed or even removed. Solid lesions will have to be removed unless they have fat inside them which makes them benign angiomylipomas. Some solid lesions of the kidney can also be benign, like oncocytoma. The diagnosis is rarely made before surgery. An old exam you may have had can also be helpful. Something in the kidney which has not changed for years is likely benign although some kidney cancers can be slow growing.