Kidney Cysts (Renal Cysts): Symptoms, Diagnosis And Treatment
Kidney Cysts On CT Scan
Kidney cysts are a common finding on CT done for any reason. Most of the time they are benign and do not need treatment, Kidney cysts can be completely filled with fluid or have other more complex areas inside like thickening of the wall, nodules or septations. Kidney cysts can range in size from barely visible to enormous, pushing adjacent structures and causing pain. In rare cases, cysts can rupture.
Some kidney cysts are more concerning because they are more complex then simply containing fluid. A CT done without contrast injected through your vein does not completely evaluate a cyst. Since cysts are so common, many radiologists will diagnose a cyst on a CT without contrast and not require further testing unless they see something suspicious.
Kidney cysts are best evaluated on a CT with contrast injected through your vein. The radiologist will then see if parts of the cyst show complex areas or enhancement. Enhancement after contrast injected through your vein means that that part of the cyst is solid and not a cyst. This is more concerning for a cancer.
Cysts can also fall into a grey zone where we’re not sure if they are benign or malignant. Radiologists use a published Bosniak criteria to grade the cyst based on its suspicion, with lesions graded as 1 are benign and 4 as cancerous. Some lesions may show some features that are concerning but not clearly cancerous. These lesions may be followed (Bosniak 2F) or if more concerning (Bosniak 3) treated like a cancer with the knowledge that some will end up being benign.
The treatment of a Bosniak 3 or 4 graded cyst is partial or complete removal of the kidney. A Urology doctor will guide the management. Those cysts that fall into category 2F will be followed. Lesions graded as 1 or 2 are left alone. Sometimes an ultrasound or MRI may be suggested for certain cysts to further evaluate.
Kidney Cysts On Ultrasound
Ultrasound is frequently used to evaluate the kidneys and any cysts or masses. It may also be ordered if your doctor is concerned about how well the kidneys are working or if there is blood in the urine. Ultrasound uses high frequency sound waves to form an image. This is a painless test which uses no radiation. The quality of an ultrasound is dependent on the skill and experience of the technologist who performs the test, and the radiology doctor who interprets it. Sometimes the radiologist may want to see the cyst by watching the technologist scan in real time.
A kidney cyst is a benign mass that is filled with fluid. A simple cyst on ultrasound will have simple black appearing fluid inside, with a thin defined wall, and acoustic enhancement along the back wall (a white shadow going beyond the back wall). A cyst can also look complex with areas of thickening or modularity along the wall, or complex looking fluid. In these cases, the radiologist may recommend another test like CT or MRI to further evaluate.
The distinction between a simple cyst and more complex lesion is critical. Simple cysts are left alone and are benign. More complex lesions that contain more then simple fluid may be cancerous at times. Other tests like CT or MRI help assess the risk of cancer in these cysts. There is even a classification system called Bosniak which grades cysts from 1 to 4. Bosniak 1 cysts being benign all the time to 4 which are cancerous.
The ultrasound is sometimes limited in obese patients. The sound waves have a hard time penetrating large amounts of tissue and fat, and may make a simple cyst look more concerning then it really is. A CT or MRI will often help clear up any concern.
Small cysts, say less then 1.5 centimeters can also be a challenge. These small cysts may not have all the classic features of a simple cyst. The uncertainty can often be cleared up with a dedicated CT of the kidneys with thin sections going through the cysts done with and without contrast. In some cases when the cyst is not entirely simple but slightly complex, the radiologist may recommend a 6 month follow up to reevaluate the cyst.