Most of the kidney (renal) masses referred to the Division of Urology at Washington University School of Medicine are found incidentally when patients are evaluated for other indications. For example, a primary care physician may order a CT scan or an ultrasound of a patient who complains of abdominal pain. The scan may or may not reveal the source of the pain, but the scan identifies a growth (mass) arising from the kidney. Most of the masses found this way have no symptoms.

The most common renal mass is a cyst, or fluid-filled sac arising from the kidney. Half of the people over age 50 will have a cyst. Cysts are common and do not typically cause problems or carry any significant health risks. Most cysts are easily identified by the radiologists and can be classified as simple cysts, which don’t need intervention, and may not even need further follow-up or observation.

However, some cysts can be complex and present a greater diagnostic challenge for radiologists. Patients with mildly complex cysts can be followed with periodic imaging (CT, MRI or ultrasound) to monitor for growth and change in characteristics of the cyst.

Solid masses are worrisome for cancer; radiologists easily identify these. These masses are cancerous about 80% of the time. About one in five masses with characteristics suspicious for cancer on the imaging test will not be cancerous, but is generally treated with the expectation that it is cancerous.

Occasionally a CT- or ultrasound-guided biopsy of the mass is recommended to evaluate the mass more thoroughly. Sometimes a biopsy is helpful in guiding further therapy. However, the biopsy is frequently not as helpful as one might think. If the biopsy shows cancer, as predicted by the scan images, the subsequent management has not been altered and surgery or ablation is required. On the other hand, when the biopsy does not show cancer, frequently a definitive diagnosis on the mass cannot be made. This can happen because the tissue sample obtained is insufficient for the pathologist to make a clear diagnosis. Again, in this situation the biopsy has not been helpful, and surgery or ablation of the mass is required. Thus, in most cases, if the mass is suspicious for cancer, surgery or ablation of the mass is recommended without a biopsy.

In the majority of cases, minimally invasive, kidney-sparing procedures can be offered to patients. These treatment options include percutaneous, CT-guided cryoablation (freezing) of the mass, laparoscopic partial nephrectomy and robotic-assisted laparoscopic partial nephrectomy.

In some cases, the surgeon may recommend an open partial nephrectomy if the case is deemed to be too complex to be handled laparoscopically. In some cases, removal of the entire kidney (radical nephrectomy) is required and can usually be performed laparoscopically.