Kidney Mass
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A CT scan ("Cat scan") depicting a mass of the left kidney (on right of screen) Kidney masses can be solid or cystic with the majority of solid masses being malignant (cancer) |
Urology Care Foundation's video on kidney masses (press play for more information)
It is important to speak to your doctor about your specific situation as there could be variations in protocols. This is not meant as a substitute for medical care. It is a supplement to your discussion with me.
A common urologic problem is masses of the kidney. Masses of the kidney are typically tumors (an abnormal growth of cells) with both terms being used interchangeably when referring to solid growths of the kidney. However, a mass of the kidney could also signify a cyst (a fluid filled structure) that changes the normal anatomic appearance of the organ. Tumors are typically solid structures and cysts are usually hollow and fluid filled, yet depending on the imaging study performed, they may both be labeled "mass."
Kidney cyst (left) in comparison to a solid kidney tumor (right)
Kidney cysts are overwhelmingly benign and almost always do not require intervention. There are some special considerations when cysts are characterized as complex on imaging. This suggests that the cyst may have abnormal features that do not make it a simple cyst. Abnormal features that connote complexity such as calcifications, solid components or enhancement (image finding suggesting independent blood supply) raise the suspicion of cancer in the cystic mass. Depending on the complexity, some cysts may need monitoring over a period of time to ensure it doesn't become more suspicious and some cystic masses may even require surgical removal.
The fact remains: the majority of kidney tumors are cancerous. Multiple studies have shown that close to 70-85% of excised kidney masses are indeed found to be cancerous with the remaining 15-30% of tumors being benign. The variation in numbers exist because of different research studies arriving at different conclusions (this is typical of medical studies). But the take home message is: the majority of kidney tumors are cancerous. Given the high likelihood of cancer being present in a solid tumor of the kidney, the safest approach is usually to remove it.
Thus, the discussion of kidney tumors is undoubtedly a discussion about the risk of kidney cancer.
Normal kidney (left); Kidney with a tumor at the upper pole location (right)
Kidney cancer stages. Note the increasing size of the tumor and spread with increasing stage.
In 2016 there was an estimated 62,000 cases of kidney cancer diagnosed in the United States, of which an estimated 14,000 will die from the disease. Based on data from 2013, the overall survival rate for all stages of kidney cancer was approximately 74% (average of all comers with kidney cancer). Naturally, the survival rate is higher for earlier stages. The incidence of kidney cancer is increasing by about 1% a year. This is probably due to people living longer than before and the rise of CT and MRI scans of the body for other reasons (which pick up incidental masses).
Here is a table from the World Health Organization that lists all of the different types of tumors that can occur in the kidney:
The list is certainly long but the takeaway message is that the most common malignant tumor of the kidney is renal adenocarcinoma (cancer) of which the "clear cell" variant is the most common.
Kidney cancer is more commonly found in men than women. This is likely due to more men smoking than women. Smoking is the biggest risk factor for developing kidney cancer. It is estimated that smoking will increase a man's risk of developing the disease by 50% and a woman's risk by 20% over their lifetime! Obesity, hypertension, exposure to certain harmful chemicals, end stage renal disease and some familial (genetic) diseases also may increase the risk of kidney cancer over a patient's life. As for prevention of this cancer, it is imperative to stop smoking tobacco. Tobacco cessation will also increase overall life expectancy and decrease the risk of developing urologic cancers.
Kidney cancer is most common in the 6th-8th decades of life. Thus it is a disease associated with the elderly. Close to 10% of cases will present with a "triad" of signs: flank mass, hematuria and pain. Unfortunately, because kidney cancer typically does not present with any symptoms and is usually discovered accidentally, nearly 30% of the cases present with metastatic disease (cancer that has spread outside of the organ of origin).
Work-up
Your doctor will begin with a simple work-up that will include a history & physical examination (including a careful family, medical and surgical history), laboratory work (including a CBC and CMP test to check to see if your body is potentially responding to a kidney cancer), urine tests and imaging studies. Imaging studies such as a CT scan with a "renal protocol" or MRI will help guide your urologist to a plan. These imaging tests will show a clearer picture of the mass as well as its size, location and the extent of its spread. Seldomly, both studies may be indicated depending if there is concern for involvement of the renal vasculature (ie, renal vein thrombus, etc).
Many patients will come to the office with the initial study that caught the mass. However, a confirmatory imaging study with a CT or MRI is needed to get the best possible picture. If one has been performed but there was not contrast administered, it'll have to be repeated as well. The contrast that is given intravenously is to see if the mass "enhances." Enhancement means the mass gets brighter than its surroundings suggesting it has it's own blood supply. This is characteristic of kidney cancers and it's why these imaging tests usually need to be repeated. This is also imperative if surgery is being considered as it allows the surgeon to map out a "game plan" to remove the tumor with minimal trauma to the surrounding structures.
Renal Mass Biopsy
Occasionally, a renal mass biopsy may be ordered by your doctor.
Renal mass biopsy is becoming more established as part of the management of suspicious renal masses however there are some caveats. In the past, the indications were reserved for evaluation of metastatic disease, lymphoma of the kidney and abscess (infection). However, now in the contemporary era, renal mass biopsy is being used to identify potential benign masses and on the frail and elderly population to potentially avoid aggressive treatment.
The reported accuracy rates of a biopsy vary with most studies reporting over 90% accuracy in determining if a tumor is malignant or benign, with low complication rates, minimal risk of tract seeding (<0.01%) and low false negative rates (<5%). Repeating a biopsy if the initial one was non-diagnostic can be done safely with a diagnostic accuracy rate of about 80% on repeat.
However, there are real limitations to renal mass biopsy, which is why in the majority of cases they are not ordered by your doctor. First, nothing is 100%. Even at its best, the accuracy rate of a biopsy may not be enough to comfortably ignore a mass forever. Second, if the biopsy is nondiagnostic, it doesn't mean that it's benign, rather there is not sufficient information to guide therapy. Third, if the biopsy comes back as benign, it may be difficult to accept there was not a sampling error or that the results are representative of the entire mass. Thus, most times, renal mass biopsy may lead to more questions than answers, and is instead reserved for special circumstances.
If choosing an ablative treatment, such as cryoablation, a renal mass biopsy is done at the time of the therapy.
Treatment Options
Active Surveillance
Monitoring the mass over time is known as active surveillance. A similar treatment approach exists for prostate cancer as well. In this scenario the surgeon and patient have elected to hold off on definitive treatment (such as surgery or ablation) and instead monitor the mass for changes in size or complexity. This may be a temporary approach with eventual treatment of the mass in the future. The reasons for this can be numerous, but usually a mass is monitored because it is small (suggesting a benign process), a patient is medically frail (thus an aggressive surgery or kidney removal would be prohibitively dangerous) or the patient wishes to wait for other reasons. There may also be times when the patient has another medical problem or malignancy being treated (ie, leukemia, lung cancer, etc) and has to wait for the completion of therapy before proceeding with definitive therapy for the kidney mass. The take home message here is that the mass is typically monitored until there are more definitive signs that the mass is cancerous and therefore treatment is held off (sometimes indefinitely depending on the circumstances).
There are a lot of variations of active surveillance protocols. Surgeons usually will choose to see their patients back in 3-6 months for the second visit, followed by every 6-12 months depending on the patient and tumor characteristics. Tumors typically will grow at a rate of 0.1 to 0.7 cm a year, depending on the size and pathology. It has been reported that up to a third of the masses will not grow in a given year. Lack of growth does not necessarily mean the tumor is benign however it is reassuring. The literature reports that for about 50% of the active surveillance tumors that eventually end up being treated, about 90% are indeed cancer.
The take home message here is active surveillance remains an acceptable strategy for small masses and for those with serious medical comorbidities where definitive treatment would be very risky (ie, severe congestive heart failure, respiratory compromise, anticoagulation, severe liver disease, etc).
Surgery
Kidney cancer is known as a surgical disease. In other words, the best treatment option is usually surgical removal. Surgery offers the best long term cure and also provides a pathological specimen for confirmatory tests. Once the tumor is removed the pathologist can render a diagnosis based on the histology of the entire mass and assess the margin (the very limit of the tumor) for tumor extension. This provides invaluable feedback to establish a follow-up regimen or to determine if secondary treatments are needed.
Whether to perform surgery or not depends on several important factors, including whether the kidney tumor is localized to the kidney only (and has not spread or metastasized), if surgery is technically feasible and if the patient is healthy enough to undergo an abdominal operation and anesthesia. The two surgical options are radical nephrectomy and partial nephrectomy.
Radical nephrectomy means removal of the entire kidney with the tumor. This is typically reserved for large tumors (larger than 4 cm) or when partial nephrectomy is not technically feasible for smaller masses. It may also be indicated if there is extension into the kidney's veins or if the tumor shows signs of advanced disease (ie, invasion of surrounding structures, tumor thrombus, etc). Radical nephrectomy may be chosen by the surgeon as well if the patient has serious medical comorbidities and requires a faster operation in order to shorten the operative time and/or time under anesthesia. A radical nephrectomy may also be performed if there is a complication during a partial nephrectomy (ie, bleeding, instability, etc).
A person can live a normal healthy life with just one normally functioning kidney (this is why healthy patients can donate a kidney for transplantation) however having a solitary kidney is not without compromises and requires a patient keeps a healthy weight, blood pressure along with consistent medical follow-up.
This approach can be accomplished through a minimally-invasive approach, such as laparoscopy or even robot-assisted laparoscopy (da Vinci robot), as well as a more traditional open approach. This is usually at the discretion of the surgeon with cancer control and survival rates being the same for all approaches used.
Compared with partial nephrectomy (see below), radical nephrectomy has a lower rate of overall complications including hemorrhage (1.2 vs 3.1%), urine leak/fistula (0 vs 4.4%), and reoperation for complications (2.4 vs 4.4%) based on data reported in a large phase III randomized control trial (EORTC 30904). However, radical nephrectomy does increase the risk of developing chronic kidney disease which can be detrimental in the long term depending on a patient's specific medical picture.
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| Conceptual goal of radical nephrectomy (clipped renal vasculature & proximal ureter) |
A partial nephrectomy means partial removal of the kidney with the tumor. It is also known as nephron-sparing surgery. This is the standard of care for small kidney tumors (less than 4 cm). It requires the surgeon remove the tumor along with a small rim of normal tissue, called the surgical "margin." The margin is then studied by the pathologist to determine if all of the tumor was indeed removed. In other words, a margin with infiltrating tumor/cancer suggests the possibility of cancer remaining behind. Partial nephrectomy is also an alternate care strategy for larger masses when there is a strong need to preserve global renal function (such as with patients with a solitary kidney or advanced kidney failure). It is also the standard for bilateral kidney masses.
Partial nephrectomy has equivalent oncologic success rates compared to radical nephrectomy. Although the open approach is the classical method, laparoscopy and robotic-assisted laparoscopy are being increasingly utilized with similar success rates compared to the open approach. There is increasing debate as to whether a partial nephrectomy improves overall patient survival, in comparison to radical nephrectomy, given the preserved renal function, however a large randomized control trial (EORTC 30904) did not support that conclusion. Nonetheless, for a healthy patient with a smaller mass, it is usually the recommended approach in order to preserve as much renal function as possible.
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| Conceptual goal of partial nephrectomy followed by renorrhaphy (repair of normal tissue) |
Ablation
Ablative technologies exist for small renal masses. These are technologies that aim to destroy the abnormal tissue with a minimally invasive technique, such as introduction of a set of needles that can deliver cold gas to freeze the tissue (cryoablation) or high-energy to burn the tissue (radiofrequency ablation). The minimally invasive approach is typically percutaneous (through the skin) however some tumors require an open surgical approach or laparoscopic approach to ensure surrounding structures are not injured.
Ablation is usually reserved for patients who are not surgical candidates. This is because in comparison to surgical removal the literature is weaker in support of ablation as a standard of care. Although it is still an option, it is not as effective as surgery for cure when comparing success rates to surgical removal. There is unfortunately a higher risk of local recurrence, potential need for repeat intervention (repeat ablation vs definitive surgery), and increasing the complexity of a salvage surgical procedure (salvage indicates that one initial therapy has failed and the tumor has continued to grow). Follow-up regimens are also variable and may require frequent repeat CT or MRI scans to monitor the mass for any changes. It could be difficult to know if the treatment worked since the mass is technically still there. Therefore it takes multiple imaging studies over time to see if the mass changes (shrinks or disappears vs grows). Nevertheless, it is still an option in special circumstances, especially if the patient has high medical risk and the mortality of risk of surgery is too high. Long-term efficacy data is still pending, but urologists believe these technologies have a promising future.
Renal function is preserved with ablative technologies in a similar fashion compared to partial nephrectomy.
Kidney mass biopsy with cryoablation (freezing) of tumor
Conclusion
Masses of the kidney can either be cystic or solid tumors. When solid, it signifies a higher risk of cancer presence and must be worked up by a urologist. The work-up will include a full evaluation with laboratory work and confirmatory imaging studies. Once this is performed, your urologist will discuss treatment options, including active surveillance, radical or partial nephrectomy, or even possibly ablative technologies. For healthy patients, the best treatment option is surgical removal, with partial nephrectomy being the standard of care for smaller kidney tumors. It is imperative to ask questions about success rates, risks of complications, recovery time and follow-up regimens.
If you have any questions, please feel free to send me a message via my website: ricardogonzalezmd.com or call for appointment: Bradenton office 941-792-0340 or Lakewood Ranch office 941-747-2582.
If you have any questions, please feel free to send me a message via my website: ricardogonzalezmd.com or call for appointment: Bradenton office 941-792-0340 or Lakewood Ranch office 941-747-2582.
Knowledge is power. Thanks for reading!
Ricardo Dario Gonzalez, M.D.
Urology Partners of Bradenton
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