From time to time, kidney masses are discovered in the size range of 3.5 to 4.0 cm or less in diameter.  Often such spherical lesions are found in the absence of symptoms-an "incidental" discovery. 

 

At other times they may be symptomatic, associated with abdominal pain or hematuria  (blood in the urine).  Small cancerous kidney masses represent early growths, and have a better prognosis than larger tumors. ^[1]

 

Small kidney lesions have become more common with widespread use of abdominal cross-sectional imaging, such as CT and MRI scanning.  When such studies are performed to evaluate abdominal issues, kidney masses are found incidentally on 13 to 27% of the studies.

 

The majority of these lesions are small benign cysts requiring no treatment.  Minorities of the small renal masses are complex and enhance with contrast material injection, suggesting cancer. 

 

When a small renal (kidney) mass is found incidentally, an evaluation is begun to determine the presence or absence of malignancy, and the therapeutic path.

 

Simple renal cysts are diagnosed by radiologic criteria, filled with fluid, and require no further work up.  A solid enhancing mass has a high probability (80%) of being malignant.

 

The smaller the mass, the greater the chance it is benign.  In a study of 2770 renal masses, 46% under 1 cm were benign, while 80% of those 3 to 3.9 cm in diameter were malignant. ^[1]

 

At the time of diagnosis, 1 to 8% of renal cancers measuring 3 to 4 cm in diameter were found to have spread (metastasized). 

 

Another study showed that metastasis was found in 5.2% of 8792 patients diagnosed with renal cell cancers measuring less than or equal to 4 cm.  The rate of metastases found at diagnosis increased 3.5 percent for each 1 cm increase in the diameter of the primary kidney cancer. ^[1]

 

Most excised small renal cancers exhibit low grade aggressiveness.  One study of 3 to 4 cm kidney cancers showed 14 to 26% were rated high grade in aggressiveness, and 12 to 36 percent had invaded locally into perirenal fat. 

 

Patients with small renal masses causing flank discomfort or hematuria have a worse prognosis than those with similar-sized masses.

 

Needle biopsy can be performed under CT guidance to identifies cancerous histology 80 to 92 percent of the time, with a specifity of 83 to 100 percent.  Smaller masses have higher false negative rates, which can be improved by repeat biopsies.  The risks of this procedure are low, for hemorrhage, and unlikely for seeding of the needle track.

 

If removal of a small kidney cancer is required, nephron-sparing resections are often employed in the modern approach, removing only a part of the affected kidney.  This allows preservation of dual kidney function, and is effective in cure and control of the primary cancer.  Forms of treatment include laparoscopic partial nephrectomy, open surgical, or robotic approach.  This is the standard nephron-sparing treatment option, supported by 15 years of solid follow-up data. ^[1]

 

Other therapeutic approaches include image-guided tumor ablation (freezing or radiofrequency ablation), radical nephrectomy (complete removal of the affected kidney), and active surveillance, in frail elderly, poor surgical risk, limited life expectancy, severe reduction in kidney function, or patient choice not to have invasive procedures.

 

The prognosis for individuals undergoing laparoscopic nephron-sparing surgery, as in robotic procedures, the 5-year cancer specific mortality was 2.4 percent, and at 10 years 5.5 percent.

 

The improved survival results from early (small tumor) diagnosis and well-tolerated, highly effective therapy.  Symptoms of blood in the urine and/or abdominal/flank pain prompt rapid medical examination and scanning of the renal beds and abdomen.

 

Prevention requires avoidance of kidney cancer carcinogens: cigarette smoking is the leading environmental toxin associated with this disease.  Additionally, obesity is associated with increase rates of kidney cancer. 

 

 

 

 

 

 

 

[1] Gill IS, Aron M, Gervais DA, Jewett, MAS.  "Small Renal Mass." N Engl J Med.  2010;362:62        

Notes: [1] Gill IS, Aron M, Gervais DA, Jewett, MAS. “Small Renal Mass.” N Engl J Med. 2010;362:624-34.

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