An Older Man With a Small Renal Mass

A renal mass was found incidentally in a 69-year-old man during his hospitalization for an episode of sigmoid diverticulitis. Abdominal CT scans with and without contrast demonstrated the presence of a 2.8 to 3.0 cm mass, peripherally on the left upper pole. The mass was cystic but contained numerous  fine septa, and it clearly enhanced  with contrast.

HISTORY
The patient has type 2 diabetes mellitus of 7 years’ duration complicated by significant peripheral neuropathy of both feet. He has no obvious signs or symptoms of heart disease, although the neuropathy limits his ability to walk. He does not smoke. He takes an angiotensin-converting enzyme inhibitor, metformin, and pioglitazone.

PHYSICAL EXAMINATION
Results of the examination are essentially normal except for mild central obesity and neuropathic findings in both feet. Specifically, no abdominal bruit, mass, or tenderness is noted.

LABORATORY RESULTS
Creatinine level is 1.4 mg/dL with an estimated glomerular filtrationrate of 68 mL/min. There is no proteinuria.

Which of the following statements about this case is true?

A. A radical nephrectomy  is the treatment of choice.

B. The malignancy risk as well as the pathological grade is related to the size of the lesion.

C. As a result of increased radiologic discover y of mass lesions, rates of death from kidney cancer continue to decline significantly.

D. The total mortality rate at 5 years  is less  than 10% in patients  such as this one.

CORRECT ANSWER: B

Our patient has a small renal mass, which is defined as a contrast-enhancing mass of 4 cm or less on abdominal imaging.¹ These lesions join the ever growing list of “incidental” findings detected on imaging studies usually performed for another reason. This case was very typical in that abdominal CT scanning for an episode of diverticulitis resulted in the discovery of an unrelated lesion in the kidney. In the past 25 years, radiologic detection of these asymptomatic lesions has increasingly become the way in which renal tumors are initially diagnosed (48% to 66%), including those renal tumors that require surgery (38%).² Any discussion of the entity involves 3 basic issues: the radiology of small renal masses, management options, and results of the above methods.

Radiologic classification. As with mammography, a detailed set of radiologic studies and criteria has evolved with a classification system that contains 4 criteria to categorize the malignant potential of small renal masses. A recent review of the topic contains pictorial examples and discussion of the various lesions.² In summary, they range from class I, definitively benign, to class IV, almost certainly malignant. Although not definitive, size alone is an important indicator of risk of cancer: the smaller the lesion, the lower the cancer risk. And, conversely, the larger the lesion, the higher the cancer risk and the higher the pathologic grade on biopsy.¹ Thus, choice B is true. Our patient has a 2.8 cm cyst with smooth walls and septa in which measurable enhancement is present; therefore, this mass is class III, indeterminate but with a clear risk of malignancy. A variety of management options exist in such situations.

Management options. Treatment and diagnostic decisions about small renal masses need to take into consideration patient status and comorbidity, renal function and, of course, patient preference (although in the author’s experience this almost always mirrors the treatment the physician prefers). Once a lesion is determined to be class III or higher, most authorities, physicians, and patients will agree that needle biopsy, performed by CT guidance, is a safe and reasonably accurate “easy” first step which can include or exclude carcinomas with 80% to 90% accuracy.^1,2

After malignancy has been established, management options, although published,^3-5 are based on experience and case studies rather than verified by trials. The major options can be summarized as surveillance, nephron-sparing surgery, and full open radical nephrectomy.

In the United States, surveillance seems difficult, particularly on the part of both patient and treating surgeon. Nonetheless, in patients with “poor performance” status (eg, elderly [older than 70 years], infirm, major comorbidity with reduced life expectancy), the literature grudgingly accepts surveillance with 6- to 12-month serial CT re-examination as reasonable and acceptable. The author is amused to find that when studies are employed to limit what we physicians do (eg, surveillance), financial costs and radiation exposure are invoked; whereas when the reverse (a more procedural strategy) is offered, such issues are not often discussed.

The use of safer, less morbid “nephron-sparing surgery,” which usually means either open or laparoscopic partial nephrectomy, is rapidly evolving into the procedure of choice, replacing traditional radical nephrectomy.³ In summary, compared with radical nephrectomy, nephron-sparing surgery is associated with similar cancer-specific mortality after the procedure and a lower likelihood of renal insufficiency and proteinuria at 10-year follow-up; however, this benefit comes at the cost of small but significant increases in complications such as operative bleeding, urine leak, and reoperation.² Thus, nephron-sparing procedures have replaced traditional radical nephrectomy in most cases of renal cancer, and choice A is incorrect.

Despite improvements in radiologic and surgical techniques in recent years, renal cancer mortality rates continue to climb (making choice C incorrect). And among patients older than 70 years, one-third die within 5 years of non-cancer causes (making choice D incorrect). This suggests that many pathologically malignant renal cancers are clinically indolent and that more defined radiologic and pathology techniques will evolve to better determine which patients will clearly benefit from entering the diagnostic/therapeutic pathways on the incidental discovery of a small renal mass.

Outcome of this case. Because the patient has type 2 diabetes, a laparoscopic partial nephrectomy was performed after a needle biopsy confirmed the presence of renal cell cancer. He is cancer-free after 3 years, but microalbuminuria has developed.

THE TAKE-HOME MESSAGE:
Incidentally discovered small renal masses (of less than 4 cm) are an increasingly common finding. CT classifications can stratify the risk of malignancy. In lesions not definitively benign, CT-guided needle biopsy is the usual initial step to make a diagnosis. If the lesion is malignant, various management options exist; partial nephrectomy is the most common.