DOI:10.2214/AJR.06.0058
AJR 2007; 188:1619-1621
© American Roentgen Ray Society
Effect of Radiofrequency Ablation of Renal Tumors on Renal Function in Patients with a Solitary Kidney
Chockeo Syvanthong1,
Geoffrey E. Wile and
Ronald J. Zagoria
1 All authors: Department of Radiology, Wake Forest University Baptist Medical
Center, Medical Center Blvd., Winston-Salem, NC 27157.
Received January 12, 2006;
accepted after revision July 31, 2006.
Address correspondence to G. E. Wile
(gwile{at}wfubmc.edu).
Abstract
OBJECTIVE. The purpose of this study was to evaluate the effect on
renal function of percutaneous radiofrequency ablation of renal tumors in
patients with a solitary kidney.
CONCLUSION. Ablation resulted in complete tumor eradication, and
there were no serious complications. Percutaneous radiofrequency ablation of
renal tumors resulted in a 16% increase in serum creatinine concentration and
a 13% decrease in creatinine clearance in patients with one kidney. These
results are comparable with those of surgical resection of tumors in this
group of patients.
Keywords: abdomen • ablation • oncologic imaging • radiofrequency • renal cell carcinoma
Introduction
In 2007, an estimated 31,590 renal tumors will be diagnosed in the United
States [1]. This large number
continues a trend that has shown a 30% increase in the past 10 years and a
100% increase since 1950 [2,
3]. This dramatic increase has
been thought to be attributed to the incidental finding of asymptomatic
lesions as the result of advances in imaging and the ability to detect small
localized tumors [1]. The
standard of care in most cases of renal cell carcinoma (RCC) has been radical
nephrectomy. However, when RCC occurs in a solitary kidney, a nephron-sparing
procedure, such as partial nephrectomy, is preferred to avoid renal failure.
The long-term oncologic effects of radical and partial nephrectomy are similar
[4]. Partial nephrectomy is
associated with considerable operating time and morbidity
[5].
Percutaneous radiofrequency ablation has been used increasingly in the
management of RCC. Percutaneous image-guided ablative procedures are being
performed on patients who are not ideal surgical candidates, including those
with one kidney [1,
2]. The purpose of this
retrospective review was to evaluate the effect of radiofrequency ablation on
serum creatinine concentration and creatinine clearance in patients with one
kidney.
Materials and Methods
Approval for the retrospective review of patient records was obtained from
the institutional review board. Retrospective review of the records of all 130
patients who had undergone radiofrequency ablation for renal tumors at our
institution yielded 12 patients with a tumor-containing solitary kidney who
underwent radiofrequency ablation between September 2003 and April 2005.
Physical examinations were performed on all patients 1 day to 1 week before
radiofrequency ablation. Serum creatinine level was measured at that
evaluation. All radiofrequency ablation procedures were performed on an
outpatient basis by one radiologist using conscious sedation and local
anesthesia. Prophylactic antibiotics were administered immediately before the
procedure. After ablation, patients stayed in an observation section of the
hospital for approximately 6 hours before release to home. Vital signs were
monitored, and a complete blood count was performed during the period of
observation. Two patients were admitted to the hospital for reasons unrelated
to radiofrequency ablation.
The diagnosis of RCC was made on the basis of biopsy, CT, or MRI findings
before ablation. Followup imaging was performed 1–3 months after
radiofrequency ablation, and these images were reviewed for evidence of
residual tumor and complications.
Technique
All patients were interviewed and examined 1 week or less before the
ablation procedure. Patients were instructed to stop taking aspirin, other
anti-platelet agents, and warfarin before radiofrequency ablation. All
radiofrequency ablation procedures were performed with a Cool-Tip system
(Radionics) under CT guidance (Fig.
1A). For radiofrequency ablation, patients were positioned prone
or decubitus on the CT table. The radiofrequency electrode selected depended
on tumor size. The active tip of the electrode was approximately 1 cm greater
than the tumor diameter. If the tumor was larger than 2 cm in diameter, a
cluster electrode was used. For tumors larger than 3 cm in diameter, multiple
overlapping ablations were used for complete tumor destruction. Ablations 8
minutes in duration were performed with the standard impedance control
algorithm included with the Radionics system. If the serum creatinine
concentration before the procedure was less than 2.0 mg/dL, contrast-enhanced
CT was performed to determine whether viable tumor remained at the end of what
was considered an adequate radiofrequency ablation session. If detected,
enhancing tumor was treated with additional ablations before the
radiofrequency ablation session was terminated.
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Fig. 1B —61-year-old woman with solitary left kidney. Axial
T2-weighted MR images without (B) and with (C) fat saturation
obtained 2 months after tumor ablation show typical appearance of a treated
tumor with low signal within ablation zone. Signal of ablated tumor
approximates signal of surrounding fat on fat-saturated image.
Contrast-enhanced images (not shown) revealed no evidence of enhancement
[2].
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Fig. 1C —61-year-old woman with solitary left kidney. Axial
T2-weighted MR images without (B) and with (C) fat saturation
obtained 2 months after tumor ablation show typical appearance of a treated
tumor with low signal within ablation zone. Signal of ablated tumor
approximates signal of surrounding fat on fat-saturated image.
Contrast-enhanced images (not shown) revealed no evidence of enhancement
[2].
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For follow-up, a clinical visit with physical examination and unenhanced
and contrast-enhanced CT or MRI (Figs.
1B and
1C) was completed 2–3
months after radiofrequency ablation. Areas of contrast enhancement (> 10 H
for CT or > 15% for MRI) were interpreted as residual viable RCC
[6].
Data Collection
Extensive chart reviews were performed on the 12 patients involved in the
study. The creatinine concentration before the radiofrequency ablation
procedure and the first concentration available at least 1 month after the
procedure were recorded for each patient. We also recorded the patient's
weight to calculate creatinine clearance, adjusting for weight and age, as a
more complete means of assessing renal function. Complications during or after
the procedure also were recorded.
Results
The study group consisted of 12 patients (four women, eight men; mean age,
77 years; age range, 61–87 years). Before the radiofrequency ablation
procedure, all patients had an average serum creatinine (Cr) concentration of
2.28 mg/dL (range, 0.9–5.5 mg/dL). The average follow-up time was 2.9
months (range, 1–6 months), at which time an average creatinine
concentration of 2.65 mg/dL was recorded (range, 0.9–6.9 mg/dL)
(Fig. 2). The follow-up
creatinine concentration indicated an average 0.37 mg/dL increase, which
represents a 16.48% increase from baseline for this study group. The average
creatinine clearance before the procedure was 40.83 mL/min (range, 8–69
mL/min). At follow-up visits 1 month or more after the procedure, the average
creatinine clearance was 35.42 mL/min (range, 7–69 mL/min), which
represents a 13.25% decrease in estimated creatinine clearance for men,
calculated as [(140 – age) x weight] / (72 x Cr), and women,
calculated as 0.85 [(140 – age) x weight] / (72 x Cr).
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Fig. 2 —Creatinine clearance after radiofrequency ablation. Graph
shows long-term follow-up results for 12 patients. Because of variable
follow-up periods for this group, data analysis was performed on findings at
1-month follow-up visit.
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Among the 12 patients in this study, a range of one to four tumors were
ablated during each treatment session. One patient had two tumors, one patient
had four tumors, and the others had one tumor. The patient with four lesions
ablated had a serum creatinine concentration of 1.7 mg/dL before ablation and
a follow-up concentration of 1.8 mg/dL, which corresponds to estimated
creatinine clearances of 22 and 21 mL/min, respectively. The patient with two
tumors ablated had a serum creatinine concentration of 1.2 mg/dL before
ablation and a follow-up creatinine concentration of 1.6 mg/dL, which
corresponds to estimated creatinine clearances of 65 and 49 mL/min,
respectively. Eleven of the 12 patients in this study were treated with
curative intent. The 12th patient had stage IV RCC with widespread metastasis
and intractable hematuria. This patient underwent radiofrequency ablation for
control of hematuria, which completely resolved after radiofrequency ablation.
Biopsies performed before radiofrequency ablation revealed RCC in nine
patients and oncocytic neoplasm in one patient. The diagnosis of RCC was based
on imaging findings alone in the other two patients. The size of the tumors
ranged from 1 to 4.4 cm in largest diameter.
None of the 12 patients had complications during the radiofrequency
ablation procedure. Procedures were performed on an outpatient basis in 10 of
12 cases. One patient remained hospitalized for 4 days after the procedure to
reestablish therapeutic warfarin levels. Another patient stayed in the
hospital 5 days after the procedure while receiving antibiotics for bacteremia
and bacteruria found before the procedure. This patient needed radiofrequency
ablation for the management of persistent hematuria after failed urologic
interventions.
The success of radiofrequency ablation was measured with follow-up
contrast-enhanced CT or MRI 2–3 months after radiofrequency ablation.
Within this time interval, none of the patients had evidence of recurrent or
residual tumor at the radiofrequency ablation site.
Discussion
Although radical nephrectomy is the standard of care of many patients with
RCC, nephron-sparing treatment is used whenever possible to treat patients
with RCC in a solitary kidney. Partial nephrectomy is the standard of care
with respect to nephron-sparing procedures. Duque et al.
[7] found that 4–8 weeks
after partial excision of a solitary kidney for RCC, nine of 10 patients had a
greater than 0.6 mg/dL increase in serum creatinine concentration. The tenth
patient recovered fully. In a study by Adkins et al.
[8] that included 30 patients,
the median serum creatinine concentration increased from 1.5 to 1.8 mg/dL.
Gill et al. [9] evaluated
laparoscopic partial nephrectomy of a single tumor in the solitary kidneys of
22 patients. Those investigators found median serum creatinine concentration
increased from 1.1 to 1.5 mg/dL in a median follow-up period of 7.1 months,
representing a median increase of 33%. Our results showed the average serum
creatinine concentration increased 0.37 mg/dL after radiofrequency ablation.
This finding is similar to the increase of 0.3 mg/dL in the study by Adkins et
al. and is better than the increase of 0.6 mg/dL found by Duque et al.
The average follow-up periods in the studies by other authors
[7–9]
were longer than those in our study. The data in a study by Saranchuk et al.
[10], however, show that the
serum creatinine concentration in their sample increased to its greatest value
1 month after partial excision of a solitary kidney and continued to decline
to nearly normal levels over the course of the next year. It would be
reasonable to suggest that the length of our study was sufficient to show
major deficiencies in renal function, if they were to occur in the absence of
other confounding variables.
With estimated creatinine clearance as a measure of renal function, our
sample had an average decrease of 5.41 mL/min, which represents a decrease of
13.25%. In comparing percentage loss of renal function, although serum
creatinine concentration increased 16.48%, the decrease in estimated
creatinine clearance was smaller. Creatinine clearance accounts for body
habitus and may be a more accurate measurement of true renal function than is
serum creatinine concentration.
In summary, patients with one kidney who undergo radiofrequency ablation of
a renal tumor can be expected to have a decrease in renal function of
13–16%. This value is similar to that expected after partial
nephrectomy, which is a more invasive procedure with higher morbidity and
longer hospitalization. Percutaneous radiofrequency ablation appears to be an
effective alternative to partial nephrectomy in this subgroup of patients. No
major complications occurred in this study group, and short-term follow-up
indicated good oncologic control.
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Abstract
Introduction
