PATIENTS AND METHODS
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- PATIENTS AND METHODS
We reviewed the medical records of 14 patients with solitary kidneys and solid renal masses of ≤ 5 cm who underwent percutaneous cryoablation. Two patients were excluded from the analysis as they were lost to follow-up and thus 12 patients underwent cryoablation (10 men and two women, mean age 62.5 years, range 29–76). All patients had radiographically documented solid renal masses by either CT or MRI. The percutaneous cryoablation procedure used was described in detail previously and is only briefly presented here . All patients underwent a standard preoperative evaluation consisting of a chest X-ray, electrocardiogram, complete blood count, and analysis of serum blood urea nitrogen, creatinine, electrolytes and alkaline phosphatase. Patients were given general endotracheal anaesthesia and placed into an open 0.5 T MRI unit (General Electric Medical System, Milwaukee, WI, USA). Gradient imaging was used to locate the mass and one to four 3-mm cryoprobes placed percutaneously into the mass. The location of the probe in the tumour was confirmed with sagittal and transverse planar images. An argon-based cryosystem (Galil Medical, Tel Aviv, Israel) was used to create an ice-ball at − 120 °C at the probe tip. The ice-ball was then melted and two additional freeze-thaw cycles applied. The patients were admitted for 23-h observation and subsequently followed up at 1 week, 1, 3 and 6 months and every 6 months thereafter. A physical examination and analysis of blood urea nitrogen, creatinine, and urine were conducted at each visit. Radiographic imaging of the kidney was obtained by either CT or MRI at each follow-up, beginning with the 1-month visit.
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- PATIENTS AND METHODS
Ten patients had undergone a previous nephrectomy for RCC and in the remaining two, one had had a nephrectomy secondary to trauma and the other a congenital horseshoe kidney. Table 1 presents the characteristics and treatment results for these patients. Two of the patients who had a previous radical nephrectomy had stable metastatic disease at the time of cryoablation. All procedures caused minimal morbidity and there were no deaths. Eight of the 12 patients had total ablation of the tumour after one treatment; of the four with residual tumour, three underwent repeat cryoablation, two of whom had total ablation after the second treatment. Overall, two of the 12 patients did not have complete tumour ablation. Treatment success was defined as a lack of contrast enhancement in the treated area on follow-up CT or MRI. To date, no patient has developed new metastatic disease.
Table 1. Patient characteristics and treatment results
|Age, years|| 76|| 62|| 29|| 64|| 70|| 65|| 66|| 37|| 49|| 47|| 72|| 66|
|Previous nephrectomy for malignancy||Yes||Yes||No||Yes||Yes||Yes||Yes||Yes||No||Yes||Yes||Yes|
|Tumour size, cm|| 4.0|| 3.8|| 1.4|| 1.3|| 3.5|| 4.7|| 1.0|| 2.0|| 4.5|| 2.9|| 1.5|| 2.5|
|No. of probes|| 1|| 1|| 1|| 1|| 2|| 4|| 2|| 3|| 3|| 3|| 2|| 2|
|No. of treatments|| 1|| 2|| 1|| 1|| 2|| 1|| 1|| 1|| 2|| 1|| 1|| 1|
|Blood urea nitrogen, µg/L|
|Before||240||300||180||240||130||210|| – || – ||80||180||340||430|
|After‡||250||300||120|| – ||120||210||1240||120||70|| – ||250||360|
|Before|| 20|| 17|| 4|| 14|| 16|| 16|| 36†|| 20|| 11|| 15|| 18|| 26|
|After‡|| 19|| 22|| 5|| 17|| 16|| 17|| 48|| 12|| 10|| – || 17|| 23|
|Follow-up, months|| 36|| 30|| 12|| 24|| 24|| 18|| 12|| 12|| 3|| – || 18|| 6|
Patient no. 3, a 29-year-old woman with a congenital horseshoe kidney, had several comorbidities and was not considered to be a surgical candidate. She was offered the option of cryoablation and agreed to proceed.
Table 1 also presents the blood urea nitrogen and creatinine levels of the patients. In the immediate follow-up visit at 1 week no patient had a significant increase in serum creatinine. Patient no. 7 was diagnosed with RCC of a transplanted kidney, which was treated successfully, but the patient had an increase in creatinine secondary to chronic rejection. Patient no. 10 was referred from an outside urologist and no follow-up information was available for renal function. CT at 6 months after cryoablation showed no enhancement of the renal mass. Two patients had gross haematuria that resolved within 24 h. The mean (range) follow-up was 16.3 (3–30) months, with all patients alive. Six patients had no tumour visible on the last imaging study; four had no contrast enhancement and a decrease in the size of the mass of 20–50%. Of the two failures, one had a 0.5-cm enhancing residual mass at the 22-month follow-up and selected observation. The second patient had two large tumours, each of 4.5 cm, after ablation. Half of the patients had a stable or improved serum creatinine in follow-up; in five the creatinine increased by 1–12 µg/L and no follow-up data for renal function were available for one patient.
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- PATIENTS AND METHODS
The minimally invasive treatment of small renal tumours has been successful within a short-term follow-up [1–4]. While the results of partial nephrectomy for tumours in solitary kidneys has been excellent, the question arises as to whether a minimally invasive treatment such as cryoablation could achieve similar results with less morbidity. In the present patients cryoablation caused minimal morbidity and, more importantly, preserved renal function. While the follow-up was short it is encouraging that renal function remained stable or only decreased slightly.
In four of the 12 patients the ablation was incomplete after one treatment; early in the study one patient was treated with only one cryoprobe, which probably accounted for the incomplete ablation. The second patient had two parenchymal tumours of 4.5 cm diameter that were too large to ablate successfully. This patient refused nephrectomy and therefore the only treatment option available was cryoablation. Two of the patients had complete tumour ablation after two treatments. These tumours were parenchymal and may have had large-calibre blood vessels close to the tumour. In this situation the rapid blood flow prevents the ice-ball from cooling the tumour tissue to the lethal range. After a period, with most of the tumour destroyed, re-treatment of the residual tumour becomes easier as the cryoprobe can be placed directly in this area.
The excellent results with partial nephrectomy in solitary kidneys have been well documented. Smith et al. reported their results in 17 patients with stage I disease, with a mean survival of 52 months. Novick et al. described the results for long-term renal function after a partial nephrectomy in patients with a solitary kidney, finding that it remained stable in 12 patients at a mean follow-up of 7 years.
For local tumour recurrence, various investigators have reported incidences of 0–11%[7,8]; in the report by Hafez et al. on 327 patients, the local recurrence rate was zero for stage T1 and only 2% for stage T2 disease. Only three patients with T1 disease developed metastatic disease at a mean of 44.8 months. Clearly, patients with low-volume disease have a very small chance of developing local recurrence or metastatic disease.
Campbell et al. reported a complication rate of 30% for partial nephrectomy in 259 patients. The most common complication was urinary fistula formation in 44 patients, followed by acute renal failure in 33. Significantly, acute renal failure was the most common complication among patients with a solitary kidney. Predisposing factors for these patients included a tumour of > 7 cm, more than half the parenchyma excised, and prolonged ischaemia time. In 28 of 33 patients with acute renal failure it eventually resolved. To date there have been no reports of urinary fistula formation or renal failure after renal cryoablation. As it is necessary to clamp the renal artery during a partial nephrectomy, this occasionally leads to a temporary or permanent decrease in renal function. As the renal artery is open during cryoablation, there is less chance of a decrease in renal function after treatment.
The success of cryoablation is limited by tumour size and/or location; tumour next to or involving the collecting system cannot be treated with cryoablation because of the possibility of either incomplete tumour destruction or injury to the pelvicalyceal system. In trying to avoid injury to the collecting system, a small rim of tumour may be inadequately ablated, as noted in some patients who were treated with tumours close to the collecting system. Because of this we no longer attempt to treat tumours that do not have a 5–7 mm margin from the renal pelvis or calyces.
One to four probes were used in the present study; when the procedure was initially developed one probe was used and repositioned during treatment to ensure that the entire tumour was treated. After gaining more experience with animal studies it was realized that placing several probes would allow the rapid creation of the ice-ball, decreasing the overall procedure time.
Our experience with renal cryoablation shows a low incidence of complications (6%, unpublished data); in the present series of patients with solitary kidneys there were no complications associated with the procedure. The tumour was totally ablated by the initial treatment in three-quarters of the patients. While this success rate is lower than that for partial nephrectomy, we expect this to improve as experience is gained in selecting patients and in treatment techniques. Continued monitoring will be required for a longer follow-up to ensure the durability of these results. None of the patients to date have had local recurrence detected on imaging studies, although the mean follow-up is only 16 months.
In conclusion, cryoablation of renal tumours in patients with solitary kidneys is successful, with minimal morbidity and little change in renal function. A long-term follow-up will be required to confirm these results. However, cryoablation might be a treatment option in patients with solitary kidneys.