Risk Factors For Renal Function Impairment Following Radiofrequency Ablation Of Renal Tumors

Purpose To evaluate the various factors that affect renal function following percutaneous radio-frequency ablation (RFA) therapy in patients with renal tumors. Materials and Methods Between 2010 and 2018, 91 patients diagnosed with renal tumors using ultrasonography and CT-guided RFA were enrolled. We retrospectively investigated the serum creatinine (SCr) level and estimated glomerular filtration rates immediately before RFA and during post-treatment follow-up. The patients were divided into two groups based on the degree of change in SCr level (0.3 mg/dL). Group comparisons were performed using univariable and multivariable logistic regression analyses to determine the factors impacting renal function. Results Impaired renal function was associated with solitary kidney, chronic kidney disease (CKD) over stage 3, and pyeloureteral injury. Sex, age, other cancers, tumor size, location, growth pattern, and proximity to the collecting system were not significantly associated with impaired renal function. There was a difference in the overall change over time between the association with and without solitary kidney, CKD stage 3, and pyeloureteral injury. Conclusion Among the medical conditions present before RFA, solitary kidney, and CKD over stage 3 could be considered risk factors for impaired renal function. Post-procedural pyeloureteral injury can also be considered a risk factor. 

Index terms Radiofrequency Ablation; Kidney Neoplasms; Kidney Function Tests

ORGANIC HERBS TO PROTECT KIDNEY FUNCTION

INTRODUCTION 

Radical nephrectomy used to be considered as the choice of treatment for patients with renal cancer (1). In cases of small renal cancer, solitary kidney, or bilateral renal cancer, partial nephrectomy has been shown to have comparable oncologic outcomes to that of an alternative treatment (1, 2). The nephron-preserving surgery can also be expected to prevent the overtreatment of radical nephrectomy in benign lesions (3). However, nephron- preserving surgery may significantly contribute to morbidity and mortality in patients with major comorbidities. Primarily, renal function impairment is a troublesome sequela of renal cancer surgery, since the developing or aggravating chronic kidney disease (CKD) increases the risk of mortality, hospital stay, and risk of cardiovascular disorders (4, 5). The American Urological Association considers percutaneous radiofrequency ablation (RFA) as an alternative to surgery for poor surgical candidates with comorbidities (6). 

Many studies show that RFA has minimal influence on renal function (7-11). In the case of renal function loss following RFA, tumor predictors affecting renal function may be closely related to lesion size, location, number, and successful ablation rate (12). Apart from tumor predictors, the factors influencing renal function have not been elucidated. It is important to understand the risk factors for renal function impairment following RFA to aid patient management and guidance. The purpose of the present study is to evaluate various factors that affect renal function after RFA therapy in patients with renal tumors.

MATERIALS AND METHODS

This retrospective study was approved by our Institutional Review Board. Informed consent of patients was waived (IRB No. DAUHIRB-21-165).PATIENTS Between January 2010 and December 2018, 112 patients with renal tumors were treated using ultrasonography (US) and CT-guided RFA. The inclusion criteria comprised the presence of renal masses upon imaging for renal cell carcinoma (RCC) or sporadic Bosniak III or IV lesions on kidney CT or MRI, and at least 1 year of imaging and renal function test follow-up after RFA. Twenty-one patients were excluded due to follow-up loss (n = 14), presence of a large renal tumor (8.8 cm, n = 1), renal metastases from lung cancer (n = 1) and bladder cancer (n = 1), RCC arising from a transplanted kidney (n = 1), bilateral multiple RCCs in a patient with von-Hippel-Lindau disease (n = 1), and subsequent nephrectomy for recurrence (n = 2).

Tables 1 and 2 show clinical and radiological data. A total of 91 patients (60 male and 31 female; mean age, 55.5 years; age range, 26–85 years; mean follow-up period, 66 months; follow-up range, 12–121 months) with 91 renal tumors were finally included in this study. All patients with CKD (7 of 91) were at stage 3. All patients with solitary kidney (9 of 91) underwent a previous radical nephrectomy due to RCC. 

Renal tumor size was measured on contrast-enhanced kidney CT or MRI, and the median tumor size was 1.7 cm (range, 0.8–5.6 cm). Measurement of the longest diameter in the axial or coronal plane was selected as the tumor size. Tumor radiologic features were categorized based on the tumor classification algorithms suggested by the Radius, Exophytic/Endophytic properties, Nearness of the tumor, Anterior/posterior, and Location relative to polar lines (R.E.N.A.L) nephelometry score (13). Renal tumors were classified as exophytic or endophytic according to the lesion location. Exophytic tumors were classified based on the extent to which the tumor bulged out from the kidney surface (≥ 50% or < 50%). Entirely endophytic tumors were considered as enclosed renal masses by uninvolved normal renal parenchyma (13).

Various criteria have been used to define a significant worsening of renal function. Renal function results were categorized into continuous [serum creatinine (SCr) or estimated glomerular filtration rates (eGFRs) change] and categorical (CKD stages ≥ 3, ≥ 3b, ≥ 4, and end-stage renal disease) outcomes (14-23). The Acute Kidney Injury Network's working group proposed an absolute increase in the SCr level of at least 0.3 mg/dL as the diagnostic criteria for stage 1 of acute kidney injury (24). Although the patient group in this study included those with acute and chronic renal injury, the definition of renal functional impairment after 

RFA has not been specifically established. We defined an SCr level change of at least 0.3 mg/ dL between pre-RFA and post-RFA as a significant change, indicative of renal function inpairs. The patients were divided into two groups based on the degree of change in the SCr level. The 15 patients who presented an increase in SCr level of more than 0.3 mg/dL, three times consecutively in a year, compared with pre-RFA SCr level, constituted group A. The other 76 patients with an SCr level change of less than 0.3 mg/dL constituted group B.

RFA PROCEDURE 

RFA was conducted by a neuroradiologist with 14 years of experience in percutaneous US and CT-guided ablation in the kidney. CT-guided RFA was performed using a CT scanner (Sensation, Siemens Medical Solutions Inc., Malvern, PA, USA). All cases were performed with a single (with one 2.0–3.0 cm tip) internally cooled radio-freequency electrode (Radionics, Burlington, MA, USA) with the impedance-modulated pulsed current. The patients lay in a modified lateral position on the CT table based on the tumor location. US and CT-guided RFA procedures are composed of planning, targeting, monitoring, controlling, and assessment of treatment response (25). US or CT was performed to measure the angle and depth of the electrode insertion. While checking the location of the renal tumor under the US, an electrode was inserted into the boundary of the tumor. Subsequently, a CT was performed to confirm whether the electrode was placed within the tumor. Following this, RFA was performed using the electrode for 12 minutes. When residual tumors were found on an additional CT, the position of the electrode was adjusted with the help of the CT and an additional procedure was performed for 6–12 minutes (26, 27). When renal tumor ablation of 0.5 cm or more of the tumor margin was considered appropriate by the neuroradiologist, the RFA session was completed (12).

DATA ANALYSIS 

Contrast-enhanced multiphasic CT imaging was performed immediately after the procedure to serve as a basis for comparison of follow-up images. The purpose of 1-day follow-up CT was to check for immediate complications. Patients were followed up with contrast-enhanced CT or dynamic contrast-enhanced MRI at 1 day, 1 month, 3 months, and 6 months and were then followed up twice a year. RFA sessions, residual tumor, technical efficacy, and local tumor progression were recorded based on the International Working Group of Image-Guided Tumor Ablation (IWG-IGT) criteria. The residual tumor was considered to have a focal enhancing lesion observed on the first follow-up CT scan 1 month after RFA. Technical efficacy was defined as no focal enhancing lesion on images taken at the first follow-up. Local tumor progression was defined as a focal enhancing lesion on images taken at the second follow-up or increased size of ablation zone or suspicious findings in MR images (decreased T1 signal intensity, increased T2 signal intensity, or increased diffusion-weighted signal with decreased apparent diffusion coefficient) (25). After the procedure, periodic SCr levels and eGFRs were recorded for the previous day and post RFA (1 day, 3 days, 1 week, 1 month, and 6 months, followed by twice a year) to confirm renal function impairment. eGFRs were estimated using the diet modification in the renal disease equation (28). Time points for follow-up periods in previous studies vary. In this study, renal function outcomes within a year were used to prevent the inclusion of other competitive factors of renal function deterioration and to check the long-term renal function changes rather than acute kidney injury (22). 

Post-procedural complication types (major or minor) were recorded based on the IWG-IGT criteria (25). A major complication is defined as one that may result in significant morbidity (e.g., unexpected organ loss or permanent adverse sequelae) requiring pharmacological, radiological, or surgical treatment. It can increase the level of care required, result in hospital admission, or substantially lengthen the hospital stay. All complications other than the major ones are considered minor complications requiring supportive care.