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Abstract and Introduction
Abstract
Objective: Percutaneous thermal ablation is an emerging technique in the management of renal cell carcinoma (RCC), with greatest efficacy in tumors ≤ 3 cm. The purpose of this retrospective study was to evaluate the role and utility of pretreatment CT-guided biopsy in patients referred for percutaneous thermal ablation of renal tumors.
Conclusion: Less than 5% of samples in our study were benign, and 11.8% were nondiagnostic. Biopsy in smaller lesions was less accurate; therefore biopsy is less useful for these renal lesions. Because fine-needle aspiration (FNA) has higher sensitivity than core biopsy, an appropriate algorithm may be to begin with FNA and reserve core biopsy for cases in which an onsite cytotechnologist is unavailable or deems the sample of inadequate cellularity.
Introduction
Advanced diagnostic imaging in the routine medical evaluation of patients has led to the increased incidental diagnosis of potentially malignant renal masses.[1] Currently, there are several treatment options for these suspicious renal masses including open radical nephrectomy, laparoscopic radical nephrectomy, and nephron-sparing techniques such as open or laparoscopic partial nephrectomy and observation.[2-5] Minimally invasive therapies including percutaneous thermal ablation are gaining wider acceptance in the management of these lesions.[6]
With percutaneous ablative techniques, current practice involves a preprocedure imaging-guided biopsy to render a specific histopathologic diagnosis.[6-8] Reasons for obtaining a biopsy before ablation include lesions treated by ablation are often ≤ 3 cm, a group of masses in which the imaging diagnosis is less specific,[9] the need to determine appropriate follow-up, avoidance of treatment for benign lesions, and determining the efficacy of percutaneous ablative techniques as emerging technologies.[7,10] The development of better histologic techniques has increased the specificity of a tissue diagnosis.[11] The purpose of this study was to use retrospective data to evaluate the role and utility of pretreatment CT-guided biopsy in patients referred for percutaneous thermal ablation of renal tumors diagnosed as renal cell carcinoma (RCC) by imaging at our institution. The data may then influence future decisions whether biopsy is necessary to determine optimal treatment algorithms in the setting of suspected RCC and to further evaluate the diagnostic specificity of imaging interpreted as "high probability" for RCC Materials and Methods
With institutional review board approval, we retrospectively reviewed the radiologic and pathologic records for all consecutive kidney ablation treatments performed at our institution from 2001 to 2005. Patients were referred for treatment based on imaging findings and clinical history; patient selection criteria have been described previously.[12] Data were included in the analysis if the pretreatment evaluation included CT or MRI, if the biopsy was performed during the same session as the ablation, and if the lesion being treated had not previously been biopsied or treated. All masses characterized by imaging in this study were found to enhance greater than 20 H on contrast-enhanced CT, were found to enhance greater than 15% on MRI with gadolinium, or were classified as Bosniak III or IV cystic masses.[13] There was no pretreatment evidence of direct tumor extension beyond the kidney.
Over the observational period, 106 lesions were treated in 103 patients. Of the three patients who underwent multiple treatments, two were treated for multiple lesions, one with a history of von Hippel-Lindau disease and one with multifocal RCC. One treatment was for a recurrence at the site of the original ablation. Thirteen lesions were excluded from analysis, six because the biopsy was performed in a separate session and the results were known before the radiofrequency ablation, five because a biopsy was not performed at all, one because the biopsy and treatment were directed at an area of recurrence in a prior radiofrequency ablation treatment bed, and one because it was characterized solely by sonography. The study cohort therefore is made up of 93 lesions in 91 patients.
Table 1 summarizes the imaging workup of the 93 lesions. A total of 125 imaging studies were performed. Most lesions were characterized by CT, which was performed before and after injection of IV contrast material whenever possible, as determined by the patient's renal function, age, and comorbidities. Almost half of the patients underwent MRI, and 32 patients were imaged with both techniques. The average lesion diameter was 2.9 cm, with a range from 0.7 to 7.8 cm. Two thirds of the lesions were ≤ 3 cm, with 3.2% (3/93) measuring ≤ 1 cm, 34.4% (32/93), 1-2 cm, and 31.2% (29/93), 2-3 cm.
Tissue was obtained using CT guidance through a 19-gauge needle using a coaxial system (Truguide coaxial biopsy needle, C.R. Bard) with a minimum of two 22-gauge fine-needle aspiration (FNA) biopsies (Chiba biopsy needle, Cook Medical) and a minimum of two 20-gauge core biopsies with an automated biopsy gun (Bard Monopty biopsy instrument, C.R. Bard) immediately before the ablation in 93 cases. For the purposes of this study, the samples described as FNA were those obtained with 22-gauge needles and that underwent a cytologic examination, whereas those categorized as core biopsy samples were obtained with the 20-gauge automated core biopsy gun and were evaluated histologically. The number of samples obtained for both cytologic and histologic evaluation sometimes exceeded these minimums and varied from patient to patient at the discretion of the radiologist performing the procedure. These actual numbers were not systematically recorded in the procedural notes. Figure 1 shows an image from a biopsy procedure. A cytotechnologist was present during the procedure to assess the specimen intended for cytologic examination for adequate cellularity. The samples were then sent to pathology where the same pathologist performed the cytologic and histologic evaluation for each sample. Samples were treated routinely with H and E, and, at the discretion of the interpreting pathologist, additional immunohistochemical studies were performed.
Figure 1. (cli
ck image to zoom)
84-year-old man with exophytic 3.8-cm solid mass in upper pole of left kidney, prone position. Axial unenhanced CT image shows 19-gauge outer needle is in place, and coaxial technique is used to obtain multiple fine-needle aspiration samples using 22-gauge biopsy needles.
Biopsy results were initially classified as nondiagnostic or diagnostic. All biopsy specimens that yielded only benign renal parenchymal cells, necrosis, inflammation, or scant cellular tissue were classified as nondiagnostic. Results classified as diagnostic included RCC, oncocytic neoplasm not otherwise specified (NOS), highly suspicious for RCC, suspicious for RCC, or benign if a specific benign cause such as angiomyolipoma (AML) or oncocytoma was identified on either the FNA or the core biopsy. We asked a pathologist with expertise in urinary tract neoplasms to review all the cases listed as oncocytic neoplasm NOS, highly suspicious, suspicious, nondiagnostic, and benign in an attempt to refine or confirm the diagnosis.
After this review, the diagnostic lesions were further subdivided into benign or malignant categories. Benign lesions included both AMLs and lesions confidently characterized as oncocytoma on the basis of histochemical, immunocytochemical, and ultrastructural studies.[11,14-16] Malignant lesions included all lesions definitively characterized as RCC. The lesions described in the final pathology report as highly suspicious for RCC or suspicious for RCC were included in the malignant category because the samples contained cells with malignant features but were limited by a low number of collected malignant cells. Also, results described as oncocytic neoplasm NOS that could not be diagnosed as a benign oncocytoma were included in the malignant category after the second review.
Sensitivities of the FNA samples and of the core biopsy samples were calculated using the subset of diagnostic samples in which both an FNA and a core biopsy specimen were obtained. True-positive results were defined as those in which a diagnosis of malignancy was made from a biopsy sample. False-negative results were defined as those biopsies in which a diagnosis of malignancy was made on the alternative mode of biopsy (i.e., FNA was nondiagnostic and core biopsy was diagnostic for RCC). The false-positive rate for the biopsy was defined as zero. Specificities could not be calculated because cases with true-negative results were neither sampled nor treated. These data were also used to calculate the positive predictive value of the pretreatment imaging workup to which each lesion was subjected.
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