IMAGING

Imaging-guided radiofrequency ablation of solid renal tumors
Farrell MA (1), Charboneau WJ (1), DiMarco DS (2), Chow GK (2), Zincke H (2), Callstrom MR (1), Lewis BD (1), Lee RA (1), Reading CC (1)
(1) From Department of Radiology, Mayo Clinic, 200 First St., Rochester, MN 55902, and (2) Department of Urology, Mayo Clinic, Rochester, MN 55902.
AJR Am J Roent. 2003; 180: 1509-13

• Purpose: We performed a retrospective review of imaging-guided radiofrequency ablation of solid renal tumors.
• Materials and Methods: Since May 2000, 35 tumors in 20 patients have been treated with radiofrequency ablation. The size range of treated tumors was 0.9 - 3.6 cm (mean, 1.7 cm). Reasons for patient referrals were a prior partial or total nephrectomy (nine patients), a comorbidity excluding nephrectomy or partial nephrectomy (10 patients), or a treatment alterative to nephron-sparing surgery (one patient who refused surgery). Tumors were classified as exophytic, intraparenchymal, or central. Sixteen patients had 31 lesions that showed serial growth on CT or MR imaging. Of these 16 patients, four patients with 10 lesions had a history of renal cell carcinoma, and two patients with 11 lesions had a history of von Hippel-Lindau disease. Four patients had incidental solid masses, two of which were biopsied and shown to represent renal cell carcinoma, and the remaining two masses were presumed malignant on the basis of imaging features. Successful ablation was regarded as any lesion showing less than 10 H of contrast enhancement on CT or no qualitative evidence of enhancement after IV gadolinium contrast-enhanced MR imaging.
• Results: Of the 35 tumors, 22 were exophytic and 13 were intraparenchymal. Twenty-seven of the 35 were treated percutaneously using either sonography (n = 22) or CT (n = 5). Two patients had eight tumors treated intraoperatively using sonography. Patients were followed up with contrast-enhanced CT (n = 18), MR imaging (n = 5), or both (n = 5) with a follow-up range of 1 - 23 months (mean, 9 months). No residual or recurrent tumor and no major side effects were seen.
• Conclusion: Preliminary results with radiofrequency ablation of exophytic and intraparenchymal renal tumors are promising. Radiofrequency ablation is not associated with significant side effects. Further follow-up is necessary to determine the long-term efficacy of radiofrequency ablation.
  
• Editorial Comment
  Cryotherapy has been the most frequently thermal ablative technique used for alternative treatment of localized renal cell carcinoma. There are only few reports describing the utilization of radiofrequency ablation (RF) to renal tumors including only small series of patients. Radiofrequency renal tumor ablations can be performed under sonography or computed-tomography-guided percutaneous approach. After treatment, patients are usually followed up with CT scans at 6 weeks and 3, 6, and 12 months, and every 6 months thereafter. Successful ablation has been considered by many authors as a lesion along with a margin of normal parenchyma that no longer enhanced (less than 10 Hounsfield units) on follow-up contrast studies. The point of this report is that 35 tumors, ranging in size from 0.9 to 3.6 cm (mean = 1.7 cm), were treated by RF with no residual or recurrent lesions. The criterion of successful ablation was the same used by other authors and based strictly on radiolologic findings (absence of lesion’s enhancement). Radiographic follow-up of radiofrequency ablated small renal tumors, however, may demonstrate little or no residual contrast enhancement depending on tumor size, location within the kidney, and mode of delivering radiofrequency energy. As already pointed out by the authors the absence of postprocedural biopsy can be considered a relative limitation of this study since pathologic examination after RF ablation may show a residual viable tumor in few patients. Another point to be considered is that when performed, adequate histopathologic evaluation of the tumors specimens treated by RF-ablations should include hematoxylin-eosin and a nicotinamide adenine dinucleotide staining in order to determine the presence or absence of tissue viability. This manuscript is recommended because shows very clearly that RF ablation can successfully destroy small peripheral renal tumors with no significant damage to the normal renal parenchyma and more important without significant side effects.

Dr. Adilson Prando
Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil