Background and Purpose: Many ablative techniques have been described for treatment of small renal tumors. We investigated interstitial laser ablation (ILA) of porcine kidneys with a new-generation diffuser tip fiber. Materials and Methods: Six female farm pigs underwent bilateral lower-pole ILA of normal kidneys via a midline approach. The acute group consisted of three pigs that underwent immediate post-treatment bilateral nephrectomy, while the chronic group survived for 45 days prior to bilateral nephrectomy. The lower pole of each kidney was treated with a diode laser in temperature-adaptive mode (100°C) with the diffuser tip fiber. The treatment time was increased for each pig in each group, from 4 minutes to 8 minutes to 12 minutes. Results: The acute lesions were elliptical, with the depth being longer than the width. The dimensions of the acute lesions on gross inspection were 18 x 9 and 17 x 9 mm in the 4-minute treatment pig, 25 x 6 and 18 x 15 mm in the 8-minute treatment pig, and 22 x 18 and 19 x 12-mm in the 12-minute treatment pig. Reduced nicotinamide adenine dinucleotide staining of the acute lesions revealed a nonviable zone of 14 x 18 and 15 x 10 mm in the 4-minute treatment pig, 16 x 8 and 12 x 7 mm in the 8-minute treatment pig, and 11 x 7 and 14 x 9 mm in the 12-minute treatment pig. Histologic architecture was preserved. Gross examination of the chronic kidney revealed a divot with a scar in the treatment area. Histologic examination showed an irregularly shaped area of fibrosis and loss of normal architecture, with the lesions being smaller than those seen on the acute sections. Conclusions: Interstitial laser ablation of the kidney with a diffuser tip fiber produces adequate cell death but small lesions. Further studies with multiple fibers or active monitoring and repositioning of the fiber to produce larger lesions are necessary.
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