Focal hydrothermal ablation: preliminary investigation of a new concept.

Purpose: To determine whether focal tissue ablation is possible with interstitial instillation of steam.

Methods: Fresh swine livers were used. Through a 20 gauge needle, steam was instilled every 5 s, 3 (n = 5), 6 (n = 5), 9 (n = 5), or 12 (n = 5 + 5) times in a liver lobe. The ablated zones were sectioned parallel (n = 20) or perpendicular (n = 5) to the needle track. The longitudinal long and short axis diameters, or transverse long and short axis diameters of areas with discoloration on macroscopic examination, were measured. The experiment was repeated in vivo on a pig. Steam instillation was performed once every 5 s for 5 min in the liver (n = 3) and in muscle (n = 4), and temperature changes at three neighboring sites were monitored. Long and short axis diameters of the discolored areas were measured.

Results: A well-defined area of discoloration was invariably present at the site of steam instillation. The median longitudinal long axis diameter were 2.0, 2.5, 2.5, and 3.5 cm for 3, 6, 9, and 12 steam instillations in vitro, while median short axis diameters were 1.0, 1.5, 1.5, and 1.5 cm, respectively. Six attempts at ablation in vivo could be successfully completed. The long axis diameters of the ablated zones in the liver were 7.0 and 8.0 cm, while in muscle it ranged from 5.5 to 7.0 cm.

Conclusion: Instillation of steam in the liver in vitro and in vivo, and in muscle in vivo rapidly leads to circumscribed zones of coagulation necrosis.