Effect of freeze time during renal cryoablation: a swine model

Cryotherapy provides a minimally invasive treatment for small renal tumors via an open, percutaneous, or laparoscopic approach. We sought to determine the most appropriate duration of freezing and the number of probes necessary to produce cell death without concomitant morbidity.

Nine domestic female pigs were divided into three groups of three animals each. Each group underwent a single freeze cycle with a commercially available cryotherapy device with 3.4-mm probes: group 1 for 5 minutes, group 2 for 10 minutes, and group 3 for 15 minutes. The right kidney was treated with a single probe, the left with a double probe. Animals were permitted to survive for an average of 4.8 days (range 4-7 days), after which the kidneys were harvested. A single pathologist examined the kidneys for gross and histologic changes. Evidence of complications (fistula, bleeding, bowel injury) was documented at the time of necropsy.

For group 1, the temperature obtained with a single probe 5, 10, 15, and 20 mm from the probe was -57 degrees C, 3 degrees C, 25 degrees C, and 33 degrees C, respectively; for group 2 -85 degrees C, -37 degrees C, -2 degrees C, and 25 degrees C; and for group 3 -10 degrees C, -45 degrees C, -20 degrees C, and 6 degrees C. For group 1, the temperature obtained with a double probe at 5, 10, 15, and 20 mm from each probe was -65 degrees C, 0 degrees C, 20 degrees C, and 30 degrees C, respectively; for group 2 -72 degrees C, -25 degrees C, 5 degrees C, 25 degrees C; and for Group 3 -82 degrees C, -30 degrees C, -12 degrees C, 13 degrees C. Complete necrosis was seen 5 mm from the cryoprobe within each group, but only in groups 2 and 3 did necrosis extend 10 mm or beyond the probes when utilizing either single or double probes. The maximum diameter of consistent necrosis was 35 to 40 mm in the animals in group 3 treated with a double probe. Bleeding and renal fracture were the two most common complications.

A 5-minute freeze appears to be inadequate to cause tissue necrosis and is associated with excessive bleeding at the time of the procedure, whereas the 15-minute freeze produces consistent necrosis but is associated with renal fracture. In this animal model, the 10-minute freeze with the single or double probe configuration appears optimal to produce necrosis without complications.