Partial in-vitro resistance to direct cryothermic injury in human leiomyomata and myometrium

Uterine leiomyomata are the most common pelvic tumor in women. Minimally invasive cryosurgery is being investigated as a therapeutic option for symptomatic women. Direct cryothermic cell injury thresholds for leiomyomata and the adjacent myometrium are not well quantified. Using a directional solidification stage to simulate in-vivo cryothermic cooling, tissue sections (3 mm) from ten leiomyomata and six portions of myometrium were cooled (5°C/min) to -20°C, -40°C, -60°C, and 80°C, held for 15 minutes, and then rapidly thawed to 21°C. In conjunction with tissue culturing and appropriate controls, cell death was assessed using a viability dye (ethidium homodimer/Hoechst) and routine histology. After normalizing to controls, leiomyomata cell death (LCD) increased from -20 to -80°C by histology (12 to 27 percent LCD) and dye assay (26 to 38 percent LCD). Myometrial cell death (MCD) from -20 to -80°C was 10 to 12 percent by histology and 4 to 20 percent by dye assay. In contrast to LCD from -40 to -80°C, MCD was significantly less and plateaued over this range (p<0.05). The dye assay appears to be more sensitive for detecting cell death than histology. This study suggests that both leiomyomata and myometrium are moderately resistant to direct cryothermic injury, with leiomyomata somewhat more susceptible.