Physiological study of anal sphincteric resection in an experimental porcine model

This study was conducted to compare and evaluate the extent of anal sphincteric resection and the degree of anal dysfunction in sphincter saving operations for lower rectal cancer using experimental porcine models. Each 10 Clawn miniature pigs underwent transanal intersphincteric resection (ISR), ISR with partial (one-quarter) external sphincteric resection (ESR-25%), and ISR with partial (one-half) external sphincteric resection (ESR-50%). An anorectal physiological study was performed before, one month, and three months after surgery in these three groups. The anal maximum resting pressure (AMRP) decreased from 45.1 cmH(2)O in the control group to 14.8, 14.3 and 11.1 cmH(2)O one month after surgery, and to 15.2, 8.8 and 5.2 cmH(2)O three months after surgery, in the ISR, ESR-25% and ESR-50% groups, respectively. The anal maximum squeezing pressure (AMSP) decreased from 81.7 cmH(2)O in the control group to 42.1, 40.1 and 41.1 cmH(2)O one month after surgery in the ISR, ESR-25% and ESR-50% groups, respectively. Three months after surgery, the MSP increased to 78.1 and 68.1 cmH(2)O in the ISR and ESR-25% groups, respectively, but the ESR-50% group showed a significantly lower MSP of 39.2 cmH(2)O compared with other two groups. The ratio of the potential difference on electromyographic (EMG) was 0.19 in the ESR-50% group, and this value was significantly lower than 0.8 in the ISR and ESR-25% groups, one month after surgery. Three months after surgery, the potential ratio of EMG was increased almost to the preoperative level both in the ISR and ESR-25% groups, but the ratio of the potential difference in the ESR-50% group with redness, sore and soiling around anus was 0.19 and significantly lower compared with other groups. The results of this study indicate that porcine models with additional resection of less than one quarter of the external anal sphincter have little anal dysfunction. A human clinical trial is needed to determine the ESR for very low rectal cancer.