External sphincter infiltration represents the only absolute indication of APR, whereas internal sphincter infiltration may be treated with an intersphinc-teric resection, giving good functional and oncological results .
The existence of an anatomic and functional division between the puborectalis muscle and external anal sphincter allows, in limited experiences, excision of the rectum and puborectalis, preserving the external sphincter . At the same distance from the rectum, a small sized tumour may be treated by conservative exeresis, whereas an APR is advisable to treat more extended cancer. This is not for reasons of local invasion, as there is no study showing a correlation between tumour volume and sphincter infiltration, but mainly for technical reasons of local and nervous dissection.
Preoperative radiotherapeutic overdosage may equally lead to avoidance of a colo-anal anastomosis.
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