Optimizing the selection of patients with low rectal cancer for intersphincteric resection by evaluating vertical invasion to the levator and external sphincter

AimThe indications for intersphincteric (ISR) anterior resection are not clearly defined. The aim of this study was to evaluate vertical extension of T2 or T3 low rectal cancer treated by rectal amputation to optimize patient selection for ISR. MethodThe abdominoperineal excision specimens of T2 or T3 low rectal cancer from 53 patients treated between 1992 and 2004 were retrospectively reviewed. Vertical invasion was quantified by measuring the shortest distance between the tumour and the striated muscle (T-SM), assuming that this represented the surgical margin that would have be achieved had an ISR been performed. ResultsInvolvement of the dentate line (DL) and intramural distal spread were independent risk factors for T-SM 2mm. The T-SM was less when the inferior border of the tumour was on the distal side of the DL (r=0.572, P<0.001). The probability of involvement of the DL, intramural distal spread or either one of these being associated with T-SM2mm was 43, 46 and 43%, respectively. All patients without both intramural distal spread and involvement of the DL had T-SM>2. ConclusionWe recommend that ISR should only be performed for patients with T2 or T3 low rectal cancer in whom the lowest edge of the tumour is above the DL and there is no intramural distal spread. Such patients are relatively unlikely to have a T-SM 2mm.