The rectal ‘no man's land’ and sphincter preservation during rectal excision

Abstract

Colorectal surgeons are familiar with the ‘holy plane’ as the key to total mesorectal excision (TME). Although this has revolutionized the surgical treatment of rectal cancer1, another term should now be introduced into the surgical lexicon – the rectal ‘no man’s land’. This is the area of the distal rectum that lies within the pelvic floor musculature. It cannot usually be reached from the abdomen and has been relatively inviolate as far as surgical exploration is concerned, although its anterior compartment has been accessed by the coloproctologist and gynaecologist during rectocele repair and by the urologist during perineal prostatectomy. This region varies in length depending on age, sex and body habitus. It is this variability that determines the length of retained diseased rectal cuff (ranging from a few millimetres to several centimetres) during restorative proctocolectomy for ulcerative colitis. Retention of long lengths may mar the functional result and increases the risk of carcinoma development, particularly in the presence of dysplasia2. To avoid such a potential disaster, coloproctologists either resort to mucosectomy and transanal anastomosis or panproctocolectomy. Both have drawbacks; mucosectomy may be incomplete, risks damage to the underlying internal sphincter and may cause incontinence, whereas after panproctocolectomy the patient is left with a permanent stoma3,4. Similarly, in low rectal cancer, if tumour clearance does not leave sufficient rectal stump to facilitate a stapled anastomosis, the sphincter-saving resection is invariably abandoned in favour of an abdominoperineal excision. It is interesting to note that even in the modern era of stapling up to 52 per cent of patients undergoing surgery for rectal cancer may still be left with a permanent stoma5. Although a minority of surgeons in such circumstances may attempt a partial sphincter-conserving procedure, notably the intersphincteric approach, concerns about technical difficulty, tumour clearance and functional outcome have limited its use6–8. If access could be obtained easily to the crucial few centimetres of distal rectum lying between the superior border of the levator ani which forms the pelvic floor within the abdomen and the anorectal junction in the perineum, it should be feasible to preserve the sphincteric apparatus virtually intact. By doing so it might be possible to increase the proportion of sphincter-saving resections without jeopardizing cure. Such an approach has been developed and should significantly reduce the need for a permanent stoma in patientswith benign and malignant rectal disease. So how can this ‘no man’s land’ be explored? For many years urologists used the anterior compartment of this space for the perineal approach to prostatectomy. As a result of elegant anatomical studies, Walsh9 demonstrated the feasibility of excising the prostate without damaging the nervi erigentes that enter the prostate at its inferolateral poles. To access the prostate, the dissection by necessity is in the rectoprostatic plane and begins above the external sphincter. Gynaecologists also pointed theway by using the rectovaginal plane in the course of posterior colporrhaphy, albeit by entering this space via the posterior vaginal wall. Both groups take great pains to avoid damage to the anterior wall of the rectum during dissection and of course have no desire to mobilize it. Dissection in the rectovaginal/ prostatic plane has been used in the development of an operation for rectal intussusception (the Express procedure)10. During development of this procedure it was realized that the rectum and mesorectum could be mobilized completely within the funnel of the pelvic floor musculature, and that the ‘no man’s land’ could be used for sphincter preservation. It was also demonstrated that the length of the rectum contained within this muscular funnel varied significantly. Although this variation was anatomical in that it was fixed according to body habitus, it was also obvious that some variation was operator dependent. Thus, in the course of an anterior resection for low rectal cancer, the extent of rectal mobilization down to the pelvic floor via the abdomen differs according to the surgeon’s skill and perseverance, compounded by anatomical variation and the shape of the pelvis. This in turn influences the length of rectum and mesorectum that remains for construction of the colorectal anastomosis. Exploitation of the rectal